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| features ? high performance, low power atmel ? avr ? 8-bit microcontroller ? advanced risc architecture ? 130 powerful instructions ? most single clock cycle execution ? 32 x 8 general purpose working registers ? fully static operation ? up to 16mips throughput at 16mhz ? on-chip 2-cycle multiplier ? high endurance non-volatile memory segments ? in-system self-programmable flash program memory ? 32kbytes (atmega325/atmega3250) ? 64kbytes (atmega645/atmega6450) ?eeprom ? 1kbytes (atmega325/atmega3250) ? 2kbytes (atmega645/atmega6450) ? internal sram ? 2kbytes (atmega325/atmega3250) ? 4kbytes (atmega645/atmega6450) ? write/erase cycles: 10,000 flash/ 100,000 eeprom ? data retention: 20 years at 85c/100 years at 25c (1) ? optional boot code secti on with independent lock bits ? in-system programming by on-chip boot program ? true read-while-write operation ? programming lock for software security ? atmel ? qtouch ? library support ? capacitive touch buttons, sliders and wheels ? qtouch and qmatrix ? acquisition ? up to 64 sense channels ? jtag (ieee std. 1149.1 compliant) interface ? boundary-scan capabilities according to the jtag standard ? extensive on-chip debug support ? programming of flash, eeprom, fuses, and lock bits through the jtag interface ? peripheral features ? two 8-bit timer/counters with separate prescaler and compare mode ? one 16-bit timer/counter with separate prescaler, compare mode, and capture mode ? real time counter with separate oscillator ? four pwm channels ? 8-channel, 10-bit adc ? programmable serial usart ? master/slave spi serial interface ? universal serial interface wi th start condition detector ? programmable watchdog timer with separate on-chip oscillator ? on-chip analog comparator ? interrupt and wake-up on pin change ? special microcontroller features ? power-on reset and programmable brown-out detection ? internal calibrated oscillator ? external and internal interrupt sources ? five sleep modes: idle, adc noise reduction, power-save, power-down, and standby ? i/o and packages ? 53/68 programmable i/o lines ? 64-lead tqfp, 64-pad qfn/mlf, and 100-lead tqfp ? speed grade: ? atmega325v/atmega3250v/a tmega645v/atmega6450v: ? 0 - 4mhz @ 1.8 - 5.5v; 0 - 8mhz @ 2.7 - 5.5v ? atmel atmega325/3250/645/6450: ? 0 - 8mhz @ 2.7 - 5.5v; 0 - 16mhz @ 4.5 - 5.5v ? temperature range: ?-40 c to 85 c industrsial ? ultra-low power consumption ? active mode: 1mhz, 1.8v: 350a 32khz, 1.8v: 20a (including oscillator) ? power-down mode: 100 na at 1.8v 8-bit atmel microcontroller with in-system programmable flash atmega325/v atmega3250/v atmega645/v atmega6450/v 2570n?avr?05/11
2 2570n?avr?05/11 atmega325/3250/645/6450 1. pin configurations figure 1-1. pinout atmega3250/6450 (oc2a/pci n t15) pb7 d n c (t1) pg3 (t0) pg4 reset/pg5 v cc g n d xtal2 (tosc2) xtal1 (tosc1) d n c d n c (pci n t26) pj2 (pci n t27) pj3 (pci n t28) pj4 (pci n t29) pj5 (pci n t30) pj6 d n c (icp1) pd0 (i n t0) pd1 pd2 pd3 pd4 pd5 pd6 pd7 a v cc ag n d aref pf0 (adc0) pf1(adc1) pf2 (adc2) pf3 (adc3) pf4 (adc4/tck) pf5 (adc5/tms) pf6 (adc6/tdo) pf7 (adc7/tdi) d n c d n c ph7 (pci n t23) ph6 (pci n t22) ph5 (pci n t21) ph4 (pci n t20) d n c d n c g n d v cc d n c pa 0 pa 1 pa 2 d n c (rxd/pci n t0) pe0 (txd/pci n t1) pe1 (xck/ai n 0/pci n t2) pe2 (ai n 1/pci n t3) pe3 (usck/scl/pci n t4) pe4 (di/sda/pci n t5) pe5 (do/pci n t6) pe6 (clko/pci n t7) pe7 v cc g n d d n c (pci n t24) pj0 (pci n t25) pj1 d n c d n c d n c d n c (ss/pci n t8) pb0 (sck/pci n t9) pb1 (mosi/pci n t10) pb2 (miso/pci n t11) pb3 (oc0a/pci n t12) pb4 (oc1a/pci n t13) pb5 (oc1b/pci n t14) pb6 pa 3 pa 4 pa 5 pa 6 pa 7 pg2 pc7 pc6 d n c ph3 (pci n t19) ph2 (pci n t18) ph1 (pci n t17) ph0 (pci n t16) d n c d n c d n c d n c pc5 pc4 pc3 pc2 pc1 pc0 pg1 pg0 i n dex cor n er atme g a 3 250/6450 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 75 74 73 72 71 70 69 68 67 66 65 64 63 62 61 60 59 58 57 56 55 54 53 52 51 100 99 98 97 96 95 94 93 92 91 90 89 88 87 86 85 84 83 82 81 80 79 78 77 76 3 2570n?avr?05/11 atmega325/3250/645/6450 figure 1-2. pinout atmega325/645 note: the large center pad underneath the qfn/ml f packages is made of metal and internally con- nected to gnd. it should be soldered or glued to the board to ensure good mechanical stability. if the center pad is left unc onnected, the package might loosen from the board. pc0 v cc g n d pf0 (adc0) pf7 (adc7/tdi) pf1 (adc1) pf2 (adc2) pf3 (adc3) pf4 (adc4/tck) pf5 (adc5/tms) pf6 (adc6/tdo) aref g n d a v cc 17 61 60 18 59 20 58 19 21 57 22 56 23 55 24 54 25 53 26 52 27 51 29 28 50 49 32 31 30 (rxd/pci n t0) pe0 (txd/pci n t1) pe1 (xck/ai n 0/pci n t2) pe2 (ai n 1/pci n t3) pe3 (usck/scl/pci n t4) pe4 (di/sda/pci n t5) pe5 (do/pci n t6) pe6 (clko/pci n t7) pe7 (sck/pci n t9) pb1 (mosi/pci n t10) pb2 (miso/pci n t11) pb3 (oc0a/pci n t12) pb4 (oc2a/pci n t15) pb7 (t1) pg3 (oc1b/pci n t14) pb6 (t0) pg4 (oc1a/pci n t13) pb5 pc1 pg0 pd7 pc2 pc3 pc4 pc5 pc6 pc7 pa7 pg2 pa6 pa5 pa4 pa3 pa0 pa1 pa2 pg1 pd6 pd5 pd4 pd3 pd2 pd1 (i n t0) (icp1) pd0 xtal1 (tosc1) xtal2 (tosc2) reset/pg5 g n d v cc i n dex cor n er (ss/pci n t8) pb0 2 3 1 4 5 6 7 8 9 10 11 12 13 14 16 15 64 63 62 47 46 48 45 44 43 42 41 40 39 38 37 36 35 33 34 atme g a 3 25/645 d n c 4 2570n?avr?05/11 atmega325/3250/645/6450 2. overview the atmel atmega325/3250/645/6450 is a low-power cmos 8 -bit microcontroller based on the avr enhanced risc architecture. by executing pow erful instructions in a single clock cycle, the atmel atmega325/3250/645/6450 achieves throughputs approaching 1 mips per mhz allowing the system designer to optimize power consumption versus processing speed. 2.1 block diagram figure 2-1. block diagram the atmel ? avr ? core combines a rich instruction set with 32 general purpose working registers. all the 32 registers are directly connected to the arithmetic logic unit (alu), allowing two inde- pendent registers to be accessed in one single in struction executed in one clock cycle. the program counter internal oscillator watchdog timer stack pointer program flash mcu control register sram general purpose registers instruction register timer/ counters instruction decoder data dir. reg. portb data dir. reg. porte data dir. reg. porta data dir. reg. portd data register portb data register porte data register porta data register portd timing and control oscillator interrupt unit eeprom spi usart status register z y x alu portb drivers porte drivers porta drivers portf drivers portd drivers portc drivers pb0 - pb7 pe0 - pe7 pa0 - pa7 pf0 - pf7 vcc gnd xtal1 xtal2 control lines + - analog comp arator pc0 - pc7 8-bit data bus reset calib. osc data dir. reg. portc data register portc on-chip debug jtag tap programming logic boundary- scan data dir. reg. portf data register portf adc pd0 - pd7 data dir. reg. portg data reg. portg portg drivers pg0 - pg4 agnd aref avcc universal serial interface avr cpu porth drivers ph0 - ph7 data dir. reg. porth data register porth portj drivers pj0 - pj6 data dir. reg. portj data register portj 5 2570n?avr?05/11 atmega325/3250/645/6450 resulting architecture is more code efficient wh ile achieving throughputs up to ten times faster than conventional cisc microcontrollers. the atmel atmega325/3250/645/6450 provides the following features: 32/64k bytes of in-sys- tem programmable flash with read-while-write capabilities, 1/2k bytes eeprom, 2/4k byte sram, 54/69 general purpose i/o lines, 32 general purpose working registers, a jtag interface for boundary-scan, on-chip debugging support and programming, three flexible timer/counters with compare modes, internal and external interrupts, a serial programmable usart, universal serial interface with start condition detector, an 8 -channel, 10-bit adc, a programmable watchdog timer with internal osc illator, an spi serial port, and five software se lectable power saving modes. the idle mode stops the cpu while allowing the sram, timer/counters, spi port, and interrupt system to continue functioning. the power-down mode saves the register contents but freezes the oscillator, disabling all other chip functions until the next interrupt or hardware reset. in power-save mode, the asynchronous timer will continue to run, allowing the user to maintain a timer base while the rest of the device is sleeping. the adc noise reduction mode stops the cpu and all i/o modules except asynchronous timer and adc to minimize switching noise during adc conversions. in standby mode, the crystal/resonator oscillator is running while the rest of the device is sleeping. this allows very fast st art-up combined with low- power consumption. atmel offers the qtouch ? library for embedding capacitive touch buttons, sliders and wheels- functionality into avr microcontrollers. the patented charge-transfer signal acquisition offersrobust sensing and includes fully debounced reporting of touch keys and includes adjacent keysuppression ? (aks ? ) technology for unambiguous detection of key events. the easy-to-use qtouch suite toolchain allows you to explore, develop and debug your own touch applications. the device is manufactured using atmel?s high density non-volatile memory technology. the on-chip in-system re-programmable (isp) flash allows the program memory to be repro- grammed in-system through an spi serial interf ace, by a conventional non-volatile memory programmer, or by an on-chip boot program running on the avr core. the boot program can use any interface to download the application progr am in the application flash memory. soft- ware in the boot flash section will continue to run while the application flas h section is updated, providing true read-while-write operation. by combining an 8 -bit risc cpu with in-system self-programmable flash on a monolithic chip, the atmel atmel atmega325/3250/645/6450 is a powerful microcontroller that provides a highly flexible and cost effective solution to many embedded control applications. the atmel atmega325/3250/645/6450 is supported with a full suite of program and system development tools including: c compilers, macro assemblers, program debugger/simulators, in-circuit emulators, and evaluation kits. 6 2570n?avr?05/11 atmega325/3250/645/6450 2.2 comparison between atmega325, atmega3250, atmega645 and atmega6450 the atmega325, atmega3250, atmega645, and atmega6450 differ only in memory sizes, pin count and pinout. table 2-1 on page 6 summarizes the different configurations for the four devices. 2.3 pin descriptions the following section describes the i/o-pin special functions. 2.3.1 v cc digital supply voltage. 2.3.2 gnd ground. 2.3.3 port a (pa7..pa0) port a is an 8 -bit bi-directional i/o port with internal pull-up resistors (selected for each bit). the port a output buffers have symmetrical drive characteristics with both high sink and source capability. as inputs, port a pi ns that are externally pulled low will source current if the pull-up resistors are activated. the port a pins are tri-stated when a reset condition becomes active, even if the clock is not running. 2.3.4 port b (pb7..pb0) port b is an 8 -bit bi-directional i/o port with internal pull-up resistors (selected for each bit). the port b output buffers have symmetrical drive characteristics with both high sink and source capability. as inputs, port b pi ns that are externally pulled low will source current if the pull-up resistors are activated. the port b pins are tri-stated when a reset condition becomes active, even if the clock is not running. port b has better driving capabilities than the other ports. port b also serves the functions of various special features of the atmel atmega325/3250/645/6450 as listed on page 6 8 . 2.3.5 port c (pc7..pc0) port c is an 8 -bit bi-directional i/o port with internal pull-up resistors (selected for each bit). the port c output buffers have symmetrical drive c haracteristics with bot h high sink and source capability. as inputs, port c pi ns that are externally pulled lo w will source current if the pull-up resistors are activated. the port c pins are tri-stated when a reset condition becomes active, even if the clock is not running. table 2-1. configuration summary device flash eeprom ram general purpose i/o pins atmega325 32kbytes 1kbytes 2kbytes 54 atmega3250 32kbytes 1kbytes 2kbytes 69 atmega645 64kbytes 2kbytes 4kbytes 54 atmega6450 64kbytes 2kbytes 4kbytes 69 7 2570n?avr?05/11 atmega325/3250/645/6450 2.3.6 port d (pd7..pd0) port d is an 8 -bit bi-directional i/o port with internal pull-up resistors (selected for each bit). the port d output buffers have symmetrical drive c haracteristics with bot h high sink and source capability. as inputs, port d pi ns that are externally pulled lo w will source current if the pull-up resistors are activated. the port d pins are tri-stated when a reset condition becomes active, even if the clock is not running. port d also serves the functions of various special features of the atmel atmega325/3250/645/6450 as listed on page 71 . 2.3.7 port e (pe7..pe0) port e is an 8 -bit bi-directional i/o port with internal pull-up resistors (selected for each bit). the port e output buffers have symmetrical drive characteristics with both high sink and source capability. as inputs, port e pi ns that are externally pulled low will source current if the pull-up resistors are activated. the port e pins are tri-stated when a reset condition becomes active, even if the clock is not running. port e also serves the functions of various special features of the atmel atmega325/3250/645/6450 as listed on page 72 . 2.3.8 port f (pf7..pf0) port f serves as the analog inputs to the a/d converter. port f also serves as an 8 -bit bi-directional i/o port, if the a/d converter is not used. port pins can provide internal pull-up resistors (selected for each bit). the port f output buffers have sym- metrical drive characteristics with both high sink and source capa bility. as inputs, port f pins that are externally pulled low will source current if the pull-up resistors are ac tivated. the port f pins are tri-stated when a reset condition becomes active, even if the clock is not running. if the jtag interface is enabled, the pull-up resistors on pins pf7( tdi), pf5(tms), and pf4(tck) will be activated even if a reset occurs. port f also serves the functions of the jtag interface. 2.3.9 port g (pg5..pg0) port g is a 6-bit bi-directional i/o port with internal pull-up resistors (selected for each bit). the port g output buffers have symmetrical drive characteristics with both high sink and source capability. as inputs, port g pins that are extern ally pulled low will sour ce current if the pull-up resistors are activated. the port g pins are tri-stated when a reset condition becomes active, even if the clock is not running. port g also serves the functions of various special features of the atmel atmega325/3250/645/6450 as listed on page 72 . 2.3.10 port h (ph7..ph0) port h is a 8 -bit bi-directional i/o port with internal pull-up resistors (selected for each bit). the port h output buffers have symmetrical drive c haracteristics with bot h high sink and source capability. as inputs, port h pi ns that are externally pulled lo w will source current if the pull-up resistors are activated. the port h pins are tri-stated when a reset condition becomes active, even if the clock is not running. port h also serves the functions of various special features of the atmega3250/6450 as listed on page 72 . 8 2570n?avr?05/11 atmega325/3250/645/6450 2.3.11 port j (pj6..pj0) port j is a 7-bit bi-directional i/o port with internal pull-up resistors (selected for each bit). the port j output buffers have symmetrical drive characteristics with both high sink and source capa- bility. as inputs, port j pins that are externally pulled low will source current if the pull-up resistors are activated. the port j pins are tr i-stated when a reset condition becomes active, even if the clock is not running. port j also serves the functions of various special features of the atmega3250/6450 as listed on page 72 . 2.3.12 reset reset input. a low level on this pin for longer than the minimum pulse length will generate a reset, even if the clock is not running. the minimum pulse length is given in table 2 8 -4 on page 301 . shorter pulses are not guaranteed to generate a reset. 2.3.13 xtal1 input to the inverting oscillato r amplifier and input to the in ternal clock operating circuit. 2.3.14 xtal2 output from the invert ing oscillator amplifier. 2.3.15 avcc avcc is the supply voltage pin for port f and the a/d converter. it should be externally con- nected to v cc , even if the adc is not used. if the adc is used, it should be connected to v cc through a low-pass filter. 2.3.16 aref this is the analog reference pin for the a/d converter. 9 2570n?avr?05/11 atmega325/3250/645/6450 3. resources a comprehensive set of development tools, app lication notes and datasheets are available for download on http:// www.atmel.com/avr. note: 1. 4. data retention reliability qualification results show that the pr ojected data retention failure rate is much less than 1 ppm over 20 years at 8 5c or 100 years at 25c. 5. about code examples this documentation contains simple code examples that briefly show how to use various parts of the device. these code examples assume that the part specific header file is included before compilation. be aware that not all c compiler vendors include bit definitions in the header files and interrupt handling in c is compiler dependent. please confirm with the c compiler documen- tation for more details. for i/o registers located in extended i/o map, ?in?, ?out?, ?sbis?, ?sbic?, ?cbi?, and ?sbi? instructions must be replaced with instructio ns that allow access to extended i/o. typically ?lds? and ?sts? combined with ? sbrs?, ?sbrc?, ?sbr?, and ?cbr?. 6. capacitive touch sensing the atmel ? qtouch ? library provides a simple to use so lution to realize touch sensitive inter- faces on most atmel avr ? microcontrollers. the qtouch library includes support for the qtouch and qmatrix ? acquisition methods. touch sensing can be added to any application by linking the appropriate atmel qtouch library for the avr microcontroller. this is done by using a simple set of apis to define the touch chan- nels and sensors, and then calling the touch sens ing api?s to retrieve the channel information and determine the touch sensor states. the qtouch library is free and downloadable from the atmel website at the following location: www.atmel.com/qtouchlibrary . for implementation details and other information, refer to the atmel qtouch library user guide - also available for download from the atmel website. 10 2570n?avr?05/11 atmega325/3250/645/6450 7. avr cpu core 7.1 overview this section discusses the atmel ? avr ? core architecture in general. the main function of the cpu core is to ensure correct program execution. the cpu must therefore be able to access memories, perform calculations, control peripherals, and handle interrupts. 7.2 architectural overview figure 7-1. block diagram of the avr architecture in order to maximize performance and parallelism, the avr uses a harvard architecture ? with separate memories and buses for program and data. instructions in the program memory are executed with a single level pipelining. while one instruction is being executed, the next instruc- tion is pre-fetched from the program memory. this concept enables instructions to be executed in every clock cycle. the program memory is in-system reprogrammable flash memory. flash program memory instruction register instruction decoder program counter control lines 32 x 8 general purpose registrers alu status and control i/o lines eeprom data bus 8 -bit data sram direct addressing indirect addressing interrupt unit spi unit watchdog timer analog comparator i/o module 2 i/o module1 i/o module n 11 2570n?avr?05/11 atmega325/3250/645/6450 the fast-access register file contains 32 x 8 -bit general purpose working registers with a single clock cycle access time. this allows single-cycle ar ithmetic logic unit (alu ) operation. in a typ- ical alu operation, two operands are output from the register file, the operation is executed, and the result is stored back in the register file ? in one clock cycle. six of the 32 registers can be used as three 16-b it indirect address register pointers for data space addressing ? enabling efficient address calculations. one of the these address pointers can also be used as an address pointer for look up tables in flash program memory. these added function registers are the 16-bit x-, y-, and z-register, described later in this section. the alu supports arithmetic and logic operations between registers or between a constant and a register. single register operations can also be executed in the alu. after an arithmetic opera- tion, the status register is updated to reflect information about the result of the operation. program flow is provided by conditional and uncon ditional jump and call instructions, able to directly address the whole address space. most avr instructions have a single 16-bit word for- mat. every program memory address contains a 16- or 32-bit instruction. program flash memory space is divided in two sections, the boot program section and the application program section. both sections have dedicated lock bits for write and read/write protection. the spm instruction that writes into the application flash memory section must reside in the boot program section. during interrupts and subroutine calls, the return address program counter (pc) is stored on the stack. the stack is effectively allocated in the general data sram, and consequently the stack size is only limited by the to tal sram size and the usage of the sram. all user programs must initialize the sp in the reset routine (before subroutines or interrupts are executed). the stack pointer (sp) is read/write accessible in the i/o space. the data sram can easily be accessed through the five different addressing modes supported in the avr architecture. the memory spaces in the avr architecture are all linear and regular memory maps. a flexible interrupt module has its control r egisters in the i/o space with an additional global interrupt enable bit in the status register. all interrupts have a separate interrupt vector in the interrupt vector table. the interrupts have priority in accordance with their interrupt vector posi- tion. the lower the interrupt vector address, the higher the priority. the i/o memory space contains 64 addresses for cpu peripheral functi ons as control regis- ters, spi, and other i/o functions. the i/o memory can be accessed directly, or as the data space locations following those of the register file, 0x20 - 0x5f. in addition, the atmel atmega325/3250/645/6450 has extended i/o space from 0x60 - 0xff in sram where only the st/sts/std and ld/lds/ldd instructions can be used. 7.3 alu ? arithm etic logic unit the high-performance avr alu operates in dire ct connection with all the 32 general purpose working registers. within a single clock cycle, arithmetic operations between general purpose registers or between a register and an immediate are executed. the alu operations are divided into three main categories ? arithmetic, logical, and bit-functions. some implementations of the architecture also provide a powerful multiplier supporting both signed/unsigned multiplication and fractional format. see the ?instruction set? section for a detailed description. 12 2570n?avr?05/11 atmega325/3250/645/6450 7.4 status register the status register contains information about the result of the most recently executed arithme- tic instruction. this information can be used for altering program flow in order to perform conditional operations. note that the status register is updated after all alu operations, as specified in the instruction set reference. this will in many cases remove the need for using the dedicated compare instructions, resulting in faster and more compact code. the status register is not automatically stored when entering an interrupt routine and restored when returning from an interrupt. this must be handled by software. 7.4.1 sreg ? avr status register the avr status register ? sreg ? is defined as: ? bit 7 ? i: global interrupt enable the global interrupt enable bit must be set for th e interrupts to be enabled. the individual inter- rupt enable control is then performed in separate control registers. if the global interrupt enable register is cleared, none of the interrupts are enabled independent of the individual interrupt enable settings. the i-bit is cleared by hardware after an interrupt has occurred, and is set by the reti instruction to enable subsequent interrupts. the i-bit can also be set and cleared by the application with the sei and cli instructions, as described in the instruction set reference. ? bit 6 ? t: bit copy storage the bit copy instructions bld (bit load) and bst (b it store) use the t-bit as source or desti- nation for the operated bit. a bit from a register in the register file can be copied into t by the bst instruction, and a bit in t can be copied into a bit in a register in the register file by the bld instruction. ? bit 5 ? h: half carry flag the half carry flag h indicates a half carry in so me arithmetic operations. half carry is useful in bcd arithmetic. see the ?instruction set description? for detailed information. ? bit 4 ? s: sign bit, s = n v the s-bit is always an exclusive or between the negative flag n and the two?s complement overflow flag v. see the ?instruction set description? for detailed information. ? bit 3 ? v: two?s complement overflow flag the two?s complement overflow flag v suppor ts two?s complement arithmetics. see the ?instruction set description? for detailed information. ? bit 2 ? n: negative flag the negative flag n indicates a negative result in an arithmetic or logic operation. see the ?instruction set description? for detailed information. ? bit 1 ? z: zero flag the zero flag z indicates a zero result in an arithmetic or logic operation. see the ?instruction set description? for detailed information. bit 76543210 0x3f (0x5f) i t h s v n z c sreg read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 13 2570n?avr?05/11 atmega325/3250/645/6450 ? bit 0 ? c: carry flag the carry flag c indicates a carry in an arithmetic or logic operation. see the ?instruction set description? for de tailed information. 7.5 general purpose register file the register file is optimized for the avr enhanc ed risc instruction set. in order to achieve the required performance and flex ibility, the following in put/output schemes ar e supported by the register file: ?one 8 -bit output operand and one 8 -bit result input ?two 8 -bit output operands and one 8 -bit result input ?two 8 -bit output operands and one 16-bit result input ? one 16-bit output operand and one 16-bit result input figure 7-2 on page 13 shows the structure of the 32 general purpose working registers in the cpu. figure 7-2. avr cpu general purpose working registers most of the instructions operating on the register file have direct access to all registers, and most of them are single cycle instructions. as shown in figure 7-2 on page 13 , each register is also assigned a data memory address, mapping them directly into the first 32 location s of the user data space. although not being physically implemented as sram locations, this memory organiza tion provides great flexibility in access of the registers, as the x-, y- and z-pointer registers can be set to index any register in the file. 7.5.1 the x-register, y-register, and z-register the registers r26..r31 have some added functions to their general purpose usage. these reg- isters are 16-bit address pointers for indirect addressing of the data space. the three indirect address registers x, y, and z are defined as described in figure 7-3 on page 14 . 7 0 addr. r0 0x00 r1 0x01 r2 0x02 ? r13 0x0d general r14 0x0e purpose r15 0x0f working r16 0x10 registers r17 0x11 ? r26 0x1a x-register low byte r27 0x1b x-register high byte r2 8 0x1c y-register low byte r29 0x1d y-register high byte r30 0x1e z-register low byte r31 0x1f z-register high byte 14 2570n?avr?05/11 atmega325/3250/645/6450 figure 7-3. the x-, y-, and z-registers in the different addressing modes these address registers have functions as fixed displacement, automatic increment, and automatic decrement (see the instruction set reference for details). 7.6 stack pointer the stack is mainly used for storing temporary data, for storing local variables and for storing return addresses after interrupts and subroutine calls. the stack pointer register always points to the top of the stack. note that the stack is implemented as growing from higher memory loca- tions to lower memory locations. this implies that a stack push command decreases the stack pointer. the stack pointer points to the data sram stack area where the subroutine and interrupt stacks are located. this stack space in the data sram must be defined by the program before any subroutine calls are executed or interrupts are enabled. the stack pointer must be set to point above 0x60. the stack pointer is decrement ed by one when data is pushed onto the stack with the push instruction, and it is decremented by two when the return address is pushed onto the stack with subroutine call or interrupt. the stack pointer is incremented by one when data is popped from the stack with the pop instruction, and it is incremented by two when data is popped from the stack with return from subroutine ret or return from interrupt reti. the avr stack pointer is implemented as two 8 -bit registers in the i/o space. the number of bits actually used is implementation dependent. note that the data space in some implementa- tions of the avr architecture is so small that only spl is needed. in this case, the sph register will not be present. 7.7 instruction execution timing this section describes the general access timi ng concepts for instruction execution. the avr cpu is driven by the cpu clock clk cpu , directly generated from the selected clock source for the chip. no internal clo ck division is used. figure 7-4 on page 15 shows the parallel instruction fetches and instruction executions enabled by the harvard architecture and the fast-access r egister file concept. this is the basic pipelin- 15 xh xl 0 x-register 707 0 r27 (0x1b) r26 (0x1a) 15 yh yl 0 y-register 707 0 r29 (0x1d) r2 8 (0x1c) 15 zh zl 0 z-register 70 7 0 r31 (0x1f) r30 (0x1e) bit 151413121110 9 8 0x3e (0x5e) sp15 sp14 sp13 sp12 sp11 sp10 sp9 sp8 sph 0x3d (0x5d) sp7 sp6 sp5 sp4 sp3 sp2 sp1 sp0 spl 76543210 read/write r/w r/w r/w r/w r/w r/w r/w r/w r/w r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 00000000 15 2570n?avr?05/11 atmega325/3250/645/6450 ing concept to obtain up to 1 mips per mhz with the corresponding unique results for functions per cost, functions per clocks, and functions per power-unit. figure 7-4. the parallel instruction fetches and instruction executions figure 7-5 on page 15 shows the internal timing concept for the register file. in a single clock cycle an alu operation using two register operands is executed, and the result is stored back to the destination register. figure 7-5. single cycle alu operation 7.8 reset and inte rrupt handling the avr provides several different interrupt sources. these interrupts and the separate reset vector each have a separate program vector in the program memory space. all interrupts are assigned individual enable bits which must be written logic one together with the global interrupt enable bit in the status register in orde r to enable the interrupt. depending on the program counter value, interrupts may be automatically disabled when boot lock bits blb02 or blb12 are programmed. this feature improves software security. see the section ?memory program- ming? on page 265 for details. the lowest addresses in the program memory space are by default defined as the reset and interrupt vectors. the complete list of vectors is shown in ?interrupts? on page 49 . the list also determines the priority levels of the different interrupts. the lower the address the higher is the priority level. reset has the highest priority, and next is int0 ? the external interrupt request 0. the interrupt vectors can be moved to the start of the boot flash section by setting the ivsel bit in the mcu control r egister (mcucr). refer to ?interrupts? on page 49 for more information. the reset vector can also be moved to the start of the boot flash section by programming the bootrst fuse, see ?boot loader support ? read-while-write self-programming? on page 251 . clk 1st instruction fetch 1st instruction execute 2nd instruction fetch 2nd instruction execute 3rd instruction fetch 3rd instruction execute 4th instruction fetch t1 t2 t3 t4 cpu total execution time register operands fetch alu operation execute result write back t1 t2 t3 t4 clk cpu 16 2570n?avr?05/11 atmega325/3250/645/6450 when an interrupt occurs, the global interrupt enable i-bit is cleared and all interrupts are dis- abled. the user software can write logic one to the i-bit to enable nested interrupts. all enabled interrupts can then interrupt the current interrupt routine. the i-bit is automatically set when a return from interrupt instruction ? reti ? is executed. there are basically two types of interrupts. the fi rst type is triggered by an event that sets the interrupt flag. for these interrupts, the program counter is vectored to the actual interrupt vec- tor in order to execute the interrupt handling routine, and hardware clears the corresponding interrupt flag. interrupt flags can also be cleared by writing a logic one to the flag bit position(s) to be cleared. if an interrupt condition occurs while the corresponding interrupt enable bit is cleared, the interrupt fl ag will be set and remember ed until the interrupt is enabled, or the flag is cleared by software. similarly, if one or more interrupt conditions occur while the global interrupt enable bit is clea red, the corres ponding interrupt fl ag(s) will be set and remembered until the global interrupt enable bit is set, and will then be exec uted by order of priority. the second type of interrupts will trigger as long as the interrupt condition is present. these interrupts do not necessarily have interrupt flags. if the interrupt condition disappears before the interrupt is enabled, the in terrupt will not be triggered. when the avr exits from an inte rrupt, it will always retu rn to the main pr ogram and execute one more instruction before any pending interrupt is served. note that the status register is not automatica lly stored when entering an interrupt routine, nor restored when returning from an interrupt routine. this must be handled by software. when using the cli instruction to disable interrupts, the interrup ts will be immediately disabled. no interrupt will be executed af ter the cli instruction, even if it occurs simultaneously with the cli instruction. the following example shows how this can be used to avoid interrupts during the timed eeprom write sequence. assembly code example in r16, sreg ; store sreg value cli ; disable interrupts during timed sequence sbi eecr, eemwe ; start eeprom write sbi eecr, eewe out sreg, r16 ; restore sreg value (i-bit) c code example char csreg; csreg = sreg; /* store sreg value */ /* disable interrupts during timed sequence */ __disable_interrupt(); eecr |= (1< 18 2570n?avr?05/11 atmega325/3250/645/6450 8. avr memories this section describes the different memories in the atmel atmega325/3250/645/6450. the avr architecture has two main memory spaces, the data memory and the program memory space. in addition, the at mel atmega325/32 50/645/6450 features an eeprom memory for data storage. all three memory spaces are linear. 8.1 in-system reprogrammable flash program memory the atmel atmega325/3250/645/6450 contains 32/64k bytes on-chip in-system reprogram- mable flash memory for program storage. since all avr instructions are 16 or 32 bits wide, the flash is organized as 16/32k x 16. for software security, the flash program memory space is divided into two sections, boot program section and application program section. the flash memory has an endurance of at l east 10,000 write/erase cycles. the atmel atmega325/3250/645/6450 program counter (pc) is 14/15 bits wide, thus addressing the 16/32k program memory locations. the operation of boot program section and associated boot lock bits for software protection are described in detail in ?boot loader support ? read-while- write self-programming? on page 251 . ?memory programming? on page 265 contains a detailed description on flash data serial downloading using the spi pins or the jtag interface. constant tables can be allocated within the entire program memory address space (see the lpm ? load program memory instruction description). timing diagrams for instruction fetch and execution are presented in ?instruction execution tim- ing? on page 14 . figure 8-1. program memory map 0x0000 0x3fff/0x7fff program memory application flash section boot flash section 19 2570n?avr?05/11 atmega325/3250/645/6450 8.2 sram data memory figure 8 -2 on page 19 shows how the atmel atmega325/3250/645/6450 sram memory is organized. the atmel atmega325/3250/645/6450 is a complex microcontroller with more peripheral units than can be supported within the 64 locations reserved in the opcode for the in and out instructions. for the extended i/o space from 0x60 - 0xff in sram, only the st/sts/std and ld/lds/ldd instructions can be used. the lower 2304/4352 data memory locations address both the register file, the i/o memory, extended i/o memory, and the internal data sr am. the first 32 locations address the register file, the next 64 location the standard i/o memory, then 160 locations of extended i/o memory, and the next 204 8 /4096 locations address the internal data sram. the five different addressing modes for the data memory cover: direct, indirect with displace- ment, indirect, indirect with pre-decrement, and indirect with post-increment. in the register file, registers r26 to r31 feature the indirect addressing pointer registers. the direct addressing reaches the entire data space. the indirect with displacement mode reaches 63 address locations from the base address given by the y- or z-register. when using register indirect addressing modes with automatic pre-decrement and post-incre- ment, the address registers x, y, and z are decremented or incremented. the 32 general purpose working registers, 64 i /o registers, 160 extended i/o registers, and the 2,04 8 bytes of internal data sram in the atmel atmega325/3250/645/6450 are all accessi- ble through all these addressing modes. the register file is described in ?general purpose register file? on page 13 . figure 8-2. data memory map 8.2.1 data memory access times this section describes the general access timi ng concepts for internal memory access. the internal data sram access is performed in two clk cpu cycles as described in figure 8 -3 . 32 registers 64 i/o registers internal sram (2048 x 8)/ (4096 x 8) 0x0000 - 0x001f 0x0020 - 0x005f 0x08ff/0x10ff 0x0060 - 0x00f f data memory 160 ext i/o reg. 0x0100 20 2570n?avr?05/11 atmega325/3250/645/6450 figure 8-3. on-chip data sram access cycles 8.3 eeprom data memory the atmel atmega325/3250/645/6450 contains 1/2k bytes of data eeprom memory. it is organized as a separate data space, in which single bytes can be read and written. the eeprom has an endurance of at least 100,000 write/erase cycles. the access between the eeprom and the cpu is described in the follow ing, specifying the eeprom address regis- ters, the eeprom data register, and the eeprom control register. for a detailed description of spi, jtag and parallel data downloading to the eeprom, see page 2 8 0 , page 2 8 4 , and page 26 8 respectively. 8.3.1 eeprom read/write access the eeprom access registers are accessible in the i/o space. the write access time for the eeprom is given in table 8 -1 . a self-timing function, however, lets the user software detect when the next byte can be written. if the user code contains instruc- tions that write the eeprom, some precautions must be taken. in heavily filtered power supplies, v cc is likely to rise or fall slowly on po wer-up/down. this causes the device for some period of time to run at a voltage lower than specified as minimum for the clock frequency used. see ?preventing eeprom co rruption? on page 21. for details on how to avoid problems in these situations. in order to prevent unintentional eeprom writes, a specific write procedure must be followed. refer to the description of the eeprom control regist er for details on this. when the eeprom is read, the cpu is halted for fo ur clock cycles before the next in struction is executed. when the eeprom is written, the cp u is halted for two clock cycles before the next instruction is executed. 8.3.2 eeprom write during power-down sleep mode when entering power-down sleep mode whil e an eeprom write operation is active, the eeprom write operation will continue, and will complete before the write access time has passed. however, when the write operation is completed, the clock continues running, and as a clk wr rd data data address address valid t1 t2 t3 compute address read write cpu memory access instruction next instruction 21 2570n?avr?05/11 atmega325/3250/645/6450 consequence, the device does not enter power-down entirely. it is therefore recommended to verify that the eeprom write operation is completed before entering power-down. 8.3.3 preventing eeprom corruption during periods of low v cc, the eeprom data can be corrupted because the supply voltage is too low for the cpu and the eeprom to operate properly. these issues are the same as for board level systems using eepr om, and the same design so lutions should be applied. an eeprom data corruption can be caused by two situations when the voltage is too low. first, a regular write sequence to the eeprom requires a minimum voltage to operate correctly. sec- ondly, the cpu itself can execute instructions incorrectly, if the supp ly voltage is too low. eeprom data corruption can ea sily be avoided by followin g this design recommendation: keep the avr reset active (low) during periods of insufficient power su pply voltage. this can be done by enabling the internal brown-out detector (bod). if the detection level of the internal bod does not match the needed detection level, an external low v cc reset protection circuit can be used. if a reset occurs while a write operation is in progress , the write operation will be com- pleted provided that the power supply voltage is sufficient. 8.4 i/o memory the i/o space definition of the atmel atmega325/3250/645/6450 is shown in ?register sum- mary? on page 336 . all atmel atmega325/3250/645/6450 i/os and peripherals are placed in the i/o space. all i/o locations may be accessed by the ld/lds/ldd and st/sts/std instructions, transferring data between the 32 general purpose working registers and the i/o space. i/o registers within the address range 0x00 - 0x1f are directly bit-acce ssible using the sbi an d cbi instructions. in these registers, the value of single bits can be checked by using the sbis and sbic instructions. refer to the instruction set section for more details. when using the i/o specific commands in and out, the i/o addresses 0x00 - 0x3f must be used. when addressing i/o registers as data space using ld and st instructions, 0x20 must be added to these addresses. the atmel atmega325/3250/645/6450 is a complex microcontroller with more peripheral units than can be supported within the 64 location reserved in opcode for the in and out instructions. for the extended i/o space from 0x60 - 0xff in sram, only the st/sts/std and ld/lds/ldd instruc- tions can be used. for compatibility with future devices, reserved bits should be written to zero if accessed. reserved i/o memory addresses should never be written. some of the status flags are cleared by writing a logical one to them. note that, unlike most other avrs, the cbi and sbi instructions will only operate on the specified bit, and can therefore be used on registers containing such status flags. the cbi and sbi instructions work with reg- isters 0x00 to 0x1f only. the i/o and peripherals control registers are explained in later sections. 8.4.1 general purpose i/o registers the atmel atmega325/3250/645/6450 contains three general purpose i/o registers. these registers can be used for storing any information, and they are particularly useful for storing global variables and status flags. general pu rpose i/o registers within the address range 0x00 - 0x1f are directly bit-accessible using the sbi, cbi, sbis, and sbic instructions. 22 2570n?avr?05/11 atmega325/3250/645/6450 8.5 register description 8.5.1 eearh and eearl ? the eeprom address register ? bits 15:11 ? reserved bits these bits are reserved bits in the atmel atmega325/3250/645/6450 and will always read as zero. ? bits 10:0 ? eear10:0: eeprom address the eeprom address registers ? eearh and eearl specify the eeprom address in the 1/2k bytes eeprom space. the eeprom data bytes are addressed linearly between 0 and 1023/2047. the initial value of eear is undefined. a proper valu e must be written before the eeprom may be accessed. note: eear10 is only valid for atmega645 and atmega6450. 8.5.2 eedr ? the eeprom data register ? bits 7:0 ? eedr7..0: eeprom data for the eeprom write operation, the eedr register contains the data to be written to the eeprom in the address given by the eear regi ster. for the eeprom read operation, the eedr contains the data read out from the eeprom at the add ress given by eear. 8.5.3 eecr ? the eeprom control register ? bits 7:4 ? reserved bits these bits are reserved bits in the atmel atmega325/3250/645/6450 and will always read as zero. ? bit 3 ? eerie: eeprom ready interrupt enable writing eerie to one enables the eeprom ready interrupt if the i bit in sreg is set. writing eerie to zero disables the interrupt. the eeprom ready interrupt generates a constant inter- rupt when eewe is cleared. bit 151413121110 9 8 0x22 (0x42) ? ? ? ? ? eear10 eear9 eear8 eearh 0x21 (0x41) eear7 eear6 eear5 eear4 eear3 eear2 eear1 eear0 eearl 76543210 read/write r r r r r r/w r/w r/w r/w r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 x x x xxxxxxxx bit 76543210 0x20 (0x40) msb lsb eedr read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 bit 76543210 0x1f (0x3f) ????eerieeemweeeweeereeecr read/write r r r r r/w r/w r/w r/w initial value000000x0 23 2570n?avr?05/11 atmega325/3250/645/6450 ? bit 2 ? eemwe: eeprom master write enable the eemwe bit determines whether setting eewe to one causes the eeprom to be written. when eemwe is set, setting eewe within four cl ock cycles will write data to the eeprom at the selected address if eemwe is zero, sett ing eewe will have no e ffect. when eemwe has been written to one by software, hardware clears th e bit to zero after four clock cycles. see the description of the eewe bit for an eeprom write procedure. ? bit 1 ? eewe: eeprom write enable the eeprom write enable signal eewe is the write strobe to the eeprom. when address and data are correctly set up, the eewe bit must be written to one to write the value into the eeprom. the eemwe bit must be written to one be fore a logical one is written to eewe, oth- erwise no eeprom write takes place. the following procedure should be followed when writing the eeprom (the order of steps 3 and 4 is not essential): 1. wait until eewe becomes zero. 2. wait until spmen in spmcsr becomes zero. 3. write new eeprom address to eear (optional). 4. write new eeprom data to eedr (optional). 5. write a logical one to the eemwe bit while writing a zero to eewe in eecr. 6. within four clock cycles after setting eemwe, write a logical one to eewe. the eeprom can not be programmed during a cpu write to the flash memory. the software must check that the flash programming is co mpleted before initiating a new eeprom write. step 2 is only relevant if the software contai ns a boot loader allowing the cpu to program the flash. if the flash is never being updated by the cpu, step 2 can be omitted. see ?boot loader support ? read-while-write self-programming? on page 251 for details about boot programming. caution: an interrupt between step 5 and step 6 will make the write cycle fail, since the eeprom master write enable will time-out. if an interrupt routine accessing the eeprom is interrupting another eeprom acce ss, the eear or eedr register will be modified, causing the interrupted eeprom access to fail. it is recommended to have the global interrupt flag cleared during all the steps to avoid these problems. when the write access time has elapsed, the eewe bit is cleared by hardware. the user soft- ware can poll this bit and wait for a zero before writing the next byte. when eewe has been set, the cpu is halted for two cycles before the next instruction is executed. ? bit 0 ? eere: eeprom read enable the eeprom read enable signal eere is the re ad strobe to the eeprom. when the correct address is set up in the eear register, the eere bit must be written to a logic one to trigger the eeprom read. the eeprom read access takes one instruction, and th e requested data is available immediately. when t he eeprom is read, the cpu is ha lted for four cycles before the next instruction is executed. the user should poll the eewe bit before starti ng the read operation. if a write operation is in progress, it is neither possi ble to read the eeprom, nor to change the eear register. the calibrated oscillator is used to time the eeprom accesses. table 8 -1 lists the typical pro- gramming time for eeprom access from the cpu. 24 2570n?avr?05/11 atmega325/3250/645/6450 the following code examples show one assembly and one c function for writing to the eeprom. the examples assume that interrupts are controlled (e.g. by dis abling interrupts glob- ally) so that no interrupts will occur during ex ecution of these functions. the examples also assume that no flash boot loader is present in the software. if such code is present, the eeprom write function must also wait fo r any ongoing spm command to finish. the next code examples show assembly and c functions for reading the eeprom. the exam- ples assume that interrupts are controlled so that no interrupts will occur during execution of these functions. table 8-1. eeprom programming time symbol number of calibrated rc oscillator cycles ty pical programming time eeprom write (from cpu) 27,072 3.4ms assembly code example eeprom_write: ; wait for completion of previous write sbic eecr,eewe rjmp eeprom_write ; set up address (r18:r17) in address register out eearh, r18 out eearl, r17 ; write data (r16) to data register out eedr,r16 ; write logical one to eemwe sbi eecr,eemwe ; start eeprom write by setting eewe sbi eecr,eewe ret c code example void eeprom_write( unsigned int uiaddress, unsigned char ucdata) { /* wait for completion of previous write */ while(eecr & (1< 27 2570n?avr?05/11 atmega325/3250/645/6450 9.1.4 asynchronous timer clock ? clk asy the asynchronous timer clock al lows the asynchronous timer/c ounter to be clocked directly from an external clock or an external 32khz clock crystal. the dedicated clock domain allows using this timer/counter as a real-time counter even when the device is in sleep mode. 9.1.5 adc clock ? clk adc the adc is provided with a dedicated clock domain. this allows halting the cpu and i/o clocks in order to reduce noise generated by digital circuitry. this gives more accurate adc conversion results. 9.2 clock sources the device has the following clock source options, selectable by flash fuse bits as shown below. the clock from the selected source is input to the avr clock generator, and routed to the appropriate modules. note: for all fuses ?1? means unprogrammed while ?0? means programmed. the various choices for each clocking option is given in the following sections. when the cpu wakes up from power-down or power-save, the selected clock source is used to time the start- up, ensuring stable osc illator operation bef ore instruction execution st arts. when the cpu starts from reset, there is an additional delay allowi ng the power to reach a stable level before com- mencing normal operation. the watchdog oscillator is used for timing this real-time part of the start-up time. the number of wd t oscillator cycles used for each time-out is shown in table 9-2 on page 27 . the frequency of the wa tchdog oscillator is voltag e dependent as shown in ?typi- cal characteristics? on page 306 . 9.2.1 default clock source the device is shipped with cksel = ?0010?, sut = ?10?, and ckdiv 8 programmed. the default clock source setting is the internal rc oscillator with longes t start-up time and an initial system clock prescaling of 8 . this default setting ensures that all users can make their desired clock source setting using an in-system or parallel programmer. table 9-1. device clocking options select (note:) device clocking option cksel3..0 external crystal/ceramic resonator 1111 - 1000 external low-frequency crystal 0111 - 0110 calibrated internal rc oscillator 0010 external clock 0000 reserved 0011, 0001, 0101, 0100 table 9-2. number of watchdog oscillator cycles typ time-out (v cc = 5.0v) typ time-out (v cc = 3.0v) number of cycles 4.1ms 4.3ms 4k (4,096) 65ms 69ms 64k (65,536) 28 2570n?avr?05/11 atmega325/3250/645/6450 9.3 crystal oscillator xtal1 and xtal2 are input and output, respectively, of an inverting amplifier which can be con- figured for use as an on-chip oscillator, as shown in figure 9-2 on page 2 8 . either a quartz crystal or a ceramic resonator may be used. c1 and c2 should always be equal for both crystals and resonators. the optimal value of the capacitors depends on the crystal or resonator in use, the amount of stray capacitance, and the electromagnetic noise of the environment. some initial guidelines for choosing capacitors for use with crystals are given in table 9-3 on page 2 8 . for ceramic resonators, the capacitor val- ues given by the manufacturer should be used. figure 9-2. crystal oscillator connections the oscillator can operate in three different mo des, each optimized for a specific frequency range. the operating mode is selected by the fuses cksel3..1 as shown in table 9-3 on page 2 8 . note: this option should not be used with crystals, only with ceramic resonators. the cksel0 fuse together with the sut1..0 fuses select the start-up times as shown in table 9-4 on page 2 8 . table 9-3. crystal oscillator operating modes cksel3:1 frequency range (mhz) recommended range for capacitors c1 and c2 for use with crystals (pf) 100 (note:) 0.4 - 0.9 ? 101 0.9 - 3.0 12 - 22 110 3.0 - 8 .0 12 - 22 111 8 .0 - 12 - 22 table 9-4. start-up times for the crysta l oscillator clock selection cksel0 sut1:0 start-up time from power-down and power-save additional delay from reset (v cc = 5.0v) recommended usage 000 25 8 ck (1) 14ck + 4.1ms ceramic resonator, fast rising power 001 25 8 ck (1) 14ck + 65ms ceramic resonator, slowly rising power 010 1k ck (2) 14ck ceramic resonator, bod enabled xtal2 xtal1 gnd c2 c1 29 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. these options should only be used when no t operating close to the maximum frequency of the device, and only if frequency stability at start- up is not important for the application. these options are not suitable for crystals. 2. these options are intended for use with cerami c resonators and will ensure frequency stability at start-up. they can also be used with crystal s when not operating close to the maximum fre- quency of the device, and if frequency stability at start-up is not important for the application. 9.4 low-frequency crystal oscillator to use a 32.76 8 khz watch crystal as the clock source for the device, the low-frequency crystal oscillator must be selected by se tting the cksel fuses to ?0110? or ?0111?. th e crystal should be connected as shown in figure 9-2 on page 2 8 . when this oscillator is selected, start-up times are determined by the sut fuses as shown in table 9-5 on page 29 and cksel1..0 as shown in table 9-6 on page 29 . note: this option should only be used if frequency stability at start-up is not important for the application 9.5 calibrated internal rc oscillator the calibrated internal rc osc illator by default provides a 8 .0mhz clock. the frequency is nom- inal value at 3v and 25c. the device is shipped with the ckdiv 8 fuse programmed. see ?system clock prescaler? on page 32 for more details. 011 1k ck (2) 14ck + 4.1ms ceramic resonator, fast rising power 100 1k ck (2) 14ck + 65ms ceramic resonator, slowly rising power 1 01 16k ck 14ck crystal oscillator, bod enabled 1 10 16k ck 14ck + 4.1ms crystal oscillator, fast rising power 1 11 16k ck 14ck + 65ms crystal oscillator, slowly rising power table 9-4. start-up times for the crystal osc illator clock select ion (continued) cksel0 sut1:0 start-up time from power-down and power-save additional delay from reset (v cc = 5.0v) recommended usage table 9-5. start-up times for the lo w-frequency crystal os cillator clock selection sut1..0 additional delay from reset (v cc = 5.0v) recommended usage 00 14ck fast rising power or bod enabled 01 14ck + 4.1ms slowly rising power 10 14ck + 65ms stable frequency at start-up 11 reserved table 9-6. start-up times for the lo w-frequency crystal os cillator clock selection cksel3..0 start-up time from power-down and power-save recommended usage 0110 (note:) 1k ck 0111 32k ck stable frequency at start-up 30 2570n?avr?05/11 atmega325/3250/645/6450 this clock may be selected as the system clock by programming the cksel fuses as shown in table 9-7 on page 30 . if selected, it will operate with no external components. during reset, hardware loads the pre-programmed calibration value into the osccal register and thereby automatically calibrates the rc oscillator. the a ccuracy of this calibration is shown as factory calibration in table 2 8 -2 on page 300 . by changing the osccal register from sw, see ?osccal ? oscillator ca libration register? on page 32 , it is possible to get a higher calibration accuracy than by using the factory calibration. the accuracy of this calibration is shown as user calibration in table 2 8 -2 on page 300 . when this oscillator is used as the chip clock, the watchdog oscillator will still be used for the watchdog timer and for the reset time-out. for more information on the pre-programmed cali- bration value, see the section ?calibration byte? on page 26 8 . note: 1. the device is shipped with this option selected. 2. the frequency ranges are preliminary values. actual values are tbd. 3. if 8 mhz frequency exceeds the specification of the device (depends on v cc ), the ckdiv 8 fuse can be programmed in order to divide the internal frequency by 8 . when this oscillator is select ed, start-up times are determined by the sut fuses as shown in table 9- 8 on page 30 . note: the device is shipped with this option selected. 9.6 external clock to drive the device from an external clock source, xtal1 should be driven as shown in figure 9-3 on page 31 . to run the device on an external cloc k, the cksel fuses must be programmed to ?0000? (see table 9-9 on page 30 ). table 9-7. internal calibrated rc o scillator operating modes (1)(3) frequency range (2) (mhz) cksel3..0 7.3 - 8 .1 0010 table 9-8. start-up times for the internal calib rated rc oscillator clock selection power conditions start-up time from power- down and power-save additional delay from reset (v cc = 5.0v) sut1..0 bod enabled 6 ck 14ck 00 fast rising power 6 ck 14ck + 4.1ms 01 slowly rising power 6 ck 14ck + 65ms (note:) 10 reserved 11 table 9-9. crystal oscillator clock frequency frequency range cksel3..0 0 - 16mhz 0000 31 2570n?avr?05/11 atmega325/3250/645/6450 figure 9-3. external clock drive configuration when this clock source is sele cted, start-up times are determined by the sut fuses as shown in table 9-10 on page 31 . when applying an external clock, it is required to avoid sudden changes in the applied clock fre- quency to ensure stable operation of the mcu. a variation in frequency of more than 2% from one clock cycle to the next can lead to unpredictable behavior. it is required to en sure that the mcu is kept in reset during such changes in the clock frequency. note that the system clock prescaler can be used to implement run-time changes of the internal clock frequency while still ensuri ng stable operation. refer to ?system clock prescaler? on page 32 for details. 9.7 clock output buffer when the ckout fuse is prog rammed, the system clock will be ou tput on clko. this mode is suitable when the chip clock is used to drive othe r circuits on the system. the clock will be out- put also during reset and the normal opera tion of i/o pin will be overridden when the fuse is programmed. any clock source, including internal rc oscillator, can be selected when clko serves as clock output. if the system clock prescaler is used, it is the divided system clock that is output when the ckout fuse is programmed. 9.8 timer/counter oscillator atmel atmega325/3250/645/6450 share the timer/ counter oscillator pins (tosc1 and tosc2) with xtal1 and xtal2. th is means that the ti mer/counter o scillator can only be used when the calibrated internal rc oscillator is se lected as system clock s ource. the oscillator is optimized for use with a 32.76 8 khz watch crystal. see figure 9-2 on page 2 8 for crystal connection. table 9-10. start-up times for the external clock selection sut1..0 start-up time from power- down and power-save additional delay from reset (v cc = 5.0v) recommended usage 00 6 ck 14ck bod enabled 01 6 ck 14ck + 4.1ms fast rising power 10 6 ck 14ck + 65ms slowly rising power 11 reserved nc external clock signal xtal2 xtal1 gnd 32 2570n?avr?05/11 atmega325/3250/645/6450 applying an external clock source to tosc1 c an be done if extclk in the assr register is written to logic one. see ?asynchronous operation of timer/counter2? on page 141 for further description on selecting external clo ck as input instead of a 32khz crystal. 9.9 system clock prescaler the atmel atmega325/3250/645/6450 system clock can be divided by setting the ?clkpr ? clock prescale register? on page 33 . this feature can be used to decrease power consumption when the requirement for processing power is low. this can be used with all clock source options, and it will affect the clock frequency of the cpu and all synchronous peripherals. clk i/o , clk adc , clk cpu , and clk flash are divided by a factor as shown in table 9-11 on page 33 . 9.9.1 switching time when switching between prescaler settings, the system clock prescaler ensures that no glitches occur in the clock system and that no intermediate frequency is higher than neither the clock frequency corresponding to the previous setting, nor the clock frequency corresponding to the new setting. the ripple counter that implements the prescaler runs at the frequency of the undivided clock, which may be faster than the cpu?s clock frequency. hence, it is not possible to determine the state of the prescaler ? even if it were readable, and the exact time it takes to switch from one clock division to another cannot be exactly predicted. from the time the clkps values ar e written, it takes between t1 + t2 and t1 + 2*t2 before the new clock frequency is active. in this interval, 2 active clock edges are produced. here, t1 is the previous clock period, and t2 is the period corresponding to the new prescaler setting. 9.10 register description 9.10.1 osccal ? oscillato r calibration register ? bits 7:0 ? cal7:0: oscillator calibration value the oscillator calibration register is used to trim the calibrated internal rc oscillator to remove process variations from the oscillator frequency. a pre-programmed calibration value is automatically written to this register during chip reset, giving the factory calibrated frequency as specified in table 2 8 -2 on page 300 . the application software can write this register to change the oscillator frequency. the os cillator can be calibrated to frequencies as specified in table 2 8 - 2 on page 300 . calibration outside that range is not guaranteed. note that this o scillator is used to time eeprom and flash write accesses , and these write times will be affected accordingly. if the eeprom or flash are writ ten, do not calibrate to more than 8 . 8 mhz. otherwise, the eeprom or flash write may fail. the cal7 bit determines the range of operation for the oscillator. setting this bit to 0 gives the lowest frequency range, setting this bit to 1 gives the highest frequency range. the two fre- quency ranges are overlapping, in other words a setting of osccal = 0x7f gives a higher frequency than osccal = 0x 8 0. bit 76543210 (0x66) cal7 cal6 cal5 cal4 cal3 cal2 cal1 cal0 osccal read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value device spec ific calibration value 33 2570n?avr?05/11 atmega325/3250/645/6450 the cal6..0 bits are used to tune the frequency within the selected range. a setting of 0x00 gives the lowest frequency in that range, and a setting of 0x7f gives the highest frequency in the range. 9.10.2 clkpr ? clock prescale register ? bit 7 ? clkpce: clock prescaler change enable the clkpce bit must be written to logic one to enab le change of the clkps bits. the clkpce bit is only updated when the other bits in cl kpr are simultaneously wr itten to zero. clkpce is cleared by hardware four cycles af ter it is written or when clkps bits are written. rewriting the clkpce bit within this time-out period does neither extend the time-out period, nor clear the clkpce bit. ? bits 3:0 ? clkps3:0: clock prescaler select bits 3 - 0 these bits define the division factor between the selected clock source and the internal system clock. these bits can be written run-time to vary the clock frequency to suit the application requirements. as the divider divides the master clock input to the mcu, the speed of all synchro- nous peripherals is reduced when a division fact or is used. the division factors are given in table 9-11 on page 33 . to avoid unintentional changes of clock frequency, a special write procedure must be followed to change the clkps bits: 1. write the clock prescaler change enable (clkpce) bit to one and all other bits in clkpr to zero. 2. within four cycles, write the desired value to clkps while writing a zero to clkpce. interrupts must be disabled when changing prescaler setting to make sure the write procedure is not interrupted. the ckdiv 8 fuse determines the initial value of the clkps bits. if ckdiv 8 is unprogrammed, the clkps bits will be reset to ?0000?. if ckdiv 8 is programmed, clkps bits are reset to ?0011?, giving a division factor of 8 at start up. this feature should be used if the selected clock source has a higher frequency than the maximum frequency of the device at the present operat- ing conditions. note that any value can be written to the clkps bits regardless of the ckdiv 8 fuse setting. the application software must ensure that a sufficient division factor is chosen if the selected clock source has a higher frequency than the maximum frequency of the device at the present operating conditions. the device is shipped with the ckdiv 8 fuse programmed. bit 76543210 (0x61) clkpce ? ? ? clkps3 clkps2 clkps1 clkps0 clkpr read/write r/w r r r r/w r/w r/w r/w initial value 0 0 0 0 see bit description table 9-11. clock prescaler select clkps3 clkps2 clk ps1 clkps0 clock division factor 0000 1 0001 2 0010 4 0011 8 0100 16 34 2570n?avr?05/11 atmega325/3250/645/6450 0101 32 0110 64 0111 12 8 1000 256 1001 reserved 1010 reserved 1011 reserved 1100 reserved 1101 reserved 1110 reserved 1111 reserved table 9-11. clock prescaler select clkps3 clkps2 clk ps1 clkps0 clock division factor 35 2570n?avr?05/11 atmega325/3250/645/6450 10. power management and sleep modes sleep modes enable the application to shut down unused modules in the mcu, thereby saving power. the avr provides various sleep modes allowing the user to tailor the power consump- tion to the application?s requirements. 10.1 sleep modes figure 9-1 on page 26 presents the different clock systems in the atmel atmega325/3250/645/6450, and their distribution. the figure is helpful in selecting an appropri- ate sleep mode. table 10-1 on page 35 shows the different sleep modes and their wake up sources. note: 1. only recommended with external crystal or resonator selected as clock source. 2. if timer/counter2 is running in asynchronous mode. 3. for int0, only level interrupt. to enter any of the five sleep modes, the se bit in smcr must be written to logic one and a sleep instruction must be executed. the sm2, sm1, and sm0 bits in the smcr register select which sleep mode (idle, adc noise reduction, power-down, power-save, or standby) will be activated by the sleep instruction. see table 10-2 on page 39 for a summary. if an enabled interrupt occurs while the mcu is in a sleep mode, the mcu wakes up. the mcu is then halted for four cycles in addition to the st art-up time, executes the interrupt routine, and resumes execution from the instruction followi ng sleep. the contents of the register file and sram are unaltered when the device wakes up from sleep. if a reset occurs during sleep mode, the mcu wakes up and executes from the reset vector. 10.2 idle mode when the sm2..0 bits are written to 000, the sleep instruction makes the mcu enter idle mode, stopping the cpu but allowing the spi, usart, analog comparator, adc, usi, timer/counters, watchdog, and the interrupt system to continue operating. this sleep mode basically halts clk cpu and clk flash , while allowing the other clocks to run. idle mode enables the mcu to wake up from external triggered interrupts as well as internal ones like the timer overflow and usart transmit complete interrupts. if wake-up from the table 10-1. active clock domains and wake-up sour ces in the different sleep modes. active clock domains oscillators wake-up sources sleep mode clk cpu clk flash clk io clk adc clk asy main clock source enabled timer osc enabled int0 and pin change usi start condition timer2 spm/eeprom ready adc other i/o idle x x x x x (2) xxxxxx adc noise reduction x x x x (2) x (3) xx (2) xx power-down x (3) x power-save x x (2) x (3) xx standby (1) xx (3) x 36 2570n?avr?05/11 atmega325/3250/645/6450 analog comparator interrupt is not required, the analog comparator can be powered down by setting the acd bit in the analog comparator control and status regist er ? acsr. this will reduce power consumption in idle mode. if t he adc is enabled, a conversion starts automati- cally when this mode is entered. 10.3 adc noise reduction mode when the sm2..0 bits are written to 001, the sleep instruction makes the mcu enter adc noise reduction mode, stopping the cpu but allowi ng the adc, the external interrupts, the usi start condition detection, timer/counter2, and the watchdog to continue operating (if enabled). this sleep mode basically halts clk i/o , clk cpu , and clk flash , while allowing the other clocks to run. this improves the noise environment for the ad c, enabling higher resolution measurements. if the adc is enabled, a conversion starts automatically when this mode is entered. apart form the adc conversion complete interrupt, only an external reset, a watchdog reset, a brown-out reset, a usi start condition interrupt, a timer/counter2 interrupt, an spm/eeprom ready inter- rupt, an external level interrupt on int0 or a pin change interrupt can wake up the mcu from adc noise reduction mode. 10.4 power-down mode when the sm2..0 bits are written to 010, the sleep instruction makes the mcu enter power- down mode. in this mode, the external oscillator is stopped, while the external interrupts, the usi start condition detection, and the watchdog continue operating (if enabled). only an exter- nal reset, a watchdog reset, a brown-out reset, usi start condition interrupt, an external level interrupt on int0, or a pin change interrupt can wake up the mcu. this sleep mode basically halts all generated clocks, allowing operation of asynchronous modules only. note that if a level triggered interrupt is used for wake-up from power-down mode, the changed level must be held for some time to wake up the mcu. refer to ?external interrupts? on page 55 for details. when waking up from power-down mode, there is a delay from the wake-up condition occurs until the wake-up becomes effective. this allows the clock to restart and become stable after having been stopped. the wake-up period is defined by the same cksel fuses that define the reset time-out period, as described in ?clock sources? on page 27 . 10.5 power-save mode when the sm2..0 bits are written to 011, the sleep instruction makes the mcu enter power- save mode. this mode is identical to power-down, with one exception: if timer/counter2 controller is en abled, it will keep running dur ing sleep. the device can wake up from either timer overflow or output compare event from timer/counter2 if the correspond- ing timer/counter2 interrupt enable bits are se t in timsk2, and the global interrupt enable bit in sreg is set. if the timer/counter2 is not running, power-down mode is recommended instead of power-save mode. the timer/counter2 can be clocked both synchronously and asynchronously in power-save mode. if timer/counter2 is no t using the asynchronous clock, the timer/counter oscillator is stopped during sleep. if timer/counter2 is not using the synchronous cloc k, the clock source is stopped during sleep. note that even if the synchronous clock is running in power-save, this clock is only available for timer/counter2. 37 2570n?avr?05/11 atmega325/3250/645/6450 10.6 standby mode when the sm2..0 bits are 110 and an external crystal/resonator clock option is selected, the sleep instruction makes the mcu enter standby mode. this mode is identical to power-down with the exception that the oscillator is kept running. fr om standby mode, the device wakes up in six clock cycles. 10.7 power reduction register the power reduction register (prr), see ?prr ? power reduction register? on page 40 , pro- vides a method to stop the clock to individual per ipherals to reduce power consumption. the current state of the peripheral is frozen and the i/o registers inaccessible. resources used by the peripheral when stopping the clock will remain occupied so the periphe ral should be disabled before stopping the clock. waking up a peripheral, which is done by clearing the bit in prr, puts the peripheral in the same state as before shutdown. peripheral shutdown can be used in idle mode and active mode to reduce the overall power consumption. in all other sleep modes, the clock is already stopped. 10.8 minimizing power consumption there are several possibilities to consider when trying to minimi ze the power consumption in an avr controlled system. in general, sleep modes should be used as much as possible, and the sleep mode should be selected so that as few as possible of the device?s functions are operat- ing. all functions not needed shoul d be disabled. in particular, the following modules may need special consideration when trying to achieve the lowest possible power consumption. 10.8.1 analog to digital converter if enabled, the adc will be enabled in all sleep modes. to save power, the adc should be dis- abled before entering any sleep mode. when the adc is turned off and on again, the next conversion will be an extended conversion. refer to ?analog to digital converter? on page 201 for details on adc operation. 10.8.2 analog comparator when entering idle mode, the analog comparator should be disabled if not used. when entering adc noise reduction mode, the analog comparator should be disabled. in other sleep modes, the analog comparator is automatically disabled. however, if the analog comparator is set up to use the internal voltage reference as input, the analog comparator should be disabled in all sleep modes. otherwise, the internal voltage reference will be enabled, independent of sleep mode. refer to ?analog comparator? on page 197 for details on how to configure the analog comparator. 10.8.3 brown-out detector if the brown-out detector is not needed by the application, this module should be turned off. if the brown-out detector is enabled by the bo dlevel fuses, it will be enabled in all sleep modes, and hence, always co nsume power. in the deeper sleep modes, this w ill contribute sig- nificantly to the total current consumption. refer to ?brown-out detect ion? on page 43 for details on how to configure the brown-out detector. 10.8.4 internal voltage reference the internal voltage referenc e will be enabled when needed by the brown-out de tection, the analog comparator or the adc. if these modules are disabled as described in the sections 38 2570n?avr?05/11 atmega325/3250/645/6450 above, the internal voltage refe rence will be disabled and it w ill not be consuming power. when turned on again, the user must allow the reference to start up before the output is used. if the reference is kept on in sleep mode, the output can be used immediately. refer to ?internal volt- age reference? on page 44 for details on the start-up time. 10.8.5 watchdog timer if the watchdog timer is not needed in the application, the module should be turned off. if the watchdog timer is enabled, it will be enabled in all sleep modes, and hence, always consume power. in the deeper slee p modes, this will contribute signific antly to the total current consump- tion. refer to ?watchdog timer? on page 45 for details on how to configure the watchdog timer. 10.8.6 port pins when entering a sleep mode, all port pins should be configured to use minimum power. the most important is then to ensure that no pins drive resistive loads. in sleep modes where both the i/o clock (clk i/o ) and the adc clock (clk adc ) are stopped, the input buf fers of the device will be disabled. this ensures that no power is consumed by the input logic when not needed. in some cases, the input logic is needed for detec ting wake-up conditions, and it will then be enabled. refer to the section ?digital input enable and sleep modes? on page 65 for details on which pins are enabled. if the input buffer is enabl ed and the input signal is left floating or have an analog signal level close to v cc /2, the input buffer will use excessive power. for analog input pins, the digital input buffer should be disabled at all times. an analog signal level close to v cc /2 on an input pin can cause significant current even in active mode. digital input buffers can be disabled by writing to the digital input disable registers (didr1 and didr0). refer to ?didr1 ? digital input disable register 1? on page 200 and ?didr0 ? digital input disable register 0? on page 217 for details. 10.8.7 jtag interface and on-chip debug system if the on-chip debug system is enabled by the ocden fuse and the chip enter power down or power save sleep mode, the main clock source remains enabled. in these sl eep modes, this will contribute significantly to the total current c onsumption. there are three alternative ways to avoid this: ? disable ocden fuse. ? disable jtagen fuse. ? write one to the jtd bit in mcucsr. the tdo pin is left floating when the jtag interf ace is enabled while th e jtag tap controller is not shifting data. if the hardware connected to t he tdo pin does not pull up the logic level, power consumption will increase. note that the tdi pin fo r the next device in the scan chain con- tains a pull-up that avoids this problem. writi ng the jtd bit in the mcucsr register to one or leaving the jtag fuse unprogrammed disables the jtag interface. 39 2570n?avr?05/11 atmega325/3250/645/6450 10.9 register description 10.9.1 smcr ? sleep m ode control register the sleep mode control register contains control bits for power management. ? bits 3, 2, 1 ? sm2:0: sleep mode select bits 2, 1, and 0 these bits select between the five available sleep modes as shown in table 10-2 . note: 1. standby mode is only recommended for use with external crystals or resonators. ? bit 1 ? se: sleep enable the se bit must be written to logic one to make the mcu enter the sleep mode when the sleep instruction is executed. to avoid the mcu enteri ng the sleep mode unless it is the programmer?s purpose, it is recommended to write the sleep enable (se) bit to one just before the execution of the sleep instruction and to clear it immediately af ter waking up. bit 76543210 0x33 (0x53) ? ? ? ? sm2 sm1 sm0 se smcr read/write r r r r r/w r/w r/w r/w initial value00000000 table 10-2. sleep mode select sm2 sm1 sm0 sleep mode 000idle 0 0 1 adc noise reduction 010power-down 011power-save 100reserved 101reserved 110standby (1) 111reserved 40 2570n?avr?05/11 atmega325/3250/645/6450 10.9.2 prr ? power reduction register ? bits 7:4 - reserved bits these bits are reserved bits in atmel atmeg a325/3250/645/ 6450 and will always read as zero. ? bit 3 - prtim1: power reduction timer/counter1 writing logic one to this bit shuts down the timer/counter1 module. when timer/counter1 is enabled, operation will continue like before the shutdown. ? bit 2 - prspi: power reduction serial peripheral interface writing logic one to this bit shuts down the seri al peripheral interface by stopping the clock to the module. when waking up the spi again, the spi should be re-initialized to ensure proper operation. ? bit 1 - prusart: power reduction usart writing logic one to this bit shuts down the usart by stopping the clock to the module. when waking up the usart again, the usart should be re-initialized to ensure proper operation. ? bit 0 - pradc: power reduction adc writing logic one to this bit shuts down the a dc. the adc must be disabled before shut down. the analog comparator cannot use the adc input mux when the adc is shut down. the analog comparator is disabled using the acd-bit in the ?acsr ? analog compar ator control and sta- tus register? on page 19 8 . bit 7654 3 2 1 0 (0x64) ? ? ? ? prtim1 prspi prusart0 pradc prr read/write r r r r r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 41 2570n?avr?05/11 atmega325/3250/645/6450 11. system control and reset 11.1 resetting the avr during reset, all i/o registers are set to their initial values, and the program starts execution from the reset vector. the instruction placed at the reset vector must be a jmp ? absolute jump ? instruction to the reset handling routine. if the program never enables an interrupt source, the interrupt vectors are not used, and regular program code can be placed at these locations. this is also the case if the reset vector is in the app lication section while the interrupt vectors are in the boot section or vice versa. the circuit diagram in figure 11-1 on page 42 shows the reset logic. table 2 8 -4 on page 301 defines the electrical parameters of the reset circuitry. the i/o ports of the avr are immediately reset to their initial state when a reset source goes active. this does not require any clock source to be running. after all reset sources have gone inactive, a delay counter is invoked, stretching the internal reset. this allows the power to reach a stable level before normal operation starts. the time-out period of the delay counter is defined by the user through the sut and cksel fuses. the dif- ferent selections for the delay period are presented in ?clock sources? on page 27 . 11.2 reset sources the atmel atmega325/3250/645/6450 has five sources of reset: ? power-on reset. the mcu is reset when the supply voltage is be low the power-on reset threshold (v pot ). ? external reset. the mcu is reset wh en a low level is present on the reset pin for longer than the minimum pulse length. ? watchdog reset. the mcu is reset when the watchdog timer period expires and the watchdog is enabled. ? brown-out reset. the mcu is reset when the supply voltage v cc is below the brown-out reset threshold (v bot ) and the brown-out detector is enabled. ? jtag avr reset. the mcu is reset as long as there is a logic one in the reset register, one of the scan chains of the jtag system. refer to the section ?ieee 1149.1 (jtag) boundary-scan? on page 224 for details. 42 2570n?avr?05/11 atmega325/3250/645/6450 figure 11-1. reset logic 11.3 power-on reset a power-on reset (por) pulse is generated by an on-chip detection circuit. the detection level is defined in ?system and reset characteristics? on page 301 . the por is activated whenever v cc is below the detection level. the por circuit can be used to trigger the start-up reset, as well as to detect a fa ilure in supply voltage. a power-on reset (por) circuit ensures that the device is reset from power-on. reaching the power-on reset threshold voltage invokes the delay counter, which determines how long the device is kept in reset after v cc rise. the reset signal is acti vated again, without any delay, when v cc decreases below the detection level. figure 11-2. mcu start-up, reset tied to v cc mcu status register (mcusr) brown-out reset circuit bodlevel [1..0] delay counters cksel[3:0] ck timeout wdrf borf extrf porf data b u s clock generator spike filter pull-up resistor jtrf jtag reset register watchdog oscillator sut[1:0] power-on reset circuit v reset time-out internal reset t tout v pot v rst cc 43 2570n?avr?05/11 atmega325/3250/645/6450 figure 11-3. mcu start-up, reset extended externally 11.4 external reset an external reset is generated by a low level on the reset pin. reset pulses longer than the minimum pulse width (see ?system and reset characteristics? on page 301 ) will generate a reset, even if the clock is not running. shorter pulses are not guaranteed to generate a reset. when the applied signal reaches the reset threshold voltage ? v rst ? on its positive edge, the delay counter starts the mcu after the time-out period ? t tout ? has expired. figure 11-4. external reset during operation 11.5 brown-out detection atmel atmega325/3250/645/6450 has an on-chip brown- out detection (bod) circuit for moni- toring the v cc level during operation by comparing it to a fixed trigger level. the trigger level for the bod can be selected by the bodlevel fu ses. the trigger level ha s a hysteresis to ensure spike free brown-out detection. the hysteresis on the detection level should be interpreted as v bot+ = v bot + v hyst /2 and v bot- = v bot - v hyst /2. when the bod is enabled, and v cc decreases to a value below the trigger level (v bot- in figure 11-5 on page 44 ), the brown-out reset is immediately activated. when v cc increases above the trigger level (v bot+ in figure 11- 5 on page 44 ), the delay counter starts the mcu after the time-out period t tout has expired. the bod circuit will only detect a drop in v cc if the voltage stays below the trigger level for lon- ger than t bod given in ?system and reset characteristics? on page 301 . reset time-out internal reset t tout v pot v rst v cc cc 44 2570n?avr?05/11 atmega325/3250/645/6450 figure 11-5. brown-out reset during operation 11.6 watchdog reset when the watchdog times out, it will generate a short reset pulse of one ck cycle duration. on the falling edge of this pulse, the delay timer starts counting the time-out period t tout . refer to page 45 for details on operation of the watchdog timer. figure 11-6. watchdog reset during operation 11.7 internal voltage reference atmel atmega325/3250/645/6450 features an internal bandgap reference. this reference is used for brown-out detection, and it can be used as an input to the analog comparator or the adc. 11.7.1 voltage reference enable signals and start-up time the voltage reference has a start-up time that may influence the way it should be used. the start-up time is given in ?system and reset characteristics? on page 301 . to save power, the reference is not always turned on. the reference is on during the following situations: 1. when the bod is enabled (by pr ogramming the bodlevel [1..0] fuse). 2. when the bandgap reference is connected to the analog comparator (by setting the acbg bit in acsr). 3. when the adc is enabled. v cc reset time-out internal reset v bot- v bot+ t tout ck cc 45 2570n?avr?05/11 atmega325/3250/645/6450 thus, when the bod is not enabled, after setting the acbg bit or enabling the adc, the user must always allow the reference to start up before the output from the analog comparator or adc is used. to reduce power consumption in power-down mode, the user can avoid the three conditions above to ensure that the reference is turned off before entering power-down mode. 11.8 watchdog timer the watchdog timer is clocked fr om a separate on-chip oscillato r which runs at 1 mhz. this is the typical value at v cc = 5v. see characterization data for typical values at other v cc levels. by controlling the watchdog timer prescaler, the watchdog reset interval can be adjusted as shown in table 11-2 on page 46 . the wdr ? watchdog reset ? instruction resets the watch- dog timer. the watchdog timer is also reset when it is disabled and when a chip reset occurs. eight different clock cycle periods can be selected to determine the reset period. if the reset period expires without another watchdog reset, the atmel atmega325/3250/645/6450 resets and executes from the reset vector. for timing details on the watchdog reset, refer to table 11-2 on page 46 . to prevent unintentional disabling of the watchdog or unintentional change of time-out period, two different safety levels are selected by the fuse wdton as shown in table 11-1. refer to ?timed sequences for changing the configuration of the watchdog timer? on page 46 for details. figure 11-7. watchdog timer table 11-1. wdt configuration as a function of the fuse settings of wdton wdton safety level wdt initial state how to disable the wdt how to change time-out unprogrammed 1 disabled timed sequence timed sequence programmed 2 enabled always enabled timed sequence watchdog oscillator 46 2570n?avr?05/11 atmega325/3250/645/6450 the following code example shows one assembly and one c function for turning off the wdt. the example assumes that interrupts are controlled (e.g. by disabling interrupts globally) so that no interrupts will occur during execution of these functions. note: 1. see ?about code examples? on page 9 . 11.9 timed sequences for c hanging the configuration of the watchdog timer the sequence for changing configuration differs slightly between the two safety levels. separate procedures are described for each level. table 11-2. watchdog timer prescale select wdp2 wdp1 wdp0 number of wdt oscillator cycles typical time-out at v cc = 3.0v typical time-out at v cc = 5.0v 0 0 0 16k cycles 17.1ms 16.3ms 0 0 1 32k cycles 34.3ms 32.5ms 0 1 0 64k cycles 6 8 .5ms 65ms 011 12 8 k cycles 0.14s 0.13s 1 0 0 256k cycles 0.27s 0.26s 1 0 1 512k cycles 0.55s 0.52s 1 1 0 1,024k cycles 1.1s 1.0s 111 2,04 8 k cycles 2.2s 2.1s assembly code example (1) wdt_off: ; reset wdt wdr ; write logical one to wdce and wde in r16, wdtcr ori r16, (1< 48 2570n?avr?05/11 atmega325/3250/645/6450 to make use of the reset flags to identify a reset condition, the user should read and then reset the mcusr as early as possible in the program. if the register is cleared before another reset occurs, the source of the reset can be found by examining the reset flags. 11.10.2 wdtcr ? watchdog timer control register ? bits 7:5 ? reserved bits these bits are reserved bits in the atmel atmega325/3250/645/6450 and will always read as zero. ? bit 4 ? wdce: watchdog change enable this bit must be set when the wde bit is writte n to logic zero. otherwis e, the watchdog will not be disabled. once written to one, hardware will clear this bit after four clock cycles. refer to the description of the wde bit for a watchdog disable procedure. this bit must also be set when changing the prescaler bits. see ?timed sequences for changing the configuration of the watchdog timer? on page 46. ? bit 3 ? wde: watchdog enable when the wde is written to logic one, the watchdog timer is enabled, and if the wde is written to logic zero, the watchdog timer function is di sabled. wde can only be cleared if the wdce bit has logic level one. to disable an enabled watchdog timer, the following procedure must be followed: 1. in the same operation, write a logic one to wdce and wde. a logic one must be written to wde even though it is set to one before the disable operation starts. 2. within the next four clock cycles, write a logic 0 to wde. this disables the watchdog. in safety level 2, it is not possible to disable the watchdog timer, even with the algorithm described above. see ?timed sequences for changing the configuration of the watchdog timer? on page 46. ? bits 2:0 ? wdp2, wdp1, wdp0: watchdog timer prescaler 2, 1, and 0 the wdp2, wdp1, and wdp0 bits determine the watchdog timer prescaling when the watch- dog timer is enabled. the different prescaling va lues and their corresponding time-out periods are shown in table 11-2 on page 46 . bit 76543210 (0x60) ? ? ? wdce wde wdp2 wdp1 wdp0 wdtcr read/write r r r r/w r/w r/w r/w r/w initial value00000000 49 2570n?avr?05/11 atmega325/3250/645/6450 12. interrupts this section describes the specifics of the interrupt handling as performed in atmel atmega325/3250/645/6450. for a general explanation of the avr interrupt handling, refer to ?reset and interrupt handling? on page 15 . 12.1 interrupt vectors in atmel atmega325/3250/645/6450 note: 1. when the bootrst fuse is prog rammed, the device will jump to the boot loader address at reset, see ?boot loader sup- port ? read-while-write self-programming? on page 251 . 2. when the ivsel bit in mcucr is set, interrupt vectors will be moved to the start of the boot flash section. the address of each interrupt vector will then be the address in this table added to the start address of the boot flash section. 3. pcint2 and pcint3 are only present in atmega3250 and atmega6450. table 12-1. reset and interrupt vectors vector no. program address (2) source interrup t definition 1 0x0000 (1) reset external pin, power-on reset, brown-out reset, watchdog reset, and jtag avr reset 2 0x0002 int0 external interrupt request 0 3 0x0004 pcint0 pin change interrupt request 0 4 0x0006 pcint1 pin change interrupt request 1 5 0x000 8 timer2 comp timer/counter2 compare match 6 0x000a timer2 ovf timer/counter2 overflow 7 0x000c timer1 capt timer/counter1 capture event 8 0x000e timer1 compa timer/counter1 compare match a 9 0x0010 timer1 compb timer /counter1 compare match b 10 0x0012 timer1 ovf timer/counter1 overflow 11 0x0014 timer0 comp timer/counter0 compare match 12 0x0016 timer0 ovf timer/counter0 overflow 13 0x001 8 spi, stc spi serial transfer complete 14 0x001a usart, rx usart, rx complete 15 0x001c usart, udre usart data register empty 16 0x001e usart, tx usart, tx complete 17 0x0020 usi start usi start condition 1 8 0x0022 usi overflow usi overflow 19 0x0024 analog comp analog comparator 20 0x0026 adc adc conversion complete 21 0x002 8 ee ready eeprom ready 22 0x002a spm ready store program memory ready 23 0x002c not_used reserved 24 (3) 0x002e pcint2 pin change interrupt request 2 25 (3) 0x0030 pcint3 pin change interrupt request 3 50 2570n?avr?05/11 atmega325/3250/645/6450 table 12-2 on page 50 shows reset and interrupt vectors placement for the various combina- tions of bootrst and ivsel settings. if the program never enables an interrupt source, the interrupt vectors are not used, and regular program code can be placed at these locations. this is also the case if the reset vector is in the application section while the interrupt vectors are in the boot section or vice versa. note: the boot reset address is shown in table 26-6 on page 262 . for the bootrst fuse ?1? means unprogrammed while ?0? means programmed. the most typical and general program setup for the reset and interrupt vector addresses in atmel atmega325/3250/645/6450 is: table 12-2. reset and interrupt vectors placement (note:) bootrst ivsel reset address interr upt vectors start address 1 0 0x0000 0x0002 1 1 0x0000 boot reset address + 0x0002 0 0 boot reset address 0x0002 0 1 boot reset address boot reset address + 0x0002 addre ss label s code comments 0x000 0 jmp reset ; reset handler 0x000 2 jmp ext_int0 ; irq0 handler 0x000 4 jmp pcint0 ; pcint0 handler 0x000 6 jmp pcint1 ; pcint1 handler 0x000 8 jmp tim2_comp ; timer2 compare handler 0x000 a jmp tim2_ovf ; timer2 overflow handler 0x000 c jmp tim1_capt ; timer1 capture handler 0x000 e jmp tim1_compa ; timer1 comparea handler 0x001 0 jmp tim1_compb ; timer1 compareb handler 0x001 2 jmp tim1_ovf ; timer1 overflow handler 0x001 4 jmp tim0_comp ; timer0 compare handler 0x001 6 jmp tim0_ovf ; timer0 overflow handler 0x001 8 jmp spi_stc ; spi transfer complete handler 0x001 a jmp usart_rxc ; usart rx complete handler 0x001 c jmp usart_udre ; usart,udr empty handler 0x001 e jmp usart_txc ; usart tx complete handler 0x002 0 jmp usi_strt ; usi start condition handler 51 2570n?avr?05/11 atmega325/3250/645/6450 0x002 2 jmp usi_ovf ; usi overflow handler 0x002 4 jmp ana_comp ; analog comparator handler 0x002 6 jmp adc ; adc conversion complete handler 0x002 8 jmp ee_rdy ; eeprom ready handler 0x002 a jmp spm_rdy ; spm ready handler 0x002 c ;not_used ; reserved 0x002 e jmp pcint2 ; pcint2 handler 0x003 0 jmp pcint3 ; pcint3 handler ; 0x003 2 reset : ldi r16, high(ramend) ; main program start 0x003 3 out sph,r16 ; set stack pointer to top of ram 0x003 4 ldi r16, low(ramend) 0x003 5 out spl,r16 0x003 6 sei ; enable interrupts 0x003 7 xxx ... ... ... 52 2570n?avr?05/11 atmega325/3250/645/6450 when the bootrst fuse is unprogrammed, the boot section size set to 4k bytes and the ivsel bit in the mcucr register is set before an y interrupts are enabled, the most typical and general program setup for the reset and interrupt vector addresses is: address labels code comments 0x0000 reset: ldi r16,high(ramend); main program start 0x0001 out sph,r16 ; set stack pointer to top of ram 0x0002 ldi r16,low(ramend) 0x0003 out spl,r16 0x0004 sei ; enable interrupts 0x0005 53 2570n?avr?05/11 atmega325/3250/645/6450 when the bootrst fuse is programmed, the boot section size set to 4k bytes and the ivsel bit in the mcucr register is set before any interr upts are enabled, the mo st typical and general program setup for the reset and interrupt vector addresses is: address labels code comments ; .org 0x3800/0x7800 0x3800/0x7800 jmp reset ; reset handler 0x3802/0x7802 jmp ext_int0 ; irq0 handler 0x3804/0x7804 jmp pcint0 ; pcint0 handler ... ... ... ; 0x382c/0x782c jmp spm_rdy ; store program memory ready handler ; 0x382e/0x782ereset:ldir16,high(ramend); main program start 0x382f/0x782f out sph,r16 ; set stack pointer to top of ram 0x3830/0x7830 ldi r16,low(ramend) 0x3831/0x7831 out spl,r16 0x3832/0x7832 sei ; enable interrupts 0x3833/0x7833 54 2570n?avr?05/11 atmega325/3250/645/6450 in the application section and boot lock bit blb12 is programed, interrupts are disabled while executing from the boot loader section. refer to the section ?boot loader support ? read-while- write self-programming? on page 251 for details on boot lock bits. ? bit 0 ? ivce: interrupt vector change enable the ivce bit must be written to logic one to enable change of the ivsel bit. ivce is cleared by hardware four cyc les after it is written or when ivsel is written. sett ing the ivce bit will disable interrupts, as explained in the ivsel description above. see code example below. assembly code example move_interrupts: ;get mcucr in r16, mcucr mov r17, r16 ; enable change of interrupt vectors ori r16, (1< 56 2570n?avr?05/11 atmega325/3250/645/6450 figure 13-1. pin change interrupt 13.2 register description 13.2.1 eicra ? external interrupt control register a the external interrupt control register a contains control bits for interrupt sense control. ? bit 1, 0 ? isc01, isc00: interrupt sense control 0 bit 1 and bit 0 the external interrupt 0 is activated by the exte rnal pin int0 if the sreg i-flag and the corre- sponding interrupt mask are set. the level and edges on the external int0 pin that activate the interrupt are defined in table 13-1 . the value on the int0 pin is sampled before detecting edges. if edge or toggle interrupt is selected, pulses that last longer than one clock period will generate an interrupt. shorter pulses are not guaranteed to generate an interrupt. if low level interrupt is selected, the low level must be held until the completion of the currently executing instruction to generate an interrupt. clk pcint(n) pin_lat pin_sync pcint_in_(n) pcint_syn pcint_setflag pcif pcint(0) pin_sync pcint_syn pin_lat d q le pcint_setflag pcif clk clk pcint(0) in pcmsk(x) pcint_in_(0) 0 x bit 76543210 (0x69) ? ? ? ? ? ? isc01 isc00 eicra read/writerrrrrrr/wr/w initial value00000000 table 13-1. interrupt 0 sense control isc01 isc00 description 0 0 the low level of int0 generates an interrupt request. 0 1 any logical change on int0 generates an interrupt request. 1 0 the falling edge of int0 generates an interrupt request. 1 1 the rising edge of int0 generates an interrupt request. 57 2570n?avr?05/11 atmega325/3250/645/6450 13.2.2 eimsk ? external interrupt mask register ? bit 7 ? pcie3: pin change interrupt enable 3 when the pcie3 bit is set (one) and the i-bit in the status register (sreg) is set (one), pin change interrupt 3 is enabled. any change on any enabled pcin t30..24 pin will cause an inter- rupt. the corresponding interrupt of pin change interrupt request is executed from the pcint3 interrupt vector. pcint30..24 pins are enabled individually by the pcmsk3 register. this bit is reserved bit in atmega325/645 and should always be written to zero. ? bit 6 ? pcie2: pin change interrupt enable 2 when the pcie2 bit is set (one) and the i-bit in the status register (sreg) is set (one), pin change interrupt 2 is enabled. any change on any enabled pcin t23..16 pin will cause an inter- rupt. the corresponding interrupt of pin change interrupt request is executed from the pcint2 interrupt vector. pcint23..16 pins are enabled individually by the pcmsk2 register. this bit is reserved bit in atmega325/645 and should always be written to zero. ? bit 5 ? pcie1: pin change interrupt enable 1 when the pcie1 bit is set (one) and the i-bit in the status register (sreg) is set (one), pin change interrupt 1 is enabled. any change on any enabled pcint15.. 8 pin will cause an inter- rupt. the corresponding interrupt of pin change interrupt request is executed from the pcint1 interrupt vector. pcint15.. 8 pins are enabled individually by the pcmsk1 register. ? bit 4 ? pcie0: pin change interrupt enable 0 when the pcie0 bit is set (one) and the i-bit in the status register (sreg) is set (one), pin change interrupt 0 is enabled. any change on any enabled pcint7..0 pin will cause an interrupt. the corresponding interrupt of pin change interrupt request is executed from the pcint0 inter- rupt vector. pcint7..0 pins are enabled individually by the pcmsk0 register. ? bit 0 ? int0: external interrupt request 0 enable when the int0 bit is set (one) and the i-bit in the status register (sreg) is set (one), the exter- nal pin interrupt is enabled. the interrupt sens e control0 bits 1/0 (isc01 and isc00) in the external interrupt control register a (eicra) define whether the external interrupt is activated on rising and/or falling edge of the int0 pin or le vel sensed. activity on the pin will cause an interrupt request even if int0 is configured as an output. the corresponding interrupt of external interrupt request 0 is executed from the int0 interrupt vector. 13.2.3 eifr ? external interrupt flag registe ? bit 7? pcif3: pin change interrupt flag 3 when a logic change on any pcint30..24 pin triggers an interrupt request, pcif3 becomes set (one). if the i-bit in sreg and the pcie3 bit in eimsk are set (one), the mcu will jump to the bit 76543210 0x1d (0x3d) pcie3 pcie2 pcie1 pcie0 ? ? ?int0eimsk read/write r/w r/w r/w r/w r r r r/w initial value 0 0 0 0 0 0 0 0 bit 76543210 0x1c (0x3c) pcif3 pcif2 pcif1 pcif0 ? ? ? intf0 eifr read/write r/w r/w r/w r/w r r r r/w initial value 0 0 0 0 0 0 0 0 58 2570n?avr?05/11 atmega325/3250/645/6450 corresponding interrupt vector. the flag is cleared when the interrupt routine is executed. alter- natively, the flag can be cleared by writing a logical one to it. this bit is reserved bit in atmega325/645 and will always be read as zero. ? bit 6? pcif2: pin change interrupt flag 2 when a logic change on any pcint24..16 pin triggers an interrupt request, pcif2 becomes set (one). if the i-bit in sreg and the pcie2 bit in eimsk are set (one), the mcu will jump to the corresponding interrupt vector. the flag is cleared when the interrupt routine is executed. alter- natively, the flag can be cleared by writing a logical one to it. this bit is reserved bit in atmega325/645 and will always be read as zero. ? bit 5? pcif1: pin change interrupt flag 1 when a logic change on any pcint15.. 8 pin triggers an interrupt request, pcif1 becomes set (one). if the i-bit in sreg and the pcie1 bit in eimsk are set (one), the mcu will jump to the corresponding interrupt vector. the flag is cleared when the interrupt routine is executed. alter- natively, the flag can be cleared by writing a logical one to it. ? bit 4? pcif0: pin change interrupt flag 0 when a logic change on any pcint7..0 pin triggers an interrupt request, pcif0 becomes set (one). if the i-bit in sreg and the pcie0 bit in eimsk are set (one), the mcu will jump to the corresponding interrupt vector. the flag is cleared when the interrupt routine is executed. alter- natively, the flag can be cleared by writing a logical one to it. ? bit 0 ? intf0: external interrupt flag 0 when an edge or logic change on the int0 pin triggers an interrupt request, intf0 becomes set (one). if the i-bit in sreg and the int0 bit in eimsk are set (o ne), the mcu will jump to the cor- responding interrupt vector. the flag is cleared when the interrupt routine is executed. alternatively, the flag can be cleared by writing a logical one to it. this flag is always cleared when int0 is configured as a level interrupt. 13.2.4 pcmsk3 ? pin change mask register 3 (1) ? bit 6:0 ? pcint30:24: pin change enable mask 30:24 each pcint30:24-bit selects whether pin change interrupt is enabled on the corresponding i/o pin. if pcint30:24 is set and the pcie3 bit in eimsk is set, pin change interrupt is enabled on the corresponding i/o pin. if pcint30:24 is cleared, pin change interrupt on the corresponding i/o pin is disabled. 13.2.5 pcmsk2 ? pin change mask register 2 (1) bit 76543210 (0x73) ? pcint30 pcint29 pcint28 pcint27 pcint26 pcint25 pcint24 pcmsk3 read/write r r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 bit 76543210 (0x6d) pcint23 pcint22 pcint21 pcint20 pcint19 pcint18 pcint17 pcint16 pcmsk2 read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value 00000000 59 2570n?avr?05/11 atmega325/3250/645/6450 ? bit 7:0 ? pcint23:16: pin change enable mask 23..16 each pcint23:16 bit selects whether pin change interrupt is enabled on the corresponding i/o pin. if pcint23:16 is set and the pcie2 bit in eimsk is set, pin change interrupt is enabled on the corresponding i/o pin. if pcint23:16 is cleared, pin change interrupt on the corresponding i/o pin is disabled. note: 1. pcmsk3 and pcmsk2 are only present in atmega3250/6450. 13.2.6 pcmsk1 ? pin change mask register 1 ? bit 7:0 ? pcint15:8: pin change enable mask 15..8 each pcint15: 8 -bit selects whether pin change interrupt is enabled on the corresponding i/o pin. if pcint15: 8 is set and the pcie1 bit in eimsk is set, pin change interrupt is enabled on the corresponding i/o pin. if pcint15: 8 is cleared, pin change interrupt on the corresponding i/o pin is disabled. 13.2.7 pcmsk0 ? pin change mask register 0 ? bit 7:0 ? pcint7:0: pin change enable mask 7..0 each pcint7:0 bit selects whether pin change interrupt is enabled on the corresponding i/o pin. if pcint7:0 is set and the pcie0 bit in eimsk is set, pin change interrupt is enabled on the cor- responding i/o pin. if pcint7:0 is cleared, pi n change interrupt on the corresponding i/o pin is disabled. bit 76543210 (0x6c) pcint15 pcint14 pcint13 pcint12 pcint11 pcint10 pcint9 pcint8 pcmsk1 read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 bit 76543210 (0x6b) pcint7 pcint6 pcint5 pcint4 pcint3 pcint2 pcint1 pcint0 pcmsk0 read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 60 2570n?avr?05/11 atmega325/3250/645/6450 14. i/o-ports 14.1 overview all avr ports have true read-modi fy-write functionality when used as general digital i/o ports. this means that the direction of one port pin can be changed without unintentionally changing the direction of any other pin with the sbi and cbi instructions. the same applies when chang- ing drive value (if configured as output) or enabling/disabling of pull-up resistors (if configured as input). each output buffer has symmetrical drive characteristics with both high sink and source capability. port b has a higher pi n driver strength than the other ports, but all the pin drivers are strong enough to drive led displays directly. all port pins have individually selectable pull-up resistors with a supply-voltage invariant resistanc e. all i/o pins have protection diodes to both v cc and ground as indicated in figure 14-1 . refer to ?electrical characteristics? on page 297 for a complete list of parameters. if exceeding the pin voltage ?absolute maximum ratings?, result- ing currents can harm the device if not limited accordingly. for segment pins used as general i/o, the same situation can also influence the lcd voltage level. figure 14-1. i/o pin equivalent schematic all registers and bit references in this section are written in general form. a lower case ?x? repre- sents the numbering letter for the port, and a lower case ?n? represents the bit number. however, when using the register or bit defines in a progr am, the precise form must be used. for example, portb3 for bit no. 3 in port b, here documented generally as portxn. the physical i/o regis- ters and bit locations are listed in ?register description? on page 8 1 . three i/o memory address locations are allocated for each port, one each for the data register ? portx, data direction register ? ddrx, and the port input pins ? pinx. the port input pins i/o location is read only, while the data register and the data direction register are read/write. however, writing a logic one to a bit in the pinx register, will result in a toggle in the correspond- ing bit in the data register. in addition, the pu ll-up disable ? pud bit in mcucr disables the pull-up function for all pins in all ports when set. using the i/o port as general digital i/o is described in ?ports as general digital i/o? on page 61 . most port pins are multiplexed with alternate functions for the peripheral features on the device. how each alternate function interferes with the port pin is described in ?alternate port c pin logic r pu see figure "general digital i/o" for details pxn 61 2570n?avr?05/11 atmega325/3250/645/6450 functions? on page 66 . refer to the individual module sectio ns for a full description of the alter- nate functions. note that enabling the alternate function of some of the port pins does not affect the use of the other pins in the port as general digital i/o. 14.2 ports as gener al digital i/o the ports are bi-directional i/o ports with optional internal pull-ups. figure 14-2 shows a func- tional description of one i/o-port pin, here generically called pxn. figure 14-2. general digital i/o (1) note: 1. wrx, wpx, wdx, rrx, rpx, and rdx are common to all pins within the same port. clk i/o , sleep, and pud are common to all ports. 14.2.1 configuring the pin each port pin consists of three register bits: ddxn, portxn, and pinxn. as shown in ?register description? on page 8 1 , the ddxn bits are accessed at the ddrx i/o address, the portxn bits at the portx i/o address, and the pinxn bits at the pinx i/o address. the ddxn bit in the ddrx register selects the direct ion of this pin. if ddxn is written logic one, pxn is configured as an output pin. if ddxn is written logic zero, pxn is configured as an input pin. if portxn is written logic one when the pin is c onfigured as an input pin, the pull-up resistor is activated. to switch the pull-up resistor off, portxn has to be written logic zero or the pin has to clk rpx rrx rdx wdx pud synchronizer wdx: write ddrx wrx: write portx rrx: read portx register rpx: read portx pin pud: pullup disable clk i/o : i/o clock rdx: read ddrx d l q q reset reset q q d q q d clr portxn q q d clr ddxn pinxn data b u s sleep sleep: sleep control pxn i/o wpx 0 1 wrx wpx: write pinx register 62 2570n?avr?05/11 atmega325/3250/645/6450 be configured as an output pin. the port pins are tri-stated when reset condition becomes active, even if no clocks are running. if portxn is written logic one when the pin is conf igured as an output pin, the port pin is driven high (one). if portxn is written logic zero when the pin is configured as an output pin, the port pin is driven low (zero). 14.2.2 toggling the pin writing a logic one to pinxn toggles the value of portxn, independent on the value of ddrxn. note that the sbi instruction can be used to toggle one single bit in a port. 14.2.3 switching between input and output when switching between tri-state ({ddxn, portxn} = 0b00) and output high ({ddxn, portxn} = 0b11), an intermediate state with either pull-up enabled {ddxn, portxn} = 0b01) or output low ({ddxn, portxn} = 0b10) must occur. norma lly, the pull-up enabled state is fully accept- able, as a high-impedant enviro nment will not notice the differenc e between a strong high driver and a pull-up. if this is not the case, the pud bit in the mcucr register can be set to disable all pull-ups in all ports. switching between input with pull-up and output low generates the same problem. the user must use either the tri-state ({ddxn, portxn} = 0b00) or the output high state ({ddxn, portxn} = 0b11) as an intermediate step. table 14-1 summarizes the control signals for the pin value. 14.2.4 reading the pin value independent of the setting of data direction bit ddxn, the port pin can be read through the pinxn register bit. as shown in figure 14-2 , the pinxn register bit and the preceding latch con- stitute a synchronizer. this is needed to avoid metastability if the physical pin changes value near the edge of the internal clock, but it also introduces a delay. figure 14-3 shows a timing dia- gram of the synchronization when reading an externally applied pin value. the maximum and minimum propagation delays are denoted t pd,max and t pd,min respectively. table 14-1. port pin configurations ddxn portxn pud (in mcucr) i/o pull-up comment 0 0 x input no tri-state (hi-z) 0 1 0 input yes pxn will source current if ext. pulled low. 0 1 1 input no tri-state (hi-z) 1 0 x output no output low (sink) 1 1 x output no output high (source) 63 2570n?avr?05/11 atmega325/3250/645/6450 figure 14-3. synchronization when reading an externally applied pin value xxx in r17, pinx 0x00 0xff instructions sync latch pinxn r17 xxx system clk t pd, max t pd, min 64 2570n?avr?05/11 atmega325/3250/645/6450 consider the clock period starting shortly after the first falling edge of the system cl ock. the latch is closed when the clock is low, and goes transpa rent when the clock is high, as indicated by the shaded region of the ?sync latch? signal. the signal value is latched when the system clock goes low. it is clocked into the pinxn register at the succeeding positive clock edge. as indi- cated by the two arrows tpd,max and tpd,min, a single signal tr ansition on the pin will be delayed between ? and 1? system clock period depending upon the time of assertion. when reading back a software assigned pin value, a nop instruction must be inserted as indi- cated in figure 14-4 . the out instruction sets the ?sync latch? signal at the positive edge of the clock. in this case, the delay tpd through the synchronizer is 1 system clock period. figure 14-4. synchronization when reading a software assigned pin value the following code example shows how to set port b pins 0 and 1 high, 2 and 3 low, and define the port pins from 4 to 7 as input with pull-ups assigned to port pins 6 and 7. the resulting pin values are read back again, but as previously di scussed, a nop instruction is included to be able to read back the value recently assigned to some of the pins. out portx, r16 nop in r17, pinx 0xff 0x00 0xff system clk r16 instructions sync latch pinxn r17 t pd 65 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. for the assembly program, two temporary registers are used to minimize the time from pull- ups are set on pins 0, 1, 6, and 7, until the direction bits are correctly set, defining bit 2 and 3 as low and redefining bits 0 and 1 as strong high drivers. 14.2.5 digital input enable and sleep modes as shown in figure 14-2 , the digital input signal can be clamped to ground at the input of the schmitt-trigger. the sig nal denoted sleep in the figure, is set by the mcu sleep controller in power-down mode, power-save mode, and standby mode to avoid high power consumption if some input signals are left floating, or have an analog signal level close to v cc /2. sleep is overridden for port pins enabled as ex ternal interrupt pins. if the external interrupt request is not e nabled, sleep is active also for these pins. sl eep is also overri dden by various other alternate functions as described in ?alternate port functions? on page 66 . if a logic high level (?one?) is present on an asynchronous external interrupt pin configured as ?interrupt on rising edge, falling edge, or any logic change on pin? while the external interrupt is not enabled, the corresponding external interrupt flag will be set when resuming from the above mentioned sleep mode, as the clamping in these sleep mode produces the requested logic change. 14.2.6 unconnected pins if some pins are unused, it is recommended to ens ure that these pins have a defined level. even though most of the digital inputs are disabled in the deep sleep modes as described above, float- assembly code example (1) ... ; define pull-ups and set outputs high ; define directions for port pins ldi r16,(1< 67 2570n?avr?05/11 atmega325/3250/645/6450 table 14-2 summarizes the function of the overriding signals. the pin and port indexes from fig- ure 14-5 are not shown in the succeeding tables. the overriding signals are generated internally in the modules having the alternate function. the following subsections shortly describe the alternate functions for each port, and relate the overriding signals to the alternate function. refer to the alternate function description for further details. table 14-2. generic description of overriding signals for alternate functions signal name full name description puoe pull-up override enable if this signal is set, the pull-up enable is controlled by the puov signal. if this signal is cleared, the pull-up is enabled when {ddxn, portxn, pud} = 0b010. puov pull-up override value if puoe is set, the pull-up is enabled/disabled when puov is set/cleared, regardless of the setting of the ddxn, portxn, and pud register bits. ddoe data direction override enable if this signal is set, the output driver enable is controlled by the ddov signal. if this signal is cleared, the output driver is enabled by the ddxn register bit. ddov data direction override value if ddoe is set, the output driver is enabled/disabled when ddov is set/cleared, regardless of the setting of the ddxn register bit. pvoe port value override enable if this signal is set and the output driver is enabled, the port value is controlled by the pvov signal. if pvoe is cleared, and the output driver is enabled, the port value is controlled by the portxn register bit. pvov port value override value if pvoe is set, the port value is set to pvov, regardless of the setting of the portxn register bit. ptoe port toggle override enable if ptoe is set, the portxn register bit is inverted. dieoe digital input enable override enable if this bit is set, the digital input enable is controlled by the dieov signal. if this signal is cleared, the digital input enable is determined by mcu state (normal mode, sleep mode). dieov digital input enable override value if dieoe is set, the digital input is enabled/disabled when dieov is set/cleared, regardless of the mcu state (normal mode, sleep mode). di digital input this is the digital input to alternate functions. in the figure, the signal is connected to the output of the schmitt trigger but before the synchronizer. unless the digital input is used as a clock source, the module with the alternate function will use its own synchronizer. aio analog input/output this is the analog input/output to/from alternate functions. the signal is connected directly to the pad, and can be used bi-directionally. 68 2570n?avr?05/11 atmega325/3250/645/6450 14.3.1 alternate functions of port b the port b pins with alternate functions are shown in table 14-3 . the alternate pin configuration is as follows: ? oc2a/pcint15, bit 7 oc2, output compare match a output: the pb7 pin can serve as an external output for the timer/counter2 output compare a. the pin has to be configured as an output (ddb7 set (one)) to serve this function. the oc2a pin is also the output pin for the pwm mode timer function. pcint15, pin change interrupt source 15: the pb7 pin can serve as an external interrupt source. ? oc1b/pcint14, bit 6 oc1b, output compare match b output: the pb6 pin can serve as an external output for the timer/counter1 output compare b. the pin has to be configured as an output (ddb6 set (one)) to serve this function. the oc1b pin is also the output pin for the pwm mode timer function. pcint14, pin change interrupt source 14: the pb6 pin can serve as an external interrupt source. table 14-3. port b pins alternate functions port pin alternate functions pb7 oc2a/pcint15 (output compare and pwm output a for timer/counter2 or pin change interrupt15). pb6 oc1b/pcint 14 (output compare and pwm output b for timer/counter1 or pin change interrupt14). pb5 oc1a/pcint13 (output compare and pwm output a for timer/counter1 or pin change interrupt13). pb4 oc0a/pcint12 (output compare and pwm output a for timer/counter0 or pin change interrupt12). pb3 miso/pcint11 (spi bus master input/slave output or pin change interrupt11). pb2 mosi/pcint10 (spi bus master output/slave input or pin change interrupt10). pb1 sck/pcint9 (spi bus serial clock or pin change interrupt9). pb0 ss/pcint 8 (spi slave select input or pin change interrupt 8 ). 69 2570n?avr?05/11 atmega325/3250/645/6450 ? oc1a/pcint13, bit 5 oc1a, output compare match a output: the pb5 pin can serve as an external output for the timer/counter1 output compare a. the pin has to be configured as an output (ddb5 set (one)) to serve this function. the oc1a pin is also the output pin for the pwm mode timer function. pcint13, pin change interrupt source 13: the pb5 pin can serve as an external interrupt source. ? oc0a/pcint12, bit 4 oc0a, output compare match a output: the pb4 pin can serve as an external output for the timer/counter0 output compare a. the pin has to be configured as an output (ddb4 set (one)) to serve this function. the oc0a pin is also the output pin for the pwm mode timer function. pcint12, pin change interrupt source 12: the pb4 pin can serve as an external interrupt source. ? miso/pcint11 ? port b, bit 3 miso: master data input, slave data output pin for spi. when the spi is enabled as a master, this pin is configured as an input regardless of the setting of ddb3. when the spi is enabled as a slave, the data direction of this pin is cont rolled by ddb3. when the pin is forced to be an input, the pull-up can still be controlled by the portb3 bit. pcint11, pin change interrupt source 11: the pb3 pin can serve as an external interrupt source. ? mosi/pcint10 ? port b, bit 2 mosi: spi master data output, slave data input for spi. when the spi is enabled as a slave, this pin is configured as an input regardless of the setting of ddb2. when the spi is enabled as a master, the data direction of this pin is controlled by ddb2. when the pin is forced to be an input, the pull-up can still be controlled by the portb2 bit. pcint10, pin change interrupt source 10: the pb2 pin can serve as an external interrupt source. ? sck/pcint9 ? port b, bit 1 sck: master clock output, slave clock input pin for spi. when the spi is enabled as a slave, this pin is configured as an input regardless of the setting of ddb1. when the spi is enabled as a master, the data direction of this pin is controlled by ddb1. when the pin is forced to be an input, the pull-up can still be controlled by the portb1 bit. pcint9, pin change interrupt source 9: the pb1 pin can serve as an external interrupt source. ?ss /pcint8 ? port b, bit 0 ss : slave port select input. when the spi is enabled as a slave, this pin is configured as an input regardless of the setting of ddb0. as a slave, the spi is activated when this pin is driven low. when the spi is enabled as a master, the data di rection of this pin is controlled by ddb0. when the pin is forced to be an input, the pull-up can still be controlled by the portb0 bit pcint 8 , pin change interrupt source 8 : the pb0 pin can serve as an external interrupt source. 70 2570n?avr?05/11 atmega325/3250/645/6450 table 14-4 and table 14-5 relate the alternate functions of port b to the overriding signals shown in figure 14-5 on page 66 . spi mstr input and spi sl ave output constitute the miso signal, while mosi is divided in to spi mstr output and spi slave input. table 14-4. overriding signals for alternate functions in pb7:pb4 signal name pb7/oc2a/ pcint15 pb6/oc1b/ pcint14 pb5/oc1a/ pcint13 pb4/oc0a/ pcint12 puoe0000 puov0000 ddoe 0 0 0 0 ddov 0 0 0 0 pvoe oc2a enable oc1b enable oc1a enable oc0a enable pvov oc2a oc1b oc1a oc0a ptoe???? dieoe pcint15 ? pcie1 pcint14 ? pcie1 pcint13 ? pcie1 pcint12 ? pcie1 dieov1111 di pcint15 input pcint14 input pcint13 input pcint12 input aio???? table 14-5. overriding signals for alternate functions in pb3:pb0 signal name pb3/miso/ pcint11 pb2/mosi/ pcint10 pb1/sck/ pcint9 pb0/ss / pcint8 puoe spe ? mstr spe ? mstr spe ? mstr spe ? mstr puov portb3 ? pud portb2 ? pud portb1 ? pud portb0 ? pud ddoe spe ? mstr spe ? mstr spe ? mstr spe ? mstr ddov 0 0 0 0 pvoe spe ? mstr spe ? mstr spe ? mstr 0 pvov spi slave output spi mstr output sck output 0 ptoe???? dieoe pcint11 ? pcie1 pcint10 ? pcie1 pcint9 ? pcie1 pcint 8 ? pcie1 dieov1111 di pcint11 input spi mstr input pcint10 input spi slave input pcint9 input sck input pcint 8 input spi ss aio???? 71 2570n?avr?05/11 atmega325/3250/645/6450 14.3.2 alternate functions of port d the port d pins with alternate functions are shown in table 14-6 . the alternate pin configuration is as follows: ?int0 ? port d, bit 1 int0, external interrupt source 0. the pd1 pin can serve as an external interrupt source to the mcu. ? icp1 ? port d, bit 0 icp1 ? input capture pin1: the pd0 pin can act as an input capture pin for timer/counter1. table 14-7 relates the alternate functions of port d to the overriding signals shown in figure 14- 5 on page 66 . table 14-6. port d pins alternate functions port pin alternate function pd7 - pd6 - pd5 - pd4 - pd3 - pd2 - pd1 int0 (external interrupt0 input) pd0 icp1 (timer/counter1 input capture pin) table 14-7. overriding signals for alte rnate functions in pd3:pd0 signal name pd3 pd2 pd1/int0 pd0/icp1 puoe0000 puov0000 ddoe 0 0 0 0 ddov 0 0 0 0 pvoe0000 pvov0000 ptoe???? dieoe 0 0 int0 enable 0 dieov 0 0 int0 enable 0 di ? ? int0 input icp1 input aio???? 72 2570n?avr?05/11 atmega325/3250/645/6450 14.3.3 alternate functions of port e the port e pins with alternate functions are shown in table 14- 8 . ? pcint7 ? port e, bit 7 pcint7, pin change interrupt source 7: the pe7 pin can serve as an external interrupt source. clko, divided system clock: the divided syst em clock can be output on the pe7 pin. the divided system clock will be output if the ck out fuse is programmed, regardless of the porte7 and dde7 settings. it will also be output during reset. ? do/pcint6 ? port e, bit 6 do, universal serial interface data output. pcint6, pin change interrupt source 6: the pe6 pin can serve as an external interrupt source. ? di/sda/pcint5 ? port e, bit 5 di, universal serial interface data input. sda, two-wire serial interface data: pcint5, pin change interrupt source 5: the pe5 pin can serve as an external interrupt source. ? usck/scl/pcint4 ? port e, bit 4 usck, universal serial interface clock. scl, two-wire serial interface clock. pcint4, pin change interrupt source 4: the pe4 pin can serve as an external interrupt source. ? ain1/pcint3 ? port e, bit 3 ain1 ? analog comparator negative input. this pi n is directly connected to the negative input of the analog comparator. pcint3, pin change interrupt source 3: the pe3 pin can serve as an external interrupt source. table 14-8. port e pins alternate functions port pin alternate function pe7 pcint7 (pin change interrupt7) clko (divided system clock) pe6 do/pcint6 (usi data output or pin change interrupt6) pe5 di/sda/pcint5 (usi data input or twi serial data or pin change interrupt5) pe4 usck/scl/pcint4 (usart external clock input/output or twi serial clock or pin change interrupt4) pe3 ain1/pcint3 (analog comparator negative input or pin change interrupt3) pe2 xck/ain0/ pcint2 (usart external cl ock or analog comparator positive input or pin change interrupt2) pe1 txd/pcint1 (usart transmit pin or pin change interrupt1) pe0 rxd/pcint0 (usart receive pin or pin change interrupt0) 73 2570n?avr?05/11 atmega325/3250/645/6450 ? xck/ain0/pcint2 ? port e, bit 2 xck, usart external clock. the data direction re gister (dde2) controls whether the clock is output (dde2 set) or input (dde2 cleared). t he xck pin is active only when the usart oper- ates in synchronous mode. ain0 ? analog comparator positive input. this pin is directly connected to the positive input of the analog comparator. pcint2, pin change interrupt source 2: the pe2 pin can serve as an external interrupt source. ? txd/pcint1 ? port e, bit 1 txd0, uart0 transmit pin. pcint1, pin change interrupt source 1: the pe1 pin can serve as an external interrupt source. ? rxd/pcint0 ? port e, bit 0 rxd, usart receive pin. receive data (dat a input pin for the usart). when the usart receiver is enabled this pin is configured as an input regardless of the value of dde0. when the usart forces this pin to be an input, a logical one in porte0 will turn on the internal pull-up. pcint0, pin change interrupt source 0: the pe0 pin can serve as an external interrupt source. table 14-9 and table 14-10 relates the alternate functions of port e to the overriding signals shown in figure 14-5 on page 66 . note: 1. ckout is one if the ckout fuse is programmed table 14-9. overriding signals for alternate functions pe7:pe4 signal name pe7/pcint7 pe6/do/ pcint6 pe5/di/sda/ pcint5 pe4/usck/scl/ pcint4 puoe 0 0 usi_two-wire usi_two-wire puov0000 ddoe ckout (1) 0 usi_two-wire usi_two-wire ddov 1 0 (sda + porte5 ) ? dde5 (usi_scl_hol d + porte4 ) ? dde4 pvoe ckout (1) usi_three- wire usi_two-wire ? dde5 usi_two-wire ? dde4 pvov clk i/o do 0 0 ptoe ? ? 0 usitc dieoe pcint7 ? pcie0 pcint6 ? pcie0 (pcint5 ? pcie0) + usisie (pcint4 ? pcie0) + usisie dieov1111 di pcint7 input pcint6 input di/sda input pcint5 input usckl/scl input pcint4 input aio???? 74 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. ain0d and ain1d is described in ?didr1 ? digital input disable register 1? on page 200 . 14.3.4 alternate functions of port f the port f has an alternate function as analog input for the adc as shown in table 14-11 . if some port f pins are configured as outputs, it is essential that these do not switch when a con- version is in progress. this might corrupt the re sult of the conversion. if the jtag interface is enabled, the pull-up re sistors on pins pf7(tdi), pf5(tms) and pf4(tck) will be activated even if a reset occurs. ? tdi, adc7 ? port f, bit 7 adc7, analog to digital converter, channel 7 . tdi, jtag test data in: serial input data to be shifted in to the instruction register or data reg- ister (scan chains). when the jtag interface is enabled, this pin can not be used as an i/o pin. table 14-10. overriding signals for alternate functions in pe3:pe0 signal name pe3/ain1/ pcint3 pe2/xck/ain0/ pcint2 pe1/txd/ pcint1 pe0/rxd/pcint 0 puoe 0 xck output enable txen rxen puov 0 xck 0 porte0 ? pud ddoe 0 0 txen rxen ddov 0 0 1 0 pvoe 0 0 txen 0 pvov 0 0 txd 0 ptoe???? dieoe (pcint3 ? pcie0) + ain1d (1) (pcint2 ? pcie0) + ain0d (1) pcint1 ? pcie0 pcint0 ? pcie0 dieov pcint3 ? pcie0 pcint2 ? pcie0 1 1 di pcint3 input xck/pcint2 input pcint1 inpu t rxd/pcint0 input aio ain1 input ain0 input ? ? table 14-11. port f pins alternate functions port pin alternate function pf7 adc7/tdi (adc input channel 7 or jtag test data input) pf6 adc6/tdo (adc input channel 6 or jtag test data output) pf5 adc5/tms (adc input channel 5 or jtag test mode select) pf4 adc4/tck (adc input channel 4 or jtag test clock) pf3 adc3 (adc input channel 3) pf2 adc2 (adc input channel 2) pf1 adc1 (adc input channel 1) pf0 adc0 (adc input channel 0) 75 2570n?avr?05/11 atmega325/3250/645/6450 ? tdo, adc6 ? port f, bit 6 adc6, analog to digital converter, channel 6 . tdo, jtag test data out: serial output data from instruction register or data register. when the jtag interface is enabled, this pin can not be used as an i/o pin. in tap states that shift out data, the tdo pin drives actively. in other states the pin is pulled high. ? tms, adc5 ? port f, bit 5 adc5, analog to digital converter, channel 5 . tms, jtag test mode select: this pin is used fo r navigating through the tap-controller state machine. when the jtag interface is enabled, this pin can not be used as an i/o pin. ? tck, adc4 ? port f, bit 4 adc4, analog to digital converter, channel 4 . tck, jtag test clock: jtag operation is synch ronous to tck. when the jtag interface is enabled, this pin can not be used as an i/o pin. ? adc3 - adc0 ? port f, bit 3:0 analog to digital converter, channel 3-0. table 14-12. overriding signals for alternate functions in pf7:pf4 signal name pf7/adc7/tdi pf6/adc6/t do pf5/adc5/tms pf4/adc4/tck puoe jtagen jtagen jtagen jtagen puov1111 d d o e j tag e n j tag e n j tag e n j tag e n ddov 0 shift_ir + shift_dr 00 pvoe 0 jtagen 0 0 pvov 0 tdo 0 0 ptoe???? d i e o e j tag e n j tag e n j tag e n j tag e n dieov0000 di???? aio tdi adc7 input adc6 input tms adc5 input tck adc4 input 76 2570n?avr?05/11 atmega325/3250/645/6450 14.3.5 alternate functions of port g the alternate pin configuration is as follows: note: 1. port g, pg5 is input only. pull-up is always on. see table 27-3 on page 266 for rstdisbl fuse. the alternate pin configuration is as follows: ? reset ? port g, bit 5 reset : external reset input. when the rstdisbl fuse is prog rammed ('0'), pg5 will function as input with pu ll-up always on. ? t0 ? port g, bit 4 t0, timer/counter0 counter source. ? t1 ? port g, bit 3 t1, timer/counter1 counter source. table 14-14 and table 14-15 relates the alternate functions of port g to the overriding signals shown in figure 14-5 on page 66 . table 14-13. overriding signals for alternate functions in pf3:pf0 signal name pf3/adc3 pf2/adc2 pf1/adc1 pf0/adc0 puoe0000 puov0000 ddoe 0 0 0 0 ddov 0 0 0 0 pvoe0000 pvov0000 ptoe???? dieoe0000 dieov0000 di???? aio adc3 input adc2 input adc1 input adc0 input table 14-14. port g pins alternate functions port pin alternate function pg5 reset (1) pg4 t0 (timer/counter0 clock inpu) pg3 t1 (timer/counter1 clock input) pg2 - pg1 - pg0 - 77 2570n?avr?05/11 atmega325/3250/645/6450 14.3.6 alternate functions of port h port h is only present in atmega3250/6450. the alternate pin configuration is as follows: the alternate pin configuration is as follows: ? pcint23 ? port h, bit 7 pcint23, pin change interrupt source 23: the ph7 pin can serve as an external interrupt source. ? pcint22 ? port h, bit 6 pcint22, pin change interrupt source 22: the ph6 pin can serve as an external interrupt source. ? pcint21 ? port h, bit 5 pcint21, pin change interrupt source 21: the ph5 pin can serve as an external interrupt source. table 14-15. overriding signals for alternate functions in pg4 and pg3 signal name pg4/t0 pg3/t1 puoe 0 0 puov 0 0 ddoe 0 0 ddov 0 0 pvoe 0 0 pvov 0 0 ptoe ? ? dieoe 0 0 dieov 0 0 di t0 input t1 input aio - - table 14-16. port h pins alternate functions port pin alternate function ph7 pcint23 (pin change interrupt23) ph6 pcint22 (pin change interrupt22) ph5 pcint21 (pin change interrupt21) ph4 pcint20 (pin change interrupt20) ph3 pcint19 (pin change interrupt19) ph2 pcint1 8 (pin change interrupt1 8 ) ph1 pcint17 (pin change interrupt17) ph0 pcint16 (pin change interrupt16) 78 2570n?avr?05/11 atmega325/3250/645/6450 ? pcint20 ? port h, bit 4 pcint20, pin change interrupt source 20: the ph4 pin can serve as an external interrupt source. ? pcint19 ? port h, bit 3 pcint19, pin change interrupt source 19: the ph3 pin can serve as an external interrupt source. ? pcint18 ? port h, bit 2 pcint1 8 , pin change interrupt source 1 8 : the ph2 pin can serve as an external interrupt source. ? pcint17 ? port h, bit 1 pcint17, pin change interrupt source 17: the p1 pin can serve as an external interrupt source. ? pcint16 ? port h, bit 0 pcint16, pin change interrupt source 16: the ph0 pin can serve as an external interrupt source. table 14-17 and table 14-1 8 relates the alternate functions of port h to the overriding signals shown in figure 14-5 on page 66 . table 14-17. overriding signals for alternate functions in ph7:4 signal name ph7/pcint23 ph6/pcint22 ph5/pcint21 ph4/pcint20 puoe0000 puov0000 ddoe 0 0 0 0 ddov 0 0 0 0 pvoe0000 pvov0000 ptoe???? dieoe pcint23 ? pcie0 pcint22 ? pcie0 pcint21 ? pcie0 pcint20 ? pcie0 dieov0000 di pcint23 input pcint22 input pcint21 input pcint20 input aio???? 79 2570n?avr?05/11 atmega325/3250/645/6450 14.3.7 alternate functions of port j port j is only present in atmega3250/6450. the alternate pin configuration is as follows: the alternate pin configuration is as follows: ? pcint30 ? port j, bit 6 pcint30, pin change interrupt source 30: the pe30 pin can serve as an external interrupt source. ? pcint29 ? port j, bit 5 pcint29, pin change interrupt source 29: the pe29 pin can serve as an external interrupt source. ? pcint28 ? port j, bit 4 pcint2 8 , pin change interrupt source 2 8 : the pe2 8 pin can serve as an external interrupt source. table 14-18. overriding signals for alternate functions in ph3:0 signal name ph3/pcint19 ph2/pcint18 ph1/pcint17 ph0/pcint16 puoe0000 puov0000 ddoe 0 0 0 0 ddov 0 0 0 0 pvoe0000 pvov0000 ptoe???? dieoe pcint19 ? pcie0 pcint1 8 ? pcie0 pcint17 ? pcie0 pcint16 ? pcie0 dieov0000 di pcint19 input pcint1 8 input pcint17 input pcint16 input aio???? table 14-19. port j pins alternate functions port pin alternate function pj6 pcint30 (pin change interrupt30) pj5 pcint29 (pin change interrupt29) pj4 pcint2 8 (pin change interrupt2 8 ) pj3 pcint27 (pin change interrupt27) pj2 pcint26(pin change interrupt26) pj1 pcint25(pin change interrupt25) pj0 pcint24 (pin change interrupt26) 80 2570n?avr?05/11 atmega325/3250/645/6450 ? pcint27 ? port j, bit 3 pcint27, pin change interrupt source 27: the pe27 pin can serve as an external interrupt source. ? pcint26 ? port j, bit 2 pcint26, pin change interrupt source 26: the pe26 pin can serve as an external interrupt source. ? pcint25 ? port j, bit 1 pcint25, pin change interrupt source 25: the pe25 pin can serve as an external interrupt source. ? pcint24 ? port j, bit 0 pcint24, pin change interrupt source 24: the pe24 pin can serve as an external interrupt source. table 14-20 and table 14-21 relates the alternate functions of port j to the overriding signals shown in figure 14-5 on page 66 . table 14-20. overriding signals for alternate functions in pj7:4 signal name pj6/pcint30 pj5/p cint29 pj4/pcint28 puoe 0 0 0 puov 0 0 0 ddoe 0 0 0 ddov 0 0 0 pvoe 0 0 0 pvov 0 0 0 ptoe ? ? ? dieoe pcint30 ? pcie0 pcint29 ? pcie0 pcint2 8 ? pcie0 dieov 0 0 0 di ? ? ? aio ? ? ? 81 2570n?avr?05/11 atmega325/3250/645/6450 14.4 register description 14.4.1 mcucr ? mcu control register ? bit 4 ? pud: pull-up disable when this bit is written to one, the pull-ups in the i/o ports are disabled even if the ddxn and portxn registers are configured to enable the pull-ups ({ddxn, portxn} = 0b01). see ?con- figuring the pin? on page 61 for more details about this feature. 14.4.2 porta ? port a data register 14.4.3 ddra ? port a data direction register 14.4.4 pina ? port a input pins address table 14-21. overriding signals for alternate functions in ph3:0 signal name pj3/pcint27 pj2/pcint2 6 pj1/pcint25 pj0/pcint24 puoe0000 puov0000 ddoe 0 0 0 0 ddov 0 0 0 0 pvoe0000 pvov0000 ptoe???? dieoe pcint27 ? pcie0 pcint26 ? pcie0 pcint25 ? pcie0 pcint24 ? pcie0 dieov0000 di???? aio???? bit 7 6 5 4 3 2 1 0 0x35 (0x55) jtd ? ?pud ? ? ivsel ivce mcucr read/write r/w r r r/w r r r/w r/w initial value 0 0 0 0 0 0 0 0 bit 76543210 0x02 (0x22) porta7 porta6 porta5 porta4 porta3 porta2 porta1 porta0 porta read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 0x01 (0x21) dda7 dda6 dda5 dda4 dda3 dda2 dda1 dda0 ddra read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 0x00 (0x20) pina7 pina6 pina5 pina4 pi na3 pina2 pina1 pina0 pina read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value n/a n/a n/a n/a n/a n/a n/a n/a 82 2570n?avr?05/11 atmega325/3250/645/6450 14.4.5 portb ? port b data register 14.4.6 ddrb ? port b data direction register 14.4.7 pinb ? port b input pins address 14.4.8 portc ? port c data register 14.4.9 ddrc ? port c data direction register 14.4.10 pinc ? port c input pins address 14.4.11 portd ? port d data register 14.4.12 ddrd ? port d data direction register bit 76543210 0x05 (0x25) portb7 portb6 portb5 portb4 portb3 portb2 portb1 portb0 portb read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 0x04 (0x24) ddb7 ddb6 ddb5 ddb4 ddb3 ddb2 ddb1 ddb0 ddrb read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 0x03 (0x23) pinb7 pinb6 pinb5 pinb4 pi nb3 pinb2 pinb1 pinb0 pinb read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value n/a n/a n/a n/a n/a n/a n/a n/a bit 76543210 0x0 8 (0x2 8 ) portc7 portc6 portc5 portc4 portc3 portc2 portc1 portc0 portc read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 0x07 (0x27) ddc7 ddc6 ddc5 ddc4 ddc3 ddc2 ddc1 ddc0 ddrc read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 0x06 (0x26) pinc7 pinc6 pinc5 pinc4 pi nc3 pinc2 pinc1 pinc0 pinc read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value n/a n/a n/a n/a n/a n/a n/a n/a bit 76543210 0x0b (0x2b) portd7 portd6 portd5 portd4 portd3 portd2 portd1 portd0 portd read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 0x0a (0x2a) ddd7 ddd6 ddd5 ddd4 ddd3 ddd2 ddd1 ddd0 ddrd read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 83 2570n?avr?05/11 atmega325/3250/645/6450 14.4.13 pind ? port d input pins address 14.4.14 porte ? port e data register 14.4.15 ddre ? port e data direction register 14.4.16 pine ? port e input pins address 14.4.17 portf ? port f data register 14.4.18 ddrf ? port f data direction register 14.4.19 pinf ? port f input pins address 14.4.20 portg ? port g data register bit 76543210 0x09 (0x29) pind7 pind6 pind5 pind4 pi nd3 pind2 pind1 pind0 pind read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value n/a n/a n/a n/a n/a n/a n/a n/a bit 76543210 0x0e (0x2e) porte7 porte6 porte5 porte4 porte3 porte2 porte1 porte0 porte read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 0x0d (0x2d) dde7 dde6 dde5 dde4 dde3 dde2 dde1 dde0 ddre read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 0x0c (0x2c) pine7 pine6 pine5 pine4 pine3 pine2 pine1 pine0 pine read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value n/a n/a n/a n/a n/a n/a n/a n/a bit 76543210 0x11 (0x31) portf7 portf6 portf5 portf4 portf3 portf2 portf1 portf0 portf read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 0x10 (0x30) ddf7 ddf6 ddf5 ddf4 ddf3 ddf2 ddf1 ddf0 ddrf read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 0x0f (0x2f) pinf7 pinf6 pinf5 pinf4 pinf3 pinf2 pinf1 pinf0 pinf read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value n/a n/a n/a n/a n/a n/a n/a n/a bit 76543210 0x14 (0x34) ??? portg4 portg3 portg2 portg1 portg0 portg read/write r r r r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 84 2570n?avr?05/11 atmega325/3250/645/6450 14.4.21 ddrg ? port g data direction register 14.4.22 ping ? port g input pins address 14.4.23 porth ? port h data register (1) 14.4.24 ddrh ? port h data direction register (1) 14.4.25 pinh ? port h input pins address (1) 14.4.26 portj ? port j data register (1) 14.4.27 ddrj ? port j data direction register (1) 14.4.28 pinj ? port j input pins address (1) note: 1. register only available in atmega3250/6450. bit 76543210 0x13 (0x33) ? ? ? ddg4 ddg3 ddg2 ddg1 ddg0 ddrg read/write r r r r/w r/w r/w r/w r/w initial value00000000 bit 76543210 0x12 (0x32) ? ? ping5 ping4 ping3 ping2 ping1 ping0 ping read/write r r r r/w r/w r/w r/w r/w initial value 0 0 0 n/a n/a n/a n/a n/a bit 7 6543210 (0xda) porth7 porth6 porth5 porth4 porth3 porth2 porth1 porth0 porth read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 bit 76543210 (0xd9) ddh7 ddh6 ddh5 ddh4 ddh3 ddh2 ddh1 ddh0 ddrh read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 (0xd 8 ) pinh7 pinh6 pinh5 pinh4 pi nh3 pinh2 pinh1 pinh0 pinh read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value n/a n/a n/a n/a n/a n/a n/a n/a bit 76543210 (0xdd) ? portj6 portj5 portj4 portj3 portj2 portj1 portj0 portj read/write r r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 bit 76543210 (0xdc) ? ddj6 ddj5 ddj4 ddj3 ddj2 ddj1 ddj0 ddrj read/write r r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 (0xdb) ? pinj6 pinj5 pinj4 pinj3 pinj2 pinj1 pinj0 pinj read/write r r/w r/w r/w r/w r/w r/w r/w initial value 0 n/a n/a n/a n/a n/a n/a n/a 85 2570n?avr?05/11 atmega325/3250/645/6450 15. 8-bit timer/counter0 with pwm 15.1 features timer/counter0 is a general purpose, single compare unit, 8 -bit timer/counter module. the main features are: ? single compare unit counter ? clear timer on compare match (auto reload) ? glitch-free, phase correct pu lse width modulator (pwm) ? frequency generator ? external event counter ? 10-bit clock prescaler ? overflow and compare match inte rrupt sources (tov0 and ocf0a) 15.2 overview a simplified block diagram of the 8 -bit timer/counter is shown in figure 15-1 . for the actual placement of i/o pins, refer to ?pinout atmega3250/6450? on page 2 and ?pinout atmega325/645? on page 3 . cpu accessible i/o registers, in cluding i/o bits and i/o pins, are shown in bold. the device-specific i/o register and bit locations are listed in the ?register description? on page 96 . figure 15-1. 8 -bit timer/counter block diagram 15.2.1 definitions many register and bit references in this section are written in general form. a lower case ?n? replaces the timer/counter number, in this case 0. a lower case ?x? replaces the output com- pare unit number, in this case unit a. however, when using the register or bit defines in a program, the precise form must be used, i.e., tcnt0 for accessing timer/counter0 counter value and so on. timer/counter data b u s = tcntn waveform generation ocn = 0 control logic = 0xff bottom count clear direction tovn (int.req.) ocrn tccrn clock select tn edge detector ( from prescaler ) clk tn top ocn (int.req.) 86 2570n?avr?05/11 atmega325/3250/645/6450 the definitions in table 15-1 are also used extensively throughout the document. 15.2.2 registers the timer/counter (tcnt0) and output compare register (ocr0a) are 8 -bit registers. inter- rupt request (abbreviated to int.req. in the figure) signals are all visible in the timer interrupt flag register (tifr0). all interrupts are individually masked with the timer interrupt mask reg- ister (timsk0). tifr0 and timsk0 are not shown in the figure. the timer/counter can be clocked internally, via the prescaler, or by an external clock source on the t0 pin. the clock select logic block controls which clock source and edge the timer/counter uses to increment (or decrement) its value. the timer/counter is inactive when no clock source is selected. the output from the clock select logic is referred to as the timer clock (clk t0 ). the double buffered output compare register (ocr0a) is compared with the timer/counter value at all times. the result of the compare can be used by the waveform generator to gener- ate a pwm or variable frequency output on the output compare pin (oc0a). see ?output compare unit? on page 8 7. for details. the compare match ev ent will also set the compare flag (ocf0a) which can be used to generate an output compare interrupt request. 15.3 timer/counter clock sources the timer/counter can be clocked by an internal or an external clock source. the clock source is selected by the clock select logic which is controlled by the clock select (cs02:0) bits located in the timer/counter control register (tccr0a). for details on clock sources and pres- caler, see ?timer/counter0 and timer/counter1 prescalers? on page 99 . table 15-1. definitions of timer/counter values. bottom the counter reaches the bottom when it becomes 0x00. max the counter reaches its maximum when it becomes 0xff (decimal 255). top the counter reaches the top when it becomes equal to the highest value in the count sequence. the top value can be assigned to be the fixed value 0xff (max) or the value stored in the ocr0a register. the assignment is dependent on the mode of operation. 87 2570n?avr?05/11 atmega325/3250/645/6450 15.4 counter unit the main part of the 8 -bit timer/counter is the programmable bi-directional counter unit. figure 15-2 shows a block diagram of the counter and its surroundings. figure 15-2. counter unit block diagram signal description (internal signals): count increment or decrement tcnt0 by 1. direction select between increment and decrement. clear clear tcnt0 (set all bits to zero). clk t n timer/counter clock, referred to as clk t0 in the following. top signalize that tcnt0 has reached maximum value. bottom signalize that tcnt0 has re ached minimum value (zero). depending of the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clk t0 ). clk t0 can be generated from an external or internal clock source, selected by the clock select bits (cs02:0). w hen no clock source is selected (cs02:0 = 0) the timer is stopped. however, the tcnt0 value can be accessed by the cpu, regardless of whether clk t0 is present or not. a cpu write overrides (has priority over) all counter clear or count operations. the counting sequence is determined by the setting of the wgm01 and wgm00 bits located in the timer/counter control register (tccr0a). there are close connections between how the counter behaves (counts) and how waveforms are generated on the output compare output oc0a. for more details about advanced count ing sequences and waveform generation, see ?modes of operation? on page 90 . the timer/counter overflow flag (tov0) is set according to the mode of operation selected by the wgm01:0 bits. tov0 can be used for generating a cpu interrupt. 15.5 output compare unit the 8 -bit comparator continuously compares tcnt0 with the output compare register (ocr0a). whenever tcnt0 equals ocr0a, the comparator signals a match. a match will set the output compare flag (ocf0a) at the next timer clock cycle. if enabled (ocie0a = 1 and global interrupt flag in sreg is set), the output compare flag generates an output compare interrupt. the ocf0a flag is automatically cleared when the interrupt is executed. alternatively, the ocf0a flag can be cleared by software by writ ing a logical one to its i/o bit location. the data b u s tcntn control logic count tovn (int.req.) clock select top tn edge detector ( from prescaler ) clk tn bottom direction clear 88 2570n?avr?05/11 atmega325/3250/645/6450 waveform generator uses the match signal to generate an output according to operating mode set by the wgm01:0 bits and compare output mode (com0a1:0) bits. the max and bottom sig- nals are used by the waveform generator for handling the special cases of the extreme values in some modes of operation ( see ?modes of operation? on page 90. ). figure 15-3 shows a block diagram of the output compare unit. figure 15-3. output compare unit, block diagram ocfn x (int.req.) = (8-bit comparator ) ocrnx ocnx data b u s tcntn wgmn1:0 waveform generator top focn comnx1:0 bottom 89 2570n?avr?05/11 atmega325/3250/645/6450 the ocr0a register is double buffered when us ing any of the pulse width modulation (pwm) modes. for the normal and clear timer on compare (ctc) modes of operation, the double buff- ering is disabled. the double buffering synchron izes the update of the ocr0 compare register to either top or bottom of the counting sequenc e. the synchronization prevents the occurrence of odd-length, non-symmetrical pwm pulses, thereby making the output glitch-free. the ocr0a register access may seem complex, but this is not case. when the double buffer- ing is enabled, the cpu has access to the ocr0 a buffer register, and if double buffering is disabled the cpu will access the ocr0a directly. 15.5.1 force output compare in non-pwm waveform generation modes, the match output of the comparator can be forced by writing a one to the fo rce output compare (foc0a) bit. fo rcing compare match will not set the ocf0a flag or reload/clear the ti mer, but the oc0a pin will be updated as if a real compare match had occurred (the com0a1:0 bits settings define whether the oc0a pin is set, cleared or toggled). 15.5.2 compare match bloc king by tcnt0 write all cpu write operations to th e tcnt0 register will block any co mpare match that occur in the next timer clock cycle, even when the timer is stopped. this feature allo ws ocr0a to be initial- ized to the same value as tcnt0 without triggering an interrupt when the timer/counter clock is enabled. 15.5.3 using the output compare unit since writing tcnt0 in any mode of operation will block all comp are matches for one timer clock cycle, there are risks involved when changing tcnt0 when using the output compare unit, independently of whether the timer/counter is running or not. if the value written to tcnt0 equals the ocr0a value, the compare match will be missed, resulting in incorrect waveform generation. similarly, do not write the tcnt0 value equal to bottom when the counter is counting down. the setup of the oc0a should be performed before setting the data direction register for the port pin to output. the easiest way of setting the oc0a value is to use the force output com- pare (foc0a) strobe bits in normal mode. the oc0a register keeps its value even when changing between waveform generation modes. be aware that the com0a1:0 bits are not double buffered together with the compare value. changing the com0a1:0 bits will take effect immediately. 15.6 compare match output unit the compare output mode (com0a1:0) bits have two functions. the waveform generator uses the com0a1:0 bits for defining the output compare (oc0a) state at the next compare match. also, the com0a1:0 bits control the oc0a pin output source. figure 15-4 shows a sim- plified schematic of the logic affected by the com0a1:0 bit setting. the i/o registers, i/o bits, and i/o pins in the figure are shown in bold. only the parts of the general i/o port control regis- ters (ddr and port) that are affected by the com0a1:0 bits are shown. when referring to the oc0a state, the reference is for the internal oc0a register, not the oc0a pin. if a system reset occur, the oc0a register is reset to ?0?. 90 2570n?avr?05/11 atmega325/3250/645/6450 figure 15-4. compare match output unit, schematic the general i/o port function is overridden by the output compare (oc0a) from the waveform generator if either of the com0a1:0 bits are set. however, the oc0a pin direction (input or out- put) is still controlled by the da ta direction register (ddr) for th e port pin. the data direction register bit for the oc0a pin (ddr_oc0a) must be set as output before the oc0a value is vis- ible on the pin. the port override function is independent of the waveform generation mode. the design of the output compare pin logic allows initialization of the oc0a state before the output is enabled. note that some com0a1:0 bit settings are reserved for certain modes of operation. see ?register description? on page 96. 15.6.1 compare output mode and waveform generation the waveform generator uses the com0a1:0 bits differently in normal, ctc, and pwm modes. for all modes, setting the com0a1:0 = 0 tells the waveform generator that no action on the oc0a register is to be performed on the next compare match. for compare output actions in the non-pwm modes refer to table 15-3 on page 97 . for fast pwm mode, refer to table 15-4 on page 97 , and for phase correct pwm refer to table 15-5 on page 9 8 . a change of the com0a1:0 bits st ate will have effect at the first compare match after the bits are written. for non-pwm modes, the action can be fo rced to have immediate effect by using the foc0a strobe bits. 15.7 modes of operation the mode of operation, i.e., the behavior of the timer/counter and the output compare pins, is defined by the combination of the waveform generation mode (wgm01:0) and compare output mode (com0a1:0) bits. the compare output mode bits do not affect the counting sequence, while the waveform generation mode bits do. the com0a1:0 bits control whether the pwm output generated should be inverted or not (inverted or non-inverted pwm). for non-pwm modes the com0a1:0 bits control whether the output should be set, cleared, or toggled at a compare match ( see ?compare match output unit? on page 8 9. ). for detailed timing information refer to figure 15- 8 , figure 15-9 , figure 15-10 and figure 15-11 in ?timer/counter timing diagrams? on page 95 . port ddr dq dq ocn pin ocnx dq waveform generator comnx1 comnx0 0 1 data b u s focn clk i/o 91 2570n?avr?05/11 atmega325/3250/645/6450 15.7.1 normal mode the simplest mode of operation is the normal mode (wgm01:0 = 0). in this mode the counting direction is always up (incrementing), and no counter clear is performed. the counter simply overruns when it passes its maximum 8 -bit value (top = 0xff) and then restarts from the bot- tom (0x00). in normal o peration the timer/counter overflow flag (tov0) will be set in the same timer clock cycle as the tcnt0 becomes zero. the tov0 flag in this case behaves like a ninth bit, except that it is only set, not cleared. however, combined with the timer overflow interrupt that automatically clears the tov0 flag, the timer resolution can be increased by software. there are no special cases to consider in the normal mode, a new counter value can be written anytime. the output compare unit can be used to generate interrupts at some given time. using the out- put compare to generate waveforms in normal mode is not recommended, since this will occupy too much of the cpu time. 15.7.2 clear timer on compare match (ctc) mode in clear timer on compare or ctc mode (wgm 01:0 = 2), the ocr0a register is used to manipulate the counter resolution. in ctc mode the counter is cleared to zero when the counter value (tcnt0) matches the ocr0a. the ocr0a defines the top value for the counter, hence also its resolution. this mode allows greater control of the compare match output frequency. it also simplifies the operation of counting external events. the timing diagram for the ctc mode is shown in figure 15-5 . the counter value (tcnt0) increases until a compare match occurs between tcnt0 and ocr0a, and then counter (tcnt0) is cleared. figure 15-5. ctc mode, timing diagram an interrupt can be generated each time the counter value reaches the top value by using the ocf0a flag. if the interrupt is enabled, the interrupt handler routine can be used for updating the top value. however, changing top to a va lue close to bottom when the counter is run- ning with none or a low prescaler value must be done with care since the ctc mode does not have the double buffering feature. if the new value written to ocr0a is lower than the current value of tcnt0, the counter will miss the compar e match. the counter will then have to count to its maximum value (0xff) and wrap around starting at 0x00 before the compare match can occur. for generating a waveform output in ctc mode, the oc0a output can be set to toggle its logical level on each compare match by setting the compare output mode bits to toggle mode (com0a1:0 = 1). the oc0a value will not be visible on the port pin unless the data direction for tcntn ocn (toggle) ocnx interrupt flag set 1 4 period 2 3 (comnx1:0 = 1) 92 2570n?avr?05/11 atmega325/3250/645/6450 the pin is set to output. the waveform ge nerated will have a ma ximum frequency of f oc0 = f clk_i/o /2 when ocr0a is set to zero (0x00). the waveform frequency is defined by the following equation: the n variable represents the prescale factor (1, 8 , 64, 256, or 1024). as for the normal mode of operation, the tov0 flag is set in the same timer clock cycle that the counter counts from max to 0x00. 15.7.3 fast pwm mode the fast pulse width modulation or fast pwm mode (wgm01:0 = 3) provides a high frequency pwm waveform generation option. the fast pwm di ffers from the other pwm option by its sin- gle-slope operation. the counter counts from bottom to max then restarts from bottom. in non-inverting compare output mode, the output compare (oc0a) is cleared on the compare match between tcnt0 and ocr0a, and set at bottom. in inverting compare output mode, the output is set on compare match and cleared at bottom. due to the single-slope operation, the operating frequency of the fast pwm mode can be twice as high as the phase correct pwm mode that use dual-slope operation. this high frequency makes the fast pwm mode well suited for power regulation, rectification, and dac app lications. high frequency a llows physically small sized external components (coils, capacitors), and therefore reduces total system cost. in fast pwm mode, the counter is incremented until the counter value matches the max value. the counter is then cleared at the following timer clock cycle. the timing diagram for the fast pwm mode is shown in figure 15-6 . the tcnt0 value is in the timing diagram shown as a his- togram for illustrating the single-slope operation. the diagram includes non-inverted and inverted pwm outputs. the small horizontal line marks on the tcnt0 slopes represent compare matches between ocr0a and tcnt0. figure 15-6. fast pwm mode, timing diagram the timer/counter overflow flag (tov0) is set each time the counter reaches max. if the inter- rupt is enabled, the interrupt handler routine can be used for updating the compare value. f ocnx f clk_i/o 2 n 1 ocrnx + () ?? ------------------------------------------------- - = tcntn ocrnx update and tovn interrupt flag set 1 period 2 3 ocnx ocnx (comnx1:0 = 2) (comnx1:0 = 3) ocrnx interrupt flag set 4 5 6 7 93 2570n?avr?05/11 atmega325/3250/645/6450 in fast pwm mode, the compare unit allows generation of pwm waveforms on the oc0a pin. setting the com0a1:0 bits to two will produce a non-inverted pwm and an inverted pwm output can be generated by setting the com0a1:0 to three (see table 15-4 on page 97 ). the actual oc0a value will only be visible on the port pin if the data direction for the port pin is set as out- put. the pwm waveform is generated by setting (or clearing) the oc0a register at the compare match between ocr0a and tcnt0, and clearing (or setting) the oc0a register at the timer clock cycle the counter is cleared (changes from max to bottom). the pwm frequency for the output can be calculated by the following equation: the n variable represents the prescale factor (1, 8 , 64, 256, or 1024). the extreme values for the ocr0a register represents special cases when generating a pwm waveform output in the fast pwm mode. if the ocr0a is set equal to bottom, the output will be a narrow spike for each max+1 timer clock cycle. setting the ocr0a equal to max will result in a constantly high or low output (depending on the polarity of the output set by the com0a1:0 bits.) a frequency (with 50% duty cycle) waveform output in fast pwm mode can be achieved by set- ting oc0a to toggle its logical level on each compare match (com0a1:0 = 1). the waveform generated will have a maximum frequency of f oc0 = f clk_i/o /2 when ocr0a is set to zero. this feature is similar to the oc0a toggle in ctc mode, except the double buffer feature of the out- put compare unit is enabled in the fast pwm mode. 15.7.4 phase correct pwm mode the phase correct pwm mode (wgm01:0 = 1) pr ovides a high resolution phase correct pwm waveform generation option. the phase correct pwm mode is based on a dual-slope operation. the counter counts repeatedly from bottom to max and then from max to bottom. in non- inverting compare output mode, the output compare (oc0a) is cleared on the compare match between tcnt0 and ocr0a while counting up, and set on the compare match while counting down. in inverting output compare mode, the operation is inverted. the dual-slope operation has lower maximum operation frequency than single slope operation. however, due to the sym- metric feature of the dual-slope pwm modes, these modes are preferred for motor control applications. the pwm resolution for the phase correct pwm m ode is fixed to eight bits. in phase correct pwm mode the counter is incremented until the counter value matches max. when the counter reaches max, it changes the count direction. the tcnt0 value will be equal to max for one timer clock cycle. the timing diagram for the phase correct pwm mode is shown on figure 15-7 . the tcnt0 value is in the timing diagram shown as a histogram for illustrating the dual-slope operation. the diagram includes non-inverted and inverted pwm outputs. the small horizontal line marks on the tcnt0 slopes represent compare matches between ocr0a and tcnt0. f ocnxpwm f clk_i/o n 256 ? ------------------ = 94 2570n?avr?05/11 atmega325/3250/645/6450 figure 15-7. phase correct pwm mode, timing diagram the timer/counter overflow flag (tov0) is set each time the counter reaches bottom. the interrupt flag can be used to generate an interrupt each time the counter reaches the bottom value. in phase correct pwm mode, the compare unit allows generation of pwm waveforms on the oc0a pin. setting the com0a1:0 bits to two will produce a non-inverted pwm. an inverted pwm output can be generated by setting the com0a1:0 to three (see table 15-5 on page 9 8 ). the actual oc0a value will only be visible on the port pin if the data direction for the port pin is set as output. the pwm waveform is generated by clearing (or setting) the oc0a register at the compare match between ocr0a and tcnt0 when the counter increments, and setting (or clearing) the oc0a register at compare match between ocr0a and tcnt0 when the counter decrements. the pwm frequency for the output when using phase correct pwm can be calcu- lated by the following equation: the n variable represents the prescale factor (1, 8 , 64, 256, or 1024). the extreme values for the ocr0a register represent special cases when generating a pwm waveform output in the phase correct pwm mode. if the ocr0a is set equal to bottom, the output will be continuously low an d if set equal to max the output will be continuously high for non-inverted pwm mode. for in verted pwm the output will have the opposite logic values. at the very start of period 2 in figure 15-7 ocn has a transition from high to low even though there is no compare match. the point of this transition is to guarantee symmetry around bot- tom. there are two cases that give a transition without compare match. ? ocr0a changes its valu e from max, like in figure 15-7 . when the ocr0a value is max the ocn pin value is the same as the result of a down-counting compare match. to ensure symmetry around bottom the ocn value at max must correspond to the result of an up- counting compare match. tovn interrupt flag set ocnx interrupt flag set 1 2 3 tcntn period ocn ocn (comnx1:0 = 2) (comnx1:0 = 3) ocrnx update f ocnxpcpwm f clk_i/o n 510 ? ------------------ = 95 2570n?avr?05/11 atmega325/3250/645/6450 ? the timer starts counting from a value higher than the one in ocr0a, and for that reason misses the compare match and hence the ocn change that would have happened on the way up. 15.8 timer/counter timing diagrams the timer/counter is a synchronous design and the timer clock (clk t0 ) is therefore shown as a clock enable signal in the following figures. the figures include information on when interrupt flags are set. figure 15- 8 contains timing data for basic timer/counter operation. the figure shows the count sequence close to the max val ue in all modes other than phase correct pwm mode. figure 15-8. timer/counter timing diagram, no prescaling figure 15-9 shows the same timing data, but with the prescaler enabled. figure 15-9. timer/counter timing dia gram, with prescaler (f clk_i/o / 8 ) figure 15-10 shows the setting of ocf0a in all modes except ctc mode. figure 15-10. timer/counter timing diagram, setting of ocf0a, with prescaler (f clk_i/o / 8 ) clk tn (clk i/o /1) tovn clk i/o tcntn max - 1 max bottom bottom + 1 tovn tcntn max - 1 max bottom bottom + 1 clk i/o clk tn (clk i/o /8) ocfnx ocrnx tcntn ocrnx value ocrnx - 1 ocrnx ocrnx + 1 ocrnx + 2 clk i/o clk tn (clk i/o /8) 96 2570n?avr?05/11 atmega325/3250/645/6450 figure 15-11 shows the setting of ocf0a and the clearing of tcnt0 in ctc mode. figure 15-11. timer/counter timing diagram, clear timer on compare match mode, with pres- caler (f clk_i/o / 8 ) 15.9 register description 15.9.1 tccr0a ? timer/counter control register a ? bit 7 ? foc0a: force output compare a the foc0a bit is only active when the wgm00 bit specifies a non-pwm mode. however, for ensuring compatibility with future devices, this bit must be set to zero when tccr0 is written when operating in pwm mode. when writing a logical one to the foc0a bit, an immediate com- pare match is forced on the waveform generation unit. the oc0a output is changed according to its com0a1:0 bits setting. note that the foc0a bit is implemented as a strobe. therefore it is the value present in the com0a1:0 bits that determines the effect of the forced compare. a foc0a strobe will not gen erate any interrupt, nor will it cl ear the timer in ctc mode using ocr0a as top. the foc0a bit is always read as zero. ? bit 6, 3 ? wgm01:0: waveform generation mode these bits control the counting sequence of the counter, the source for the maximum (top) counter value, and what type of waveform generation to be used. modes of operation supported by the timer/counter unit are: normal mode, clear timer on compare match (ctc) mode, and two types of pulse width modulation (pwm) modes. see table 15-2 and ?modes of operation? on page 90 . ocfnx ocrnx tcntn (ctc) top top - 1 top bottom bottom + 1 clk i/o clk tn (clk i/o /8) bit 7 6 5 4 3 2 1 0 0x24 (0x44) foc0a wgm00 com0a1 com0a0 wgm01 cs02 cs01 cs00 tccr0 read/write w r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 97 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. the ctc0 and pwm0 bit definition names are now obsolete. use t he wgm01:0 definitions. however, the functionality and location of these bits are compatible with previous versions of the timer. ? bit 5:4 ? com01:0: compare match output mode these bits control the output compare pin (oc0a) behavior. if one or both of the com0a1:0 bits are set, the oc0a output overrides the normal po rt functionality of the i/o pin it is connected to. however, note that the data direction r egister (ddr) bit corresponding to the oc0a pin must be set in order to enable the output driver. when oc0a is connected to the pin, the function of the com0a1:0 bits depends on the wgm01:0 bit setting. table 15-3 shows the com0a1:0 bit functionality when the wgm01:0 bits are set to a normal or ctc mode (non-pwm). table 15-4 shows the com0a1:0 bit functionality when the wgm01:0 bits are set to fast pwm mode. note: 1. a special case occurs when ocr0a equals top and com0a1 is set. in this case, the com- pare match is ignored, but the set or clear is done at top. see ?fast pwm mode? on page 92 for more details. table 15-5 shows the com0a1:0 bit functionality when the wgm01:0 bits are set to phase cor- rect pwm mode. table 15-2. waveform generation mode bit description (1) mode wgm01 (ctc0) wgm00 (pwm0) timer/counter mode of operation top update of ocr0a at tov0 flag set on 0 0 0 normal 0xff immediate max 1 0 1 pwm, phase correct 0xff top bottom 2 1 0 ctc ocr0a immediate max 31 1fast pwm 0xffbottommax table 15-3. compare output mode, non-pwm mode com0a1 com0a0 description 0 0 normal port operation, oc0a disconnected. 0 1 toggle oc0a on compare match 1 0 clear oc0a on compare match 1 1 set oc0a on compare match table 15-4. compare output mode, fast pwm mode (1) com0a1 com0a0 description 0 0 normal port operation, oc0a disconnected. 01reserved 1 0 clear oc0a on compare match, set oc0a at bottom, (non-inverting mode) 1 1 set oc0a on compare match, clear oc0a at bottom, (inverting mode.) 98 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. a special case occurs when ocr0a equals top and com0a1 is set. in this case, the com- pare match is ignored, but the set or clear is done at top. see ?phase correct pwm mode? on page 93 for more details. ? bit 2:0 ? cs02:0: clock select the three clock select bits select the clock source to be used by the timer/counter. if external pin modes are used for the timer/counter0, transitions on the t0 pin will clock the counter even if the pin is configured as an output. this feature allows software control of the counting. 15.9.2 tcnt0 ? timer/counter register the timer/counter register gives direct ac cess, both for read and write operations, to the timer/counter unit 8 -bit counter. writing to the tcnt0 register blocks (removes) the compare match on the following timer clock. modifying the counter (tcnt0) while the counter is running, introduces a risk of missing a compare match between tcnt0 and the ocr0a register. 15.9.3 ocr0a ? output compare register a table 15-5. compare output mode, phase correct pwm mode (1) com0a1 com0a0 description 0 0 normal port operation, oc0a disconnected. 01reserved 1 0 clear oc0a on compare match when up-counting. set oc0a on compare match when counting down. 1 1 set oc0a on compare match when up-counting. clear oc0a on compare match when counting down. table 15-6. clock select bit description cs02 cs01 cs00 description 0 0 0 no clock source (timer/counter stopped) 001clk i/o /(no prescaling) 010clk i/o / 8 (from prescaler) 011clk i/o /64 (from prescaler) 100clk i/o /256 (from prescaler) 101clk i/o /1024 (from prescaler) 1 1 0 external clock source on t0 pin. clock on falling edge. 1 1 1 external clock source on t0 pin. clock on rising edge. bit 76543210 0x26 (0x46) tcnt0[7:0] tcnt0 read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 0x27 (0x47) ocr0a[7:0] ocr0 read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 99 2570n?avr?05/11 atmega325/3250/645/6450 the output compare register a contains an 8 -bit value that is continuously compared with the counter value (tcnt0). a match can be used to generate an output compare interrupt, or to generate a waveform output on the oc0a pin. 15.9.4 timsk0 ? timer/counter 0 interrupt mask register ? bit 1 ? ocie0a: timer/counter0 output compare match a interrupt enable when the ocie0a bit is written to one, and the i-bit in the status register is set (one), the timer/counter0 compare match a interrupt is enabled. the corresponding interrupt is executed if a compare match in timer/coun ter0 occurs, i.e., when the ocf0a bit is set in the timer/coun- ter 0 interrupt flag register ? tifr0. ? bit 0 ? toie0: timer/counter0 overflow interrupt enable when the toie0 bit is written to one, and the i-bit in the status register is set (one), the timer/counter0 overflow interrupt is enabled. the corresponding interrupt is executed if an overflow in timer/counter0 occurs, i.e., when the tov0 bit is set in the timer/counter 0 inter- rupt flag register ? tifr0. 15.9.5 tifr0 ? timer/counter 0 interrupt flag register ? bit 1 ? ocf0a: output compare flag 0 a the ocf0a bit is set (one) when a compare match occurs between the timer/counter0 and the data in ocr0a ? output compare register0. ocf0a is cleared by hardware when executing the corresponding interrupt handling vector. alter natively, ocf0a is cleared by writing a logic one to the flag. when the i-bit in sreg, ocie0a (timer/counter0 compare match interrupt enable), and ocf0a are set (one), the timer/counter0 compare match interrupt is executed. ? bit 0 ? tov0: timer/counter0 overflow flag the bit tov0 is set (one) when an overflow occu rs in timer/counter0. tov0 is cleared by hard- ware when executing the corresponding interrupt handling vector. alternatively, tov0 is cleared by writing a logic one to the flag. when the sr eg i-bit, toie0 (timer/counter0 overflow inter- rupt enable), and tov0 are set (one), the timer/ counter0 overflow interrupt is executed. in phase correct pwm mode, this bit is set when timer/counter0 changes counting direction at 0x00. 16. timer/counter0 and ti mer/counter1 prescalers timer/counter1 and timer/counter0 share the same prescaler module, but the timer/counters can have different prescaler settings. the description below applies to both timer/counter1 and timer/counter0. bit 76543210 (0x6e) ? ? ? ? ? ?ocie0atoie0timsk0 read/writerrrrrrr/wr/w initial value 0 0 0 0 0 0 0 0 bit 76543210 0x15 (0x35) ? ? ? ? ? ?ocf0a tov0 tifr0 read/writerrrrrrr/wr/w initial value00000000 100 2570n?avr?05/11 atmega325/3250/645/6450 16.0.1 internal clock source the timer/counter can be clocked directly by the system clock (by setting the csn2:0 = 1). this provides the fastest operation, with a maximum timer/counter clock frequency equal to system clock frequency (f clk_i/o ). alternatively, one of four taps from the prescaler can be used as a clock source. the prescaled clock has a frequency of either f clk_i/o / 8 , f clk_i/o /64, f clk_i/o /256, or f clk_i/o /1024. 16.0.2 prescaler reset the prescaler is free running, i.e., operates independently of the clock select logic of the timer/counter, and it is shared by timer/counter1 and timer/counter0. since the prescaler is not affected by the timer/counter? s clock select, the state of t he prescaler will have implications for situations where a prescaled clock is used. one example of prescaling artifacts occurs when the timer is enabled and clocked by the prescaler (6 > csn2:0 > 1). the number of system clock cycles from when the timer is enabled to the first count occurs can be from 1 to n+1 system clock cycles, where n equals the prescaler divisor ( 8 , 64, 256, or 1024). it is possible to use the prescaler reset for synchronizing the timer/counter to program execu- tion. however, care must be taken if the other timer/counter that shares the same prescaler also uses prescaling. a prescaler reset will affect the prescaler period for all timer/coun ters it is connected to. 16.0.3 external clock source an external clock source applied to the t1/t0 pin can be used as timer/counter clock (clk t1 /clk t0 ). the t1/t0 pin is sampled once every system clock cycle by the pin synchronization logic. the synchronized (s ampled) signal is then passed through the edge detector. figure 1 shows a functional equivalent block diagram of the t1/t0 synchronization and edge detector logic. the registers are clocked at the po sitive edge of the internal system clock ( clk i/o ). the latch is transparent in the high period of the internal system clock. the edge detector generates one clk t1 /clk t 0 pulse for each positive (csn2:0 = 7) or negative (csn2:0 = 6) edge it detects. figure 1. t1/t0 pin sampling the synchronization and e dge detector logic introduces a de lay of 2.5 to 3.5 system clock cycles from an edge has been applied to the t1/t0 pin to the counter is updated. enabling and disabling of the clock input must be done when t1/t0 has been stable for at least one system clock cycle, otherwise it is a risk t hat a false timer/counter clock pulse is generated. each half period of the external clock applie d must be longer than one system clock cycle to ensure correct sampling. the external clock must be guaranteed to have less than half the sys- tem clock frequency (f extclk < f clk_i/o /2) given a 50/50% duty cycle. since the edge detector uses sampling, the maximum frequency of an external clock it can detect is half the sampling fre- quency (nyquist sampling theorem). however, due to variation of the system clock frequency tn_sync (to clock select logic) edge detector synchronization dq dq le dq tn clk i/o 101 2570n?avr?05/11 atmega325/3250/645/6450 and duty cycle caused by oscillator source (crystal, resonator, and capacitors) tolerances, it is recommended that maximum frequency of an external clock source is less than f clk_i/o /2.5. an external clock source can not be prescaled. figure 16-1. prescaler for timer/counter0 and timer/counter1 (1) note: 1. the synchronization logic on the input pins ( t1/t0) is shown in figure 1 . 16.1 register description 16.1.1 gtccr ? general timer/counter control register ? bit 7 ? tsm: timer/counter synchronization mode writing the tsm bit to one activates the timer/counter synchronization mode. in this mode, the value that is written to the psr2 and psr10 bits is kept, hence keeping the corresponding pres- caler reset signals asserted. this ensures that the corresponding timer/counters are halted and can be configured to the same value without the risk of one of them advancing during configura- tion. when the tsm bit is written to zero, t he psr2 and psr10 bits are cleared by hardware, and the timer/counters start counting simultaneously. ? bit 0 ? psr10: prescaler reset timer/counter1 and timer/counter0 when this bit is one, timer/co unter1 and timer/counter 0 prescaler will be reset. this bit is nor- mally cleared immediately by hardware, except if the tsm bit is set. note that timer/counter1 and timer/counter0 share the same prescaler and a reset of this prescaler will affect both timers. psr10 clear clk t1 clk t0 t1 t0 clk i/o synchronization synchronization bit 7 6 5 4 3 2 1 0 0x23 (0x43) tsm ? ? ? ? ? psr2 psr10 gtccr read/write r/w r r r r r r/w r/w initial value 0 0 0 0 0 0 0 0 102 2570n?avr?05/11 atmega325/3250/645/6450 17. 16-bit timer/counter1 17.1 features the 16-bit timer/counter unit allows accurate program execution timing (event management), wave generation, and signal timing measurement. the main features are: ? true 16-bit design (i.e., allows 16-bit pwm) ? two independent output compare units ? double buffered outp ut compare registers ? one input capture unit ? input capture noise canceler ? clear timer on compare match (auto reload) ? glitch-free, phase correct pu lse width modulator (pwm) ? variable pwm period ? frequency generator ? external event counter ? four independent interrupt sources (tov1, ocf1a, ocf1b, and icf1) 17.2 overview most register and bit references in this sect ion are written in general form. a lower case ?n? replaces the timer/counter number, and a lower case ?x? replaces the output compare unit. however, when using the register or bit defines in a program, the precise form must be used, i.e., tcnt1 for accessing timer/counter1 counter value and so on. a simplified block diagram of the 16-bit timer/counter is shown in figure 17-1 . for the actual placement of i/o pins, refer to ?pinout atmega3250/6450? on page 2 . cpu accessible i/o reg- isters, including i/o bits and i/o pins, are shown in bold. the devi ce-specific i/o register and bit locations are listed in the ?register description? on page 123 . the prtim1 bit in ?power reduction register? on page 37 must be written to zero to enable the timer/counter1 module. 103 2570n?avr?05/11 atmega325/3250/645/6450 figure 17-1. 16-bit timer/counter block diagram (1) note: 1. refer to figure 1-1 on page 2 , ?alternate functions of port d? on page 71 , and ?alternate functions of port g? on page 76 for timer/counter1 pin placement and description. 17.2.1 registers the timer/counter (tcnt1), output compare registers (ocr1a/b), and input capture regis- ter (icr1) are all 16-bit registers. special procedures must be followed when accessing the 16- bit registers. these procedures are described in the section ?accessing 16-bit registers? on page 104 . the timer/counter co ntrol registers (tccr1a/b) are 8 -bit registers and have no cpu access restrictions. interrupt requests (abbrevi ated to int.req. in the figure) signals are all visible in the timer interrupt flag register (tifr1). all interrupts are individually masked with the timer interrupt mask register (timsk1). tifr1 and timsk1 are not shown in the figure. the timer/counter can be clocked internally, via the prescaler, or by an external clock source on the t1 pin. the clock select logic block controls which clock source and edge the timer/counter uses to increment (or decrement) its value. the timer/counter is inactive when no clock source is selected. the output from the clock select logic is referred to as the timer clock (clk t 1 ). the double buffered output compare registers (ocr1a/b) are compared with the timer/coun- ter value at all time. the result of the compare can be used by the waveform generator to generate a pwm or variable frequency output on the output compare pin (oc1a/b). see ?out- clock select timer/counter data b u s ocrna ocrnb icrn = = tcntn waveform generation waveform generation ocna ocnb noise canceler icpn = fixed top values edge detector control logic = 0 top bottom count clear direction tovn (int.req.) ocna (int.req.) ocnb (int.req.) icfn (int.req.) tccrna tccrnb ( from analog comparator ouput ) tn edge detector ( from prescaler ) clk tn 104 2570n?avr?05/11 atmega325/3250/645/6450 put compare units? on page 111. the compare match event will also set the compare match flag (ocf1a/b) which can be used to generate an output compare interrupt request. the input capture register can capture the timer/ counter value at a given external (edge trig- gered) event on either the input capture pin (icp1) or on the analog comparator pins ( see ?analog comparator? on page 197. ) the input capture unit includes a digital filtering unit (noise canceler) for reducing the chance of capturing noise spikes. the top value, or maximum timer/counter value, can in some modes of operation be defined by either the ocr1a register, the icr1 regist er, or by a set of fixed values. when using ocr1a as top value in a pwm mode, the ocr1a register can not be used for generating a pwm output. however, the top value will in this case be do uble buffered allowing the top value to be changed in run time. if a fixed top value is required, the icr1 register can be used as an alternative, freeing the ocr1a to be used as pwm output. 17.2.2 definitions the following definitions are used extensively throughout the section: 17.2.3 compatibility the 16-bit timer/counter has been updated and impr oved from previous versions of the 16-bit avr timer/counter. this 16-bit timer/counter is fully compatible with the earlier version regarding: ? all 16-bit timer/counter related i/o register address locations, including timer interrupt registers. ? bit locations inside all 16-bit timer/counter registers, including timer interrupt registers. ? interrupt vectors. the following control bits have changed name, but have same functionality and register location: ? pwm10 is changed to wgm10. ? pwm11 is changed to wgm11. ? ctc1 is changed to wgm12. the following bits are added to the 16-bit timer/counter control registers: ? foc1a and foc1b are added to tccr1c. ? wgm13 is added to tccr1b. the 16-bit timer/counter has improvements that will affect the compatibility in some special cases. 17.3 accessing 16-bit registers the tcnt1, ocr1a/b, and icr1 are 16-bit registers that can be accessed by the avr cpu via the 8 -bit data bus. the 16-bit register must be byte accessed using two read or write operations. each 16-bit timer has a single 8 -bit register for temporary storing of the high byte of the 16-bit table 17-1. definitions of timer/counter values. bottom the counter reaches the bottom when it becomes 0x0000. max the counter reaches its max imum when it becomes 0xffff (decimal 65535). top the counter reaches the top when it becomes equal to the highest value in the count sequence. the top value can be assigned to be one of the fixed values: 0x00ff, 0x01ff, or 0x03ff, or to the value stored in the ocr1a or icr1 regis- ter. the assignment is dependent of the mode of operation. 105 2570n?avr?05/11 atmega325/3250/645/6450 access. the same temporary register is shared between all 16-bit registers within each 16-bit timer. accessing the low byte triggers the 16-bit read or write operation. when the low byte of a 16-bit register is written by the cpu, the high byte stored in the temporary register, and the low byte written are both copied into the 16-bit register in the same clock cycle. when the low byte of a 16-bit register is read by the cpu, the high by te of the 16-bit register is copied into the tempo- rary register in the same clock cycle as the low byte is read. not all 16-bit accesses uses the temporary register for the high byte. reading the ocr1a/b 16- bit registers does not involve using the temporary register. to do a 16-bit write, the high byte must be written before the low byte. for a 16-bit read, the low byte must be read before the high byte. the following code examples show how to access the 16-bit timer registers assuming that no interrupts updates the temporary register. the same principle can be used directly for accessing the ocr1a/b and icr1 registers. note that when using ?c?, the compiler handles the 16-bit access. note: 1. see ?about code examples? on page 9 . the assembly code example returns the tcnt1 value in the r17:r16 register pair. it is important to notice that accessing 16-bit registers are atomic operations. if an interrupt occurs between the two instructions accessing the 16-bit register, and the interrupt code updates the temporary register by accessing the same or any other of the 16-bit timer regis- ters, then the result of the a ccess outside the interrupt will be corrupted. theref ore, when both the main code and the interrupt code update the temporary register, the main code must disable the interrupts during the 16-bit access. assembly code examples (1) ... ; set tcnt 1 to 0x01ff ldi r17,0x01 ldi r16,0xff out tcnt 1 h,r17 out tcnt 1 l,r16 ; read tcnt 1 into r17:r16 in r16,tcnt 1 l in r17,tcnt 1 h ... c code examples (1) unsigned int i; ... /* set tcnt 1 to 0x01ff */ tcnt 1 = 0x1ff; /* read tcnt 1 into i */ i = tcnt 1 ; ... 106 2570n?avr?05/11 atmega325/3250/645/6450 the following code examples show how to do an atomic read of the tcnt1 register contents. reading any of the ocr1a/b or icr1 registers can be done by using the same principle. note: 1. see ?about code examples? on page 9 . the assembly code example returns the tcnt1 value in the r17:r16 register pair. assembly code example (1) tim16_readtcnt 1 : ; save global interrupt flag in r18,sreg ; disable interrupts cli ; read tcnt 1 into r17:r16 in r16,tcnt 1 l in r17,tcnt 1 h ; restore global interrupt flag out sreg,r18 ret c code example (1) unsigned int tim16_readtcnt 1 ( void ) { unsigned char sreg; unsigned int i; /* save global interrupt flag */ sreg = sreg; /* disable interrupts */ __disable_interrupt(); /* read tcnt 1 into i */ i = tcnt 1 ; /* restore global interrupt flag */ sreg = sreg; return i; } 107 2570n?avr?05/11 atmega325/3250/645/6450 the following code examples show how to do an atomic write of the tcnt1 register contents. writing any of the ocr1a/b or icr1 register s can be done by using the same principle. note: 1. see ?about code examples? on page 9 . the assembly code example requires that the r17:r16 register pair contains the value to be writ- ten to tcnt1. 17.3.1 reusing the temporary high byte register if writing to more than one 16-bit register where the high byte is the same for all registers written, then the high byte only needs to be written once. however, note that the same rule of atomic operation described previously also applies in this case. 17.4 timer/counter clock sources the timer/counter can be clocked by an internal or an external clock source. the clock source is selected by the clock select logic which is controlled by the clock select (cs12:0) bits located in the timer/counter control register b (tccr1b). for details on clock sources and prescaler, see ?timer/counter0 and timer/counter1 prescalers? on page 99 . assembly code example (1) tim16_writetcnt 1 : ; save global interrupt flag in r18,sreg ; disable interrupts cli ; set tcnt 1 to r17:r16 out tcnt 1 h,r17 out tcnt 1 l,r16 ; restore global interrupt flag out sreg,r18 ret c code example (1) void tim16_writetcnt 1 ( unsigned int i ) { unsigned char sreg; unsigned int i; /* save global interrupt flag */ sreg = sreg; /* disable interrupts */ __disable_interrupt(); /* set tcnt 1 to i */ tcnt 1 = i; /* restore global interrupt flag */ sreg = sreg; } 108 2570n?avr?05/11 atmega325/3250/645/6450 17.5 counter unit the main part of the 16-bit timer/counter is th e programmable 16-bit bi-directional counter unit. figure 17-2 shows a block diagram of the counter and its surroundings. figure 17-2. counter unit block diagram signal description (internal signals): count increment or decrement tcnt1 by 1. direction select between increment and decrement. clear clear tcnt1 (set all bits to zero). clk t 1 timer/counter clock. top signalize that tcnt1 has reached maximum value. bottom signalize that tcnt1 has re ached minimum value (zero). the 16-bit counter is mapped into two 8 -bit i/o memory locations: counter high (tcnt1h) con- taining the upper eight bits of the counter, and counter low (tcnt1l) containing the lower eight bits. the tcnt1h register can only be indirect ly accessed by the cpu. when the cpu does an access to the tcnt1h i/o location, the cpu accesses the high byte temporary register (temp). the temporary register is updated with the tcnt1h value when the tcnt1l is read, and tcnt1h is updated with the temporary register va lue when tcnt1l is written. this allows the cpu to read or write the entire 16-bit counter value within one clock cycle via the 8 -bit data bus. it is important to notice that there are special cases of writing to the tcnt1 register when the counter is counting that will gi ve unpredictable results. the s pecial cases are described in the sections where they are of importance. depending on the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clk t 1 ). the clk t 1 can be generated from an external or internal clock source, selected by the clock select bits (cs12:0). when no clock source is selected (cs12:0 = 0) the timer is stopped. however, the tcnt1 value can be accessed by the cpu, independent of whether clk t 1 is present or not. a cpu write overrides (has priority over) all counter clear or count operations. the counting sequence is determined by the setting of the waveform generation mode bits (wgm13:0) located in the timer/counter control registers a and b (tccr1a and tccr1b). there are close connections between how the counter behaves (counts) and how waveforms are generated on the output compare outputs oc1x. for more details about advanced counting sequences and waveform generation, see ?modes of operation? on page 114 . temp (8-bit) data bus (8-bit) tcntn (16-bit counter) tcntnh (8-bit) tcntnl (8-bit) control logic count clear direction tovn (int.req.) clock select top bottom tn edge detector ( from prescaler ) clk tn 109 2570n?avr?05/11 atmega325/3250/645/6450 the timer/counter overflow flag (tov1) is set according to the mode of operation selected by the wgm13:0 bits. tov1 can be used for generating a cpu interrupt. 17.6 input capture unit the timer/counter incorporates an input capture unit that can capture external events and give them a time-stamp indicating time of occurrence. the external signal indicating an event, or mul- tiple events, can be applied via the icp1 pin or al ternatively, via the analog-comparator unit. the time-stamps can then be used to calculate frequenc y, duty-cycle, and other features of the sig- nal applied. alternatively the time-stamps can be used for creating a log of the events. the input capture unit is illustrated by the block diagram shown in figure 17-3 . the elements of the block diagram that are not directly a part of the input capture unit are gray shaded. the small ?n? in register and bit names indicates the timer/counter number. figure 17-3. input capture unit block diagram when a change of the logic level (an event) occurs on the input capture pin (icp1), alternatively on the analog comparator output (aco), and this change confirms to the setting of the edge detector, a capture will be triggered. when a captur e is triggered, the 16-bit value of the counter (tcnt1) is written to the input capture register (icr1). the input capture flag (icf1) is set at the same system clock as the tcnt1 value is copi ed into icr1 register. if enabled (icie1 = 1), the input capture flag generates an input capture interrupt. the icf1 flag is automatically cleared when the interrupt is executed. alternatively the icf1 flag can be cleared by software by writing a logical one to its i/o bit location. reading the 16-bit value in the input capture register (icr1) is done by first reading the low byte (icr1l) and then the high byte (icr1h). when the low byte is read the high byte is copied into the high byte temporary regi ster (temp). when the cpu reads the icr1h i/o location it will access the temp register. the icr1 register can only be written when us ing a waveform generation mode that utilizes the icr1 register for defining the counter?s top value. in these cases the waveform genera- icfn (int.req.) analog comparator write icrn (16-bit register) icrnh (8-bit) noise canceler icpn edge detector temp (8-bit) data bus (8-bit) icrnl (8-bit) tcntn (16-bit counter) tcntnh (8-bit) tcntnl (8-bit) acic* icnc ices aco* 110 2570n?avr?05/11 atmega325/3250/645/6450 tion mode (wgm13:0) bits must be set before the top value can be written to the icr1 register. when writing the icr1 re gister the high byte must be written to the icr1h i/o location before the low byte is written to icr1l. for more information on how to access the 16-bit registers refer to ?accessing 16-bit registers? on page 104 . 17.6.1 input capture trigger source the main trigger source for the input capture unit is the input capture pin (icp1). timer/counter1 can alternatively use the analog comparator output as trigger source for the input capture unit. the analog comparator is selected as trigger source by setting the analog comparator input capture (acic) bit in the analog comparator control and status register (acsr). be aware that changing trigger source can trigger a capture. the input capture flag must therefore be cleared after the change. both the input capture pin (icp1) and the analog comparator output (aco) inputs are sampled using the same technique as for the t1 pin ( figure 1 on page 100 ). the edge detector is also identical. however, when the noise canceler is enabled, additional logic is inserted before the edge detector, which increases t he delay by four system clock cycles. note that the input of the noise canceler and edge detector is always enabl ed unless the timer/counter is set in a wave- form generation mode that uses icr1 to define top. an input capture can be trigger ed by software by controlling the port of the icp1 pin. 17.6.2 noise canceler the noise canceler improves noise immunity by using a simple digital filtering scheme. the noise canceler input is monitored over four samples, and all four must be equal for changing the output that in turn is used by the edge detector. the noise canceler is enabled by setting the input capture noise canceler (icnc1) bit in timer/counter control register b (tccr1b). when enabled the noise canceler introduces addi- tional four system clock cycles of delay from a change applied to the input, to the update of the icr1 register. the noise canceler uses the sy stem clock and is therefore not affected by the prescaler. 17.6.3 using the input capture unit the main challenge when using the input capture unit is to assign enough processor capacity for handling the incoming events. the time between two events is critical. if the processor has not read the captured value in th e icr1 register before the nex t event occurs, the icr1 will be overwritten with a new value. in this case the result of the ca pture will be incorrect. when using the input capture interrupt, the icr1 register should be read as early in the inter- rupt handler routine as possible. even though the input capture interrupt has relatively high priority, the maximum interrupt response time is dependent on the maximum number of clock cycles it takes to handle any of the other interrupt requests. using the input capture unit in any mode of operation when the top value (resolution) is actively changed during operation, is not recommended. measurement of an external signal?s duty cycle requires that the trigger edge is changed after each capture. changing the edge sensing must be done as early as possible after the icr1 register has been read. after a change of the edge, the input capture flag (icf1) must be 111 2570n?avr?05/11 atmega325/3250/645/6450 cleared by software (writing a logical one to the i/o bit location). for measuring frequency only, the clearing of the icf1 flag is not required (if an interrupt handler is used). 17.7 output compare units the 16-bit comparator continuously compares tcnt1 with the output compare register (ocr1x). if tcnt equals ocr1x the comparator signals a match. a match will set the output compare flag (ocf1x) at the next timer clock cycle. if enabled (ocie1x = 1), the output com- pare flag generates an output compare interrupt. the ocf1x flag is automatically cleared when the interrupt is executed. alternatively the ocf1x flag can be cleared by software by writ- ing a logical one to its i/o bit location. the waveform generator uses the match signal to generate an output according to operating mode set by the waveform generation mode (wgm13:0) bits and compare output mode (com1x1:0) bits. the top and bottom signals are used by the waveform generator for handling the special cases of the extreme values in some modes of operation ( see ?modes of operation? on page 114. ) a special feature of output compare unit a allows it to define the timer/counter top value (i.e., counter resolution). in addition to the counter resolution, the top value defines the period time for waveforms generated by the waveform generator. figure 17-4 shows a block diagram of the output compare unit. the small ?n? in the register and bit names indicates the device number (n = 1 for timer/counter 1), and the ?x? indicates output compare unit (a/b). the elements of the block diagram that are not directly a part of the output compare unit are gray shaded. figure 17-4. output compare unit, block diagram the ocr1x register is double buffered when using any of the twelve pulse width modulation (pwm) modes. for the normal and clear timer on compare (ctc) modes of operation, the double buffering is disabled. the double buffering synchronizes the update of the ocr1x com- pare register to either top or bottom of the counting sequence. the synchronization ocfnx (int.req.) = (16-bit comparator ) ocrnx buffer (16-bit register) ocrnxh buf. (8-bit) ocnx temp (8-bit) data bus (8-bit) ocrnxl buf. (8-bit) tcntn (16-bit counter) tcntnh (8-bit) tcntnl (8-bit) comnx1:0 wgmn3:0 ocrnx (16-bit register) ocrnxh (8-bit) ocrnxl (8-bit) waveform generator top bottom 112 2570n?avr?05/11 atmega325/3250/645/6450 prevents the occurrence of odd-length, non-symmetrical pwm pulses, thereby making the out- put glitch-free. the ocr1x register access may seem complex, but this is not case. when the double buffering is enabled, the cpu has access to the ocr1x buffer register, and if double buffering is dis- abled the cpu will access the ocr1x directly. the content of the ocr1x (buffer or compare) register is only changed by a write operation (the timer/counter does not update this register automatically as the tcnt1 and icr1 register). therefore ocr1x is not read via the high byte temporary register (temp). however, it is a good practice to read the low byte first as when accessing other 16-bit registers. writing the ocr1x registers must be done via the temp reg- ister since the compare of all 16 bits is done continuously. the high byte (ocr1xh) has to be written first. when the high byte i/o location is written by the cpu, the temp register will be updated by the value written. then when the low by te (ocr1xl) is written to the lower eight bits, the high byte will be copied into the upper 8 -bits of either the ocr1x buffer or ocr1x compare register in the same system clock cycle. for more information of how to access the 16-bit registers refer to ?accessing 16-bit registers? on page 104 . 17.7.1 force output compare in non-pwm waveform generation modes, the match output of the comparator can be forced by writing a one to the force output compare (foc1x) bit. forcing compare match will not set the ocf1x flag or reload/clear the timer, but the oc1x pin will be updated as if a real compare match had occurred (the com11:0 bits settings define whether the oc1x pin is set, cleared or toggled). 17.7.2 compare match bloc king by tcnt1 write all cpu writes to the tcnt1 register will block any compare match that o ccurs in the next timer clock cycle, even when the timer is stopped. this feature allows ocr1x to be initialized to the same value as tcnt1 without triggering an inte rrupt when the timer/counter clock is enabled. 17.7.3 using the output compare unit since writing tcnt1 in any mode of operation will block all comp are matches for one timer clock cycle, there are risks involved when changing tcnt1 when using any of the output compare units, independent of whether the timer/counter is running or not. if the value written to tcnt1 equals the ocr1x value, the compare match will be missed, resulting in incorrect waveform generation. do not write the tcnt1 equal to to p in pwm modes with variable top values. the compare match for the top will be ignored and the counter will c ontinue to 0xffff. similarly, do not write the tcnt1 value equal to bottom when the counter is counting down. the setup of the oc1x should be performed before setting the data direction register for the port pin to output. the easiest way of setting the oc1x value is to use the force output com- pare (foc1x) strobe bits in normal mode. the oc1x register keeps its value even when changing between waveform generation modes. be aware that the com1x1:0 bits are not doubl e buffered together with the compare value. changing the com1x1:0 bits will take effect immediately. 17.8 compare match output unit the compare output mode (com1x1:0) bits have two functions. the waveform generator uses the com1x1:0 bits for defining the output compare (oc1x) state at the next compare match. 113 2570n?avr?05/11 atmega325/3250/645/6450 secondly the com1x1:0 bits control the oc1x pin output source. figure 17-5 shows a simplified schematic of the logic affected by the com1x1:0 bit setting. the i/o registers, i/o bits, and i/o pins in the figure are shown in bold. only the parts of the general i/o port control registers (ddr and port) that are affected by the com1x1:0 bits are shown. when referring to the oc1x state, the reference is for the internal oc1x register, not the oc1x pin. if a system reset occur, the oc1x register is reset to ?0?. figure 17-5. compare match output unit, schematic the general i/o port function is overridden by the output compare (oc1x) from the waveform generator if either of the com1x1:0 bits are set. however, the oc1x pin direction (input or out- put) is still controlled by the data direction register (ddr) for the port pin. the data direction register bit for the oc1x pin (ddr_oc1x) must be set as output before the oc1x value is visi- ble on the pin. the port override function is generally independent of the waveform generation mode, but there are some exceptions. refer to table 17-2 , table 17-3 and table 17-4 for details. the design of the output compare pin logic allows initialization of the oc1x state before the out- put is enabled. note that some com1x1:0 bi t settings are reserved for certain modes of operation. see ?register description? on page 123. the com1x1:0 bits have no effect on the input capture unit. 17.8.1 compare output mode and waveform generation the waveform generator uses the com1x1:0 bits differently in normal, ctc, and pwm modes. for all modes, setting the com1x1:0 = 0 tells the waveform generator that no action on the oc1x register is to be performed on the next compare match. for compare output actions in the non-pwm modes refer to table 17-2 on page 123 . for fast pwm mode refer to table 17-3 on page 124 , and for phase correct and phase and frequency correct pwm refer to table 17-4 on page 124 . port ddr dq dq ocnx pin ocnx dq waveform generator comnx1 comnx0 0 1 data b u s focnx clk i/o 114 2570n?avr?05/11 atmega325/3250/645/6450 a change of the com1x1:0 bits st ate will have effect at the first compare matc h after the bits are written. for non-pwm modes, the action can be fo rced to have immediate effect by using the foc1x strobe bits. 17.9 modes of operation the mode of operation, i.e., the behavior of the timer/counter and the output compare pins, is defined by the combination of the waveform generation mode (wgm13:0) and compare output mode (com1x1:0) bits. the compare output mode bits do not affect the counting sequence, while the waveform generation mode bits do. the com1x1:0 bits control whether the pwm out- put generated should be inverted or not (inverted or non-inverted pwm). for non-pwm modes the com1x1:0 bits control whether the output should be set, cleared or toggle at a compare match ( see ?compare match output unit? on page 112. ) for detailed timing information refer to ?timer/counter timing diagrams? on page 121 . 17.9.1 normal mode the simplest mode of operation is the normal mode (wgm13:0 = 0). in this mode the counting direction is always up (incrementing), and no counter clear is performed. the counter simply overruns when it passes its maximum 16-bit value (max = 0xffff) and then restarts from the bottom (0x0000). in normal operation the timer/counter overflow flag (tov1) will be set in the same timer clock cycle as the tcnt1 become s zero. the tov1 flag in this case behaves like a 17th bit, except that it is only set, not cleared. however, combined with the timer overflow interrupt that automatically clears the tov1 flag, the timer resolution can be increased by soft- ware. there are no special cases to consider in the normal mode, a new counter value can be written anytime. the input capture unit is easy to use in normal mode. however, observe that the maximum interval between the external events must not exceed the resolution of the counter. if the interval between events are too long, the timer overflow interrupt or the prescaler must be used to extend the resolution for the capture unit. the output compare units can be used to generat e interrupts at some given time. using the output compare to gene rate waveforms in norm al mode is not recommended, since this will occupy too much of the cpu time. 17.9.2 clear timer on compare match (ctc) mode in clear timer on compare or ctc mode (wgm13:0 = 4 or 12), the ocr1a or icr1 register are used to manipulate the counter resolution. in ctc mode the counter is cleared to zero when the counter value (tcnt1) matches either the ocr1a (wgm13:0 = 4) or the icr1 (wgm13:0 = 12). the ocr1a or icr1 define the top value for the counter, hence also its resolution. this mode allows greater control of the compare match output frequency. it also simplifies the opera- tion of counting external events. the timing diagram for the ctc mode is shown in figure 17-6 . the counter value (tcnt1) increases until a compare match occurs with either ocr1a or icr1, and then counter (tcnt1) is cleared. 115 2570n?avr?05/11 atmega325/3250/645/6450 figure 17-6. ctc mode, timing diagram an interrupt can be generated at each time the counter value reaches the top value by either using the ocf1a or icf1 flag according to the register used to define the top value. if the interrupt is enabled, the interrupt handler routine can be used for updating the top value. how- ever, changing the top to a value close to bottom when the counter is running with none or a low prescaler value must be done with care since the ctc mode does not have the double buff- ering feature. if the new value written to ocr1a or icr1 is lower than the current value of tcnt1, the counter will miss the co mpare match. the counter will then have to count to its max- imum value (0xffff) and wrap around starting at 0x0000 before the compare match can occur. in many cases this feature is no t desirable. an alternative will th en be to use the fast pwm mode using ocr1a for defining top (w gm13:0 = 15) since the ocr1a then will be doub le buffered. for generating a waveform output in ctc mode, the oc1a output can be set to toggle its logical level on each compare match by setting the compare output mode bits to toggle mode (com1a1:0 = 1). the oc1a value will not be visible on the port pin unless the data direction for the pin is set to output (ddr_oc1a = 1). th e waveform generated will have a maximum fre- quency of f oc 1 a = f clk_i/o /2 when ocr1a is set to zero (0x0000). the waveform frequency is defined by the following equation: the n variable represents the prescaler factor (1, 8 , 64, 256, or 1024). as for the normal mode of operation, the tov1 flag is set in the same timer clock cycle that the counter counts from max to 0x0000. 17.9.3 fast pwm mode the fast pulse width modulation or fast pwm mode (wgm13:0 = 5, 6, 7, 14, or 15) provides a high frequency pwm waveform generation option. the fast pwm differs from the other pwm options by its single-slope operation. the counter counts from bottom to top then restarts from bottom. in non-inverting compare output mode, the output compare (oc1x) is cleared on the compare match between tcnt1 and ocr1x, and set at bottom. in inverting compare output mode output is set on compare match and cleared at bottom. due to the single-slope operation, the operating frequency of the fast pwm mode can be twice as high as the phase cor- rect and phase and frequency correct pwm modes that use dual-slope operation. this high frequency makes the fast pwm mode well suited for power regula tion, rectification, and dac applications. high frequency allows physically sm all sized external com ponents (coils, capaci- tors), hence reduces total system cost. tcntn ocna (toggle) ocna interrupt flag set or icfn interrupt flag set (interrupt on top) 1 4 period 2 3 (comna1:0 = 1) f ocna f clk_i/o 2 n 1 ocrna + () ?? -------------------------------------------------- - = 116 2570n?avr?05/11 atmega325/3250/645/6450 the pwm resolution for fast pwm can be fixed to 8 -, 9-, or 10-bit, or defined by either icr1 or ocr1a. the minimum resolution allowed is 2-bit (icr1 or ocr1a set to 0x0003), and the max- imum resolution is 16-bit (icr1 or ocr1a set to max). the pwm resolution in bits can be calculated by using the following equation: in fast pwm mode the counter is incremented until the counter value matches either one of the fixed values 0x00ff, 0x01ff, or 0x03ff (wgm13:0 = 5, 6, or 7), the value in icr1 (wgm13:0 = 14), or the value in ocr1a (wgm13:0 = 15). the counter is then cleared at the following timer clock cycle. the timing diagram for the fast pwm mode is shown in figure 17-7 . the figure shows fast pwm mode when ocr1a or icr1 is us ed to define top. the tcnt1 value is in the timing diagram shown as a histogram for illu strating the single-slope operation. the diagram includes non-inverted and inverted pwm outputs. the small horizontal line marks on the tcnt1 slopes represent compare matches between ocr1x and tcnt1. the oc1x interrupt flag will be set when a compare match occurs. figure 17-7. fast pwm mode, timing diagram the timer/counter overflow flag (tov1) is set each time the counter reaches top. in addition the oc1a or icf1 flag is set at the same time r clock cycle as tov1 is set when either ocr1a or icr1 is used for defining the top value. if one of the interrupts are enabled, the interrupt han- dler routine can be used for updating the top and compare values. when changing the top value the program must ensure that the new top value is higher or equal to the value of all of the compare registers. if the top value is lower than any of the compare registers, a compare match will never occur between the tcnt1 and the ocr1x. note that when using fixed top values the unused bits are masked to zero when any of the ocr1x registers are written. the procedure for updating icr1 differs from updating ocr1a when used for defining the top value. the icr1 register is not double buffered. this means that if icr1 is changed to a low value when the counter is running with none or a low prescaler value, there is a risk that the new icr1 value written is lower than the current va lue of tcnt1. the result will then be that the counter will miss the compare matc h at the top value. the counter will then have to count to the max value (0xffff) and wrap around starting at 0x0000 before the compare match can occur. the ocr1a register however, is double buffered. this feature allows the ocr1a i/o location r fpwm top 1 + () log 2 () log ---------------------------------- - = tcntn ocrnx / top update and tovn interrupt flag set and ocna interrupt flag set or icfn interrupt flag set (interrupt on top) 1 7 period 2 3 4 5 6 8 ocnx ocnx (comnx1:0 = 2) (comnx1:0 = 3) 117 2570n?avr?05/11 atmega325/3250/645/6450 to be written anytime. when the ocr1a i/o location is written the value written will be put into the ocr1a buffer register. th e ocr1a compare register will th en be updated with the value in the buffer register at the next timer clo ck cycle the tcnt1 matches top. the update is done at the same timer clock cycle as the tcnt 1 is cleared and the tov1 flag is set. using the icr1 register for defining top work s well when using fixed top values. by using icr1, the ocr1a register is free to be used for generating a pwm output on oc1a. however, if the base pwm frequency is actively change d (by changing the top value), using the ocr1a as top is clearly a better choice due to its double buffer feature. in fast pwm mode, the compare units allow generation of pwm waveforms on the oc1x pins. setting the com1x1:0 bits to two will produce a non-inverted pwm and an inverted pwm output can be generated by setting the com1x1:0 to three (see table 17-3 on page 124 ). the actual oc1x value will only be visible on the port pin if th e data direction for the po rt pin is set as output (ddr_oc1x). the pwm waveform is generated by setting (or clearing) the oc1x register at the compare match between ocr1x and tcnt1, and clearing (or setting) the oc1x register at the timer clock cycle the counter is cleared (changes from top to bottom). the pwm frequency for the output can be calculated by the following equation: the n variable represents the prescaler divider (1, 8 , 64, 256, or 1024). the extreme values for the ocr1x register represents special cases when generating a pwm waveform output in the fast pwm mode. if the ocr1x is set equal to bottom (0x0000) the out- put will be a narrow spike for eac h top+1 timer clock cycle. se tting the ocr1x equal to top will result in a const ant high or low output (depending on the polarity of the output set by the com1x1:0 bits.) a frequency (with 50% duty cycle) waveform output in fast pwm mode can be achieved by set- ting oc1a to toggle its logical level on each compare match (com1a1:0 = 1). this applies only if ocr1a is used to define the top value (wgm 13:0 = 15). the wave form generated will have a maximum frequency of f oc 1 a = f clk_i/o /2 when ocr1a is set to zero (0x0000). this feature is similar to the oc1a toggle in ctc mode, except the double buffer feature of the output com- pare unit is enabled in the fast pwm mode. 17.9.4 phase correct pwm mode the phase correct pulse width modulation or phase correct pwm mode (wgm13:0 = 1, 2, 3, 10, or 11) provides a high resolution phase correct pwm waveform generation option. the phase correct pwm mode is, like the phase and frequency correct pwm mode, based on a dual- slope operation. the counter counts repeatedly from bottom (0x0000) to top and then from top to bottom. in non-inverting compare output mode, the output compare (oc1x) is cleared on the compare match between tcnt1 and ocr1x while counting up, and set on the compare match while counting down. in inverting output compare mode, the operation is inverted. the dual-slope operation has lower maximum operation frequency than single slope operation. however, due to the symmetric feat ure of the dual-slope pwm modes, these modes are preferred for motor control applications. the pwm resolution for the phase correct pwm mode can be fixed to 8 -, 9-, or 10-bit, or defined by either icr1 or ocr1a. the minimum resolution allowed is 2-bit (icr1 or ocr1a set to f ocnxpwm f clk_i/o n 1 top + () ? ---------------------------------- - = 118 2570n?avr?05/11 atmega325/3250/645/6450 0x0003), and the maximum resolution is 16-bit (icr1 or ocr1a set to max). the pwm resolu- tion in bits can be calculated by using the following equation: in phase correct pwm mode the counter is incremented until the counter value matches either one of the fixed values 0x00ff, 0x01ff, or 0x03ff (wgm13:0 = 1, 2, or 3), the value in icr1 (wgm13:0 = 10), or the value in ocr1a (wgm13:0 = 11). the counter has then reached the top and changes the count direct ion. the tcnt1 value will be equa l to top for one timer clock cycle. the timing diagram for the phase correct pwm mode is shown on figure 17- 8 . the figure shows phase correct pwm mode when ocr1a or icr1 is used to define top. the tcnt1 value is in the timing diagram shown as a histogram for illustrati ng the dual-slope operation. the diagram includes non-inverted and inverted pwm outputs. the small horizontal line marks on the tcnt1 slopes represent compare matches between ocr1x and tcnt1. the oc1x inter- rupt flag will be set when a compare match occurs. figure 17-8. phase correct pwm mode, timing diagram the timer/counter overflow flag (tov1) is set each time the counter reaches bottom. when either ocr1a or icr1 is used for defining the top value, the oc1a or icf1 flag is set accord- ingly at the same timer clock cycle as the ocr1x registers are updated with the double buffer value (at top). the interrupt flags can be used to generate an interrupt each time the counter reaches the top or bottom value. when changing the top value the program must ensure that the new top value is higher or equal to the value of all of the compare registers. if the top value is lower than any of the compare registers, a compare match will never occur between the tcnt1 and the ocr1x. note that when using fixed top values, the unus ed bits are masked to zero when any of the ocr1x registers are written. as the third period shown in figure 17- 8 illustrates, changing the top actively while the timer/counter is running in the phase correct mode can result in an unsymmetrical output. the reason for this can be found in the time of update of the ocr1x reg- ister. since the ocr1x update occurs at top, the pwm period starts and ends at top. this r pcpwm top 1 + () log 2 () log ---------------------------------- - = ocrnx/top update and ocna interrupt flag set or icfn interrupt flag set (interrupt on top) 1 2 3 4 tovn interrupt flag set (interrupt on bottom) tcntn period ocnx ocnx (comnx1:0 = 2) (comnx1:0 = 3) 119 2570n?avr?05/11 atmega325/3250/645/6450 implies that the length of the falling slope is determined by the previous top value, while the length of the rising slope is determined by th e new top value. when these two values differ the two slopes of the period will differ in length. the difference in length gives the unsymmetrical result on the output. it is recommended to use the phase and frequency correct mode instead of the phase correct mode when changing the top value while the timer/counter is running. when using a static top value there are practically no differences between the two modes of operation. in phase correct pwm mode, the compare units allow generation of pwm waveforms on the oc1x pins. setting the com1x1:0 bits to tw o will produce a non-inverte d pwm and an inverted pwm output can be generated by setting the com1x1:0 to three (see table 1 on page 124 ). the actual oc1x value will only be visible on the port pin if the data direction for the port pin is set as output (ddr_oc1x). the pwm waveform is gene rated by setting (or clearing) the oc1x register at the compare match between ocr1x and tcnt1 when the counter increments, and clearing (or setting) the oc1x register at compare match between ocr1x and tcnt1 when the counter decrements. the pwm frequency for the output when using phase correct pwm can be calculated by the following equation: the n variable represents the prescaler divider (1, 8 , 64, 256, or 1024). the extreme values for the ocr1x register represent special cases when generating a pwm waveform output in the phase correct pwm mode. if the ocr1x is set equal to bottom the output will be continuously low and if set equal to top the output will be continuously high for non-inverted pwm mode. for in verted pwm the output will have the opposite logic values. if ocr1a is used to define the top value (wgm13:0 = 11) and com1a1:0 = 1, the oc1a output will toggle with a 50% duty cycle. 17.9.5 phase and frequency correct pwm mode the phase and frequency correct pulse width modulation, or phase and frequency correct pwm mode (wgm13:0 = 8 or 9) provides a high resolution phase and frequency correct pwm wave- form generation option. the phase and frequency correct pwm mode is, like the phase correct pwm mode, based on a dual-slope operation. the counter counts repeatedly from bottom (0x0000) to top and then from top to bottom. in non-inverting compare output mode, the output compare (oc1x) is cleared on the compare match between tcnt1 and ocr1x while counting up, and set on the compare match while counting down. in inverting compare output mode, the operation is inverted. the dual-slope operation gives a lower maximum operation fre- quency compared to the single-slope operation. howe ver, due to the symmetric feature of the dual-slope pwm modes, these modes are preferred for motor control applications. the main difference between the phase correct, and the phase and frequency correct pwm mode is the time the ocr1x register is up dated by the ocr1x buffer register, (see figure 17- 8 and figure 17-9 ). the pwm resolution for the phase and frequency correct pwm mode can be defined by either icr1 or ocr1a. the minimum resolution allowed is 2-bit (icr1 or ocr1a set to 0x0003), and f ocnxpcpwm f clk_i/o 2 ntop ?? --------------------------- - = 120 2570n?avr?05/11 atmega325/3250/645/6450 the maximum resolution is 16-bit (icr1 or ocr1 a set to max). the pwm resolution in bits can be calculated using the following equation: in phase and frequency correct pwm mode the counter is incremented until the counter value matches either the value in icr1 (wgm13:0 = 8 ), or the value in ocr1a (wgm13:0 = 9). the counter has then reac hed the top and ch anges the count di rection. the tcnt1 value will be equal to top for one timer clock cycle. the timing diagram for the phase correct and frequency correct pwm mode is shown on figure 17-9 . the figure shows phase and frequency correct pwm mode when ocr1a or icr1 is used to define top. the tcnt1 value is in the timing dia- gram shown as a histogram for illustrating the dual-slope operati on. the diagram includes non- inverted and inverted pwm outputs. the small horizontal line marks on the tcnt1 slopes repre- sent compare matches between o cr1x and tcnt1. the oc1x inte rrupt flag will be set when a compare match occurs. figure 17-9. phase and frequency correct pwm mode, timing diagram the timer/counter overflow flag (tov1) is set at the same timer clock cycle as the ocr1x registers are updated with the double buffer value (at bottom). when either ocr1a or icr1 is used for defining the top value, the oc1a or icf1 flag set when tcnt1 has reached top. the interrupt flags can then be used to generate an interrupt each time the counter reaches the top or bottom value. when changing the top value the program must ensure that the new top value is higher or equal to the value of all of the compare registers. if the top value is lower than any of the compare registers, a compare match will neve r occur between the tcnt1 and the ocr1x. as figure 17-9 shows the output generated is, in contrast to the phase correct mode, symmetri- cal in all periods. since the ocr1x registers are updated at bottom, the length of the rising and the falling slopes will always be equal. this gives symmetrical output pulses and is therefore frequency correct. r pfcpwm top 1 + () log 2 () log ---------------------------------- - = ocrnx/top updateand tovn interrupt flag set (interrupt on bottom) ocna interrupt flag set or icfn interrupt flag set (interrupt on top) 1 2 3 4 tcntn period ocnx ocnx (comnx1:0 = 2) (comnx1:0 = 3) 121 2570n?avr?05/11 atmega325/3250/645/6450 using the icr1 register for defining top work s well when using fixed top values. by using icr1, the ocr1a register is free to be used for generating a pwm output on oc1a. however, if the base pwm frequency is actively changed by changing the top value, using the ocr1a as top is clearly a better choice due to its double buffer feature. in phase and frequency correct pwm mode, the compare units allow generation of pwm wave- forms on the oc1x pins. settin g the com1x1:0 bits to two will produce a non-inverted pwm and an inverted pwm output can be generated by setting the com1x1:0 to three (see table 1 on page 124 ). the actual oc1x value will only be visible on the port pin if the data direction for the port pin is set as output (ddr_oc1x). the pwm waveform is generated by setting (or clearing) the oc1x register at the compare match between ocr1x and tcnt1 when the counter incre- ments, and clearing (or setting) the oc1x register at compare match between ocr1x and tcnt1 when the counter decrements. the pw m frequency for the output when using phase and frequency correct pwm can be calculated by the following equation: the n variable represents the prescaler divider (1, 8 , 64, 256, or 1024). the extreme values for the ocr1x register represents special cases when generating a pwm waveform output in the phase correct pwm mode. if the ocr1x is set equal to bottom the output will be continuously low and if set equal to top the output will be set to high for non- inverted pwm mode. for in verted pwm the output will have the opposite lo gic values. if ocr1a is used to define the top va lue (wgm13:0 = 9) and com1a1:0 = 1, the oc1a output will toggle with a 50% duty cycle. 17.10 timer/counte r timing diagrams the timer/counter is a synchronous design and the timer clock (clk t1 ) is therefore shown as a clock enable signal in the following figures. the figures include information on when interrupt flags are set, and when the ocr1x register is updated with the ocr1x buffer value (only for modes utilizing double buffering). figure 17-10 shows a timing diagram for the setting of ocf1x. figure 17-10. timer/counter timing diagram, setting of ocf1x, no prescaling figure 17-11 shows the same timing data, but with the prescaler enabled. f ocnxpfcpwm f clk_i/o 2 ntop ?? --------------------------- - = clk tn (clk i/o /1) ocfnx clk i/o ocrnx tcntn ocrnx value ocrnx - 1 ocrnx ocrnx + 1 ocrnx + 2 122 2570n?avr?05/11 atmega325/3250/645/6450 figure 17-11. timer/counter timing diagram, setting of ocf1x, with prescaler (f clk_i/o / 8 ) figure 17-12 shows the count sequence close to top in various modes. when using phase and frequency correct pwm mode the ocr1x register is updated at bottom. the timing diagrams will be the same, but top should be replaced by bottom, top-1 by bottom+1 and so on. the same renaming applies for modes that set the tov1 flag at bottom. figure 17-12. timer/counter timing diagram, no prescaling figure 17-13 shows the same timing data, but with the prescaler enabled. ocfnx ocrnx tcntn ocrnx value ocrnx - 1 ocrnx ocrnx + 1 ocrnx + 2 clk i/o clk tn (clk i/o /8) tovn (fpwm) and icfn (if used as top) ocrnx (update at top) tcntn (ctc and fpwm) tcntn (pc and pfc pwm) top - 1 top top - 1 top - 2 old ocrnx value new ocrnx value top - 1 top bottom bottom + 1 clk tn (clk i/o /1) clk i/o 123 2570n?avr?05/11 atmega325/3250/645/6450 figure 17-13. timer/counter timing dia gram, with prescaler (f clk_i/o / 8 ) 17.11 register description 17.11.1 tccr1a ? timer/counter1 control register a ? bit 7:6 ? com1a1:0: compare output mode for unit a ? bit 5:4 ? com1b1:0: compare output mode for unit b the com1a1:0 and com1b1:0 control the output compare pins (oc1a and oc1b respec- tively) behavior. if one or both of the com1a1:0 bits are written to one, the oc1a output overrides the normal port functionality of the i/o pin it is connected to. if one or both of the com1b1:0 bit are written to one, the oc1b output overrides the normal port functionality of the i/o pin it is connected to. however, note that the data direction register (ddr) bit correspond- ing to the oc1a or oc1b pin must be set in order to enable the output driver. when the oc1a or oc1b is connected to the pin, the function of the com1x1:0 bits is depen- dent of the wgm13:0 bits setting. table 17-2 shows the com1x1:0 bit functionality when the wgm13:0 bits are set to a normal or a ctc mode (non-pwm). tovn (fpwm) and icf n (if used as top) ocrnx (update at top) tcntn (ctc and fpwm) tcntn (pc and pfc pwm) top - 1 top top - 1 top - 2 old ocrnx value new ocrnx value top - 1 top bottom bottom + 1 clk i/o clk tn (clk i/o /8) bit 7 6 5 4 3210 (0x 8 0) com1a1 com1a0 com1b1 com1b0 ? ? wgm11 wgm10 tccr1a read/write r/w r/w r/w r/w r r r/w r/w initial value 0 0 0 0 0 0 0 0 table 17-2. compare output mode, non-pwm com1a1/com1b1 com1a0/com1b0 description 0 0 normal port operation, oc1a/oc1b disconnected. 0 1 toggle oc1a/oc1b on compare match. 1 0 clear oc1a/oc1b on compare match (set output to low level). 1 1 set oc1a/oc1b on compare match (set output to high level). 124 2570n?avr?05/11 atmega325/3250/645/6450 table 17-3 shows the com1x1:0 bit functionality when the wgm13:0 bits are set to the fast pwm mode. note: 1. a special case occurs when ocr1a/oc r1b equals top and com1a1/com1b1 is set. in this case the compare match is ignored, but the set or clear is done at bottom. see ?fast pwm mode? on page 115. for more details. table 17-4 shows the com1x1:0 bit functionality when the wgm13:0 bits are set to the phase correct or the phase and frequency correct, pwm mode. note: 1. a special case occurs when ocr1a/ ocr1b equals top and com1a1/com1b1 is set. see ?phase correct pwm mode? on page 117. for more details. ? bit 1:0 ? wgm11:0: waveform generation mode combined with the wgm13:2 bits found in the tccr1b register, these bits control the counting sequence of the counter, the source for maximum (top) counter value, and what type of wave- form generation to be used, see table 17-5 . modes of operation supported by the timer/counter unit are: normal mode (counter), clear timer on compare match (ctc) mode, and three types of pulse width modulation (pwm) modes. ( see ?modes of operation? on page 114. ). table 17-3. compare output mode, fast pwm (1) com1a1/com1b1 com1a0/com1b0 description 0 0 normal port operation, oc1a/oc1b disconnected. 0 1 wgm13:0 = 14 or 15: toggle oc1a on compare match, oc1b disconnected (normal port operation). for all other wgm1 settings, normal port operation, oc1a/oc1b disconnected. 1 0 clear oc1a/oc1b on compare match, set oc1a/oc1b at bottom (non-inverting mode). 1 1 set oc1a/oc1b on compare match, clear oc1a/oc1b at bottom (inverting mode). table 17-4. compare output mode, phase correct and phase and frequency correct pwm (1) com1a1/com1b1 com1a0/com1b0 description 0 0 normal port operation, oc1a/oc1b disconnected. 0 1 wgm13:0 = 9 or 11: toggle oc1a on compare match, oc1b disconnected (normal port operation). for all other wgm1 settings, normal port operation, oc1a/oc1b disconnected. 1 0 clear oc1a/oc1b on compare match when up- counting. set oc1a/oc1b on compare match when counting down. 1 1 set oc1a/oc1b on compare match when up- counting. clear oc1a/oc1b on compare match when counting down. 125 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. the ctc1 and pwm11:0 bit defi nition names are obsolete. use the wgm 12:0 definitions. however, the functionality and location of these bits are compatible with previous versions of the timer. 17.11.2 tccr1b ? timer/counter1 control register b ? bit 7 ? icnc1: input capture noise canceler setting this bit (to one) activates the input capt ure noise canceler. when the noise canceler is activated, the input from the input capture pin (icp1) is filtered. the filter function requires four successive equal valued samples of the icp1 pin for changing its output. the input capture is therefore delayed by four oscillator cycles when the noise canceler is enabled. ? bit 6 ? ices1: input capture edge select this bit selects which edge on the input capture pin (icp1) that is used to trigger a capture event. when the ices1 bit is written to zero, a falling (negative) edge is used as trigger, and when the ices1 bit is written to one, a risi ng (positive) edge w ill trigger the capture. when a capture is triggered according to the ices1 setting, the counter value is copied into the input capture register (icr1). the event will also set the input capture flag (icf1), and this can be used to cause an input capture interrupt, if this interrupt is enabled. table 17-5. waveform generation mode bit description (1) mode wgm13 wgm12 (ctc1) wgm11 (pwm11) wgm10 (pwm10) timer/counter mode of operation top update of ocr1 x at tov1 flag set on 0 0 0 0 0 normal 0xffff immediate max 10001pwm, phase correct, 8 -bit 0x00ff top bottom 2 0 0 1 0 pwm, phase correct, 9-bit 0x01ff top bottom 3 0 0 1 1 pwm, phase correct, 10-bit 0x03ff top bottom 4 0 1 0 0 ctc ocr1a immediate max 50101fast pwm, 8 -bit 0x00ff bottom top 6 0 1 1 0 fast pwm, 9-bit 0x01ff bottom top 7 0 1 1 1 fast pwm, 10-bit 0x03ff bottom top 8 1 0 0 0 pwm, phase and frequency correct icr1 bottom bottom 9 1 0 0 1 pwm, phase and frequency correct ocr1a bottom bottom 10 1 0 1 0 pwm, phase correct icr1 top bottom 11 1 0 1 1 pwm, phase correct ocr1a top bottom 12 1 1 0 0 ctc icr1 immediate max 13 1 1 0 1 (reserved) ? ? ? 14 1 1 1 0 fast pwm icr1 bottom top 15 1 1 1 1 fast pwm ocr1a bottom top bit 7654 3210 (0x 8 1) icnc1 ices1 ? wgm13 wgm12 cs12 cs11 cs10 tccr1b read/write r/w r/w r r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 126 2570n?avr?05/11 atmega325/3250/645/6450 when the icr1 is used as top value (see description of the wgm13:0 bits located in the tccr1a and the tccr1b register), the icp1 is disconnected and consequently the input cap- ture function is disabled. ? bit 5 ? reserved bit this bit is reserved for future use. for ensuring compatibility with future de vices, this bit must be written to zero when tccr1b is written. ? bit 4:3 ? wgm13:2: waveform generation mode see tccr1a register description. ? bit 2:0 ? cs12:0: clock select the three clock select bits select the clock source to be used by the timer/counter, see figure 17-10 and figure 17-11 . if external pin modes are used for the timer/counter1, transitions on the t1 pin will clock the counter even if the pin is configured as an output. this feature allows software control of the counting. 17.11.3 tccr1c ? timer/counter1 control register c ? bit 7 ? foc1a: force output compare for unit a ? bit 6 ? foc1b: force output compare for unit b the foc1a/foc1b bits are only active when the wgm13:0 bits specifies a non-pwm mode. however, for ensuring compatibility with future devices, these bits must be set to zero when tccr1a is written when operating in a pwm mode. when writing a logical one to the foc1a/foc1b bit, an immediate compare match is forced on the waveform generation unit. the oc1a/oc1b output is changed according to its com1x1:0 bits setting. note that the foc1a/foc1b bits are implemented as strobes. therefore it is the value present in the com1x1:0 bits that determine the effect of the forced compare. table 17-6. clock select bit description cs12 cs11 cs10 description 0 0 0 no clock source (timer/counter stopped). 001clk i/o /1 (no prescaling) 010clk i/o / 8 (from prescaler) 011clk i/o /64 (from prescaler) 100clk i/o /256 (from prescaler) 101clk i/o /1024 (from prescaler) 1 1 0 external clock source on t1 pin. clock on falling edge. 1 1 1 external clock source on t1 pin. clock on rising edge. bit 7654 3210 (0x 8 2) foc1a foc1b ? ? ? ? ? ? tccr1c read/write r/w r/w r r r r r r initial value 0 0 0 0 0 0 0 0 127 2570n?avr?05/11 atmega325/3250/645/6450 a foc1a/foc1b strobe will not generate any interrupt nor will it clear the timer in clear timer on compare match (ctc) mode using ocr1a as top. the foc1a/foc1b bits are always read as zero. 17.11.4 tcnt1h and tcnt1l ? timer/counter1 the two timer/counter i/o locations (tcnt1h and tcnt1l , combined tcnt1) give direct access, both for read and for write operations, to the timer/counter unit 16-bit counter. to ensure that both the high and low bytes are read and written simultaneously when the cpu accesses these registers, the access is performed using an 8 -bit temporary high byte register (temp). this temporary register is shared by all the other 16-bit registers. see ?accessing 16-bit registers? on page 104. modifying the counter (tcnt1) while the counte r is running introduces a risk of missing a com- pare match between tcnt1 and one of the ocr1x registers. writing to the tcnt1 register blocks (removes) the compare match on the following timer clock for all compare units. 17.11.5 ocr1ah and ocr1al ? ou tput compare register 1 a 17.11.6 ocr1bh and ocr1bl ? ou tput compare register 1 b the output compare registers contain a 16-bit value that is continuously compared with the counter value (tcnt1). a match can be used to generate an output compare interrupt, or to generate a waveform output on the oc1x pin. the output compare registers are 16-bit in size. to ensure that both the high and low bytes are written simultaneously when the cp u writes to these registers, the access is performed using an 8 -bit temporary high byte register (temp). this temporary register is shared by all the other 16-bit registers. see ?accessing 16-bit registers? on page 104. 17.11.7 icr1h and icr1l ? input capture register 1 bit 76543210 (0x 8 5) tcnt1[15:8] tcnt1h (0x 8 4) tcnt1[7:0] tcnt1l read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 (0x 8 9) ocr1a[15:8] ocr1ah (0x 88 ) ocr1a[7:0] ocr1al read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 (0x 8 b) ocr1b[15:8] ocr1bh (0x 8 a) ocr1b[7:0] ocr1bl read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 (0x 8 7) icr1[15:8] icr1h (0x 8 6) icr1[7:0] icr1l read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 128 2570n?avr?05/11 atmega325/3250/645/6450 the input capture is updated with the counter (tcnt1) value each time an event occurs on the icp1 pin (or optionally on the analog comparator output for timer/counter1). the input capture can be used for defining the counter top value. the input capture register is 16-bit in size. to ensure that both the high and low bytes are read simultaneously when the cpu accesses these registers, the access is performed using an 8 -bit temporary high byte register (temp). this temporary register is shared by all the other 16-bit registers. see ?accessing 16-bit registers? on page 104. 17.11.8 timsk1 ? timer/counter 1 interrupt mask register ? bit 5 ? icie1: timer/counter1, input capture interrupt enable when this bit is written to one, and the i-flag in the status register is set (interrupts globally enabled), the timer/counter1 input capture interrupt is enabled. the corresponding interrupt vector ( see ?interrupts? on page 49. ) is executed when the icf1 flag, located in tifr1, is set. ? bit 2 ? ocie1b: timer/counter1, output compare b match interrupt enable when this bit is written to one, and the i-flag in the status register is set (interrupts globally enabled), the timer/counter1 output compare b match interrupt is enabled. the corresponding interrupt vector ( see ?interrupts? on page 49. ) is executed when the ocf1b flag, located in tifr1, is set. ? bit 1 ? ocie1a: timer/counter1, output compare a match interrupt enable when this bit is written to one, and the i-flag in the status register is set (interrupts globally enabled), the timer/counter1 output compare a match interrupt is enabled. the corresponding interrupt vector ( see ?interrupts? on page 49. ) is executed when the ocf1a flag, located in tifr1, is set. ? bit 0 ? toie1: timer/counter1, overflow interrupt enable when this bit is written to one, and the i-flag in the status register is set (interrupts globally enabled), the timer/counter1 overflow interrupt is enabled. the corresponding interrupt vector ( see ?interrupts? on page 49. ) is executed when the tov1 flag, located in tifr1, is set. 17.11.9 tifr1 ? timer/counter1 interrupt flag register ? bit 5 ? icf1: timer/count er1, input capture flag this flag is set when a capture event occurs on the icp1 pin. when the input capture register (icr1) is set by the wgm13:0 to be used as the top value, the icf1 flag is set when the coun- ter reaches the top value. icf1 is automatically cleared when the input capt ure interrupt vector is executed. alternatively, icf1 can be cleared by writing a logic one to its bit location. bit 76543210 (0x6f) ? ?icie1 ? ? ocie1b ocie1a toie1 timsk1 read/write r r r/w r r r/w r/w r/w initial value 0 0 0 0 0 0 0 0 bit 76543210 0x16 (0x36) ? ?icf1 ? ? ocf1b ocf1a tov1 tifr1 read/write r r r/w r r r/w r/w r/w initial value00000000 129 2570n?avr?05/11 atmega325/3250/645/6450 ? bit 2 ? ocf1b: timer/counter1, output compare b match flag this flag is set in the timer clock cycle afte r the counter (tcnt1) value matches the output compare register b (ocr1b). note that a forced output compare (foc 1b) strobe will not set the ocf1b flag. ocf1b is automatically cleared when the output compare match b interrupt vector is exe- cuted. alternatively, ocf1b can be cleared by writing a logic one to its bit location. ? bit 1 ? ocf1a: timer/counter1, output compare a match flag this flag is set in the timer clock cycle afte r the counter (tcnt1) value matches the output compare register a (ocr1a). note that a forced output compare (foc 1a) strobe will not set the ocf1a flag. ocf1a is automatically cleared when the output compare match a interrupt vector is exe- cuted. alternatively, ocf1a can be cleared by writing a logic one to its bit location. ? bit 0 ? tov1: timer/counter1, overflow flag the setting of this flag is dependent of the wgm13:0 bits setting. in normal and ctc modes, the tov1 flag is set when the timer overflows. refer to table 17-5 on page 125 for the tov1 flag behavior when using another wgm13:0 bit setting. tov1 is automatically cleared when the timer/c ounter1 overflow interrupt vector is executed. alternatively, tov1 can be cleared by writing a logic one to its bit location. 130 2570n?avr?05/11 atmega325/3250/645/6450 18. 8-bit timer/counter2 with pwm and asynchronous operation 18.1 features timer/counter2 is a general purpose, single compare unit, 8 -bit timer/counter module. the main features are: ? single compare unit counter ? clear timer on compare match (auto reload) ? glitch-free, phase correct pu lse width modulator (pwm) ? frequency generator ? 10-bit clock prescaler ? overflow and compare match inte rrupt sources (tov2 and ocf2a) ? allows clocking from external 32khz watch crystal independent of the i/o clock 18.2 overview a simplified block diagram of the 8 -bit timer/counter is shown in figure 1 8 -1 . for the actual placement of i/o pins, refer to ?pinout atmega3250/6450? on page 2 . cpu accessible i/o reg- isters, including i/o bits and i/o pins, are shown in bold. the devi ce-specific i/o register and bit locations are listed in the ?register description? on page 143 . figure 18-1. 8 -bit timer/counter block diagram timer/counter data b u s = tcntn waveform generation ocnx = 0 control logic = 0xff top bottom count clear direction tovn (int.req.) ocnx (int.req.) synchronization unit ocrnx tccrnx assrn status flags clk i/o clk asy synchronized status flags asynchronous mode select (asn) tosc1 t/c oscillator tosc2 prescaler clk tn clk i/o 131 2570n?avr?05/11 atmega325/3250/645/6450 18.2.1 registers the timer/counter (tcnt2) and output compare register (ocr2a) are 8 -bit registers. inter- rupt request (shorten as int.req.) signals are al l visible in the timer interrupt flag register (tifr2). all interrupts are individually masked with the timer interrupt mask register (timsk2). tifr2 and timsk2 are not shown in the figure. the timer/counter can be clocked internally, via the prescaler, or asynchronously clocked from the tosc1/2 pins, as detailed later in this section. the asynchronous operation is controlled by the asynchronous status regist er (assr). the clock select lo gic block controls which clock source the timer/counter uses to increment (or de crement) its value. the timer/counter is inac- tive when no clock source is selected. the output from the clock select logic is referred to as the timer clock (clk t2 ). the double buffered output compare register (ocr2a) is compared with the timer/counter value at all times. the result of the compare can be used by the waveform generator to gener- ate a pwm or variable frequency output on the output compare pin (oc2a). see ?output compare unit? on page 132. for details. the compare match event will also set the compare flag (ocf2a) which can be used to generate an output compare interrupt request. 18.2.2 definitions many register and bit references in this document are written in general form. a lower case ?n? replaces the timer/counter number, in this case 2. however, when using the register or bit defines in a program, the precise form must be used, i.e., tcnt2 for accessing timer/counter2 counter value and so on. the definitions in table 1 8 -1 are also used extensively throughout the section. 18.3 timer/counter clock sources the timer/counter can be clocked by an internal synchronous or an external asynchronous clock source. the clock source clk t2 is by default equal to the mcu clock, clk i/o . when the as2 bit in the assr register is written to logic one, the clock source is taken from the timer/counter oscillator connected to tosc1 and tosc2. fo r details on asynchronous operation, see ?assr ? asynchronous status register? on page 145 . for details on clock sour ces and prescaler, see ?timer/counter prescaler? on page 142 . 18.4 counter unit the main part of the 8 -bit timer/counter is the programmable bi-directional counter unit. figure 1 8 -2 shows a block diagram of the counter and its surrounding environment. table 18-1. definitions of timer/counter values. bottom the counter reaches the bottom when it becomes zero (0x00). max the counter reaches its maximum when it becomes 0xff (decimal 255). top the counter reaches the top when it becomes equal to the highest value in the count sequence. the top value can be assigned to be the fixed value 0xff (max) or the value stored in the ocr2a register. the assignment is dependent on the mode of operation. 132 2570n?avr?05/11 atmega325/3250/645/6450 figure 18-2. counter unit block diagram signal description (internal signals): count increment or decrement tcnt2 by 1. direction selects between increment and decrement. clear clear tcnt2 (set all bits to zero). clk t 2 timer/counter clock. top signalizes that tcnt2 has reached maximum value. bottom signalizes that tcnt2 has reached minimum value (zero). depending on the mode of operation used, the counter is cleared, incremented, or decremented at each timer clock (clk t2 ). clk t2 can be generated from an external or internal clock source, selected by the clock select bits (cs22:0). w hen no clock source is selected (cs22:0 = 0) the timer is stopped. however, the tcnt2 value can be accessed by the cpu, regardless of whether clk t2 is present or not. a cpu write overrides (has priority over) all counter clear or count operations. the counting sequence is determined by the setting of the wgm21 and wgm20 bits located in the timer/counter control register (tccr2a). there are close connections between how the counter behaves (counts) and how waveforms are generated on the output compare output oc2a. for more details about advanced count ing sequences and waveform generation, see ?modes of operation? on page 135 . the timer/counter overflow flag (tov2) is set according to the mode of operation selected by the wgm21:0 bits. tov2 can be used for generating a cpu interrupt. 18.5 output compare unit the 8 -bit comparator continuously compares tcnt2 with the output compare register (ocr2a). whenever tcnt2 equals ocr2a, the comparator signals a match. a match will set the output compare flag (ocf2a) at the next timer clock cycle. if enabled (ocie2a = 1), the output compare flag generates an output compare interrupt. the ocf2a flag is automatically cleared when the interrupt is executed. alternat ively, the ocf2a flag can be cleared by soft- ware by writing a logical one to its i/o bit location. the waveform generator uses the match signal to generate an output according to operating mode set by the wgm21:0 bits and com- pare output mode (com2a1:0) bits. the max and bottom signals are used by the waveform generator for handling the special cases of the extreme values in some modes of operation ( ?modes of operation? on page 135 ). figure 1 8 -3 shows a block diagram of the output compare unit. data b u s tcntn control logic count tovn (int.req.) top bottom direction clear tosc1 t/c oscillator tosc2 prescaler clk i/o clk tn 133 2570n?avr?05/11 atmega325/3250/645/6450 figure 18-3. output compare unit, block diagram the ocr2a register is double buffered when us ing any of the pulse width modulation (pwm) modes. for the normal and clear timer on compare (ctc) modes of operation, the double buffering is disabled. the double buffering synchronizes the update of the ocr2a compare register to either top or bottom of the counting sequence. the synchronization prevents the occurrence of odd-length, non-symmetrical pwm pulses, thereby making the output glitch-free. the ocr2a register access may seem complex, but this is not case. when the double buffer- ing is enabled, the cpu has access to the ocr2 a buffer register, and if double buffering is disabled the cpu will access the ocr2a directly. 18.5.1 force output compare in non-pwm waveform generation modes, the match output of the comparator can be forced by writing a one to the fo rce output compare (foc2a) bit. fo rcing compare match will not set the ocf2a flag or reload/clear the ti mer, but the oc2a pin will be updated as if a real compare match had occurred (the com2a1:0 bits settings define whether the oc2a pin is set, cleared or toggled). 18.5.2 compare match bloc king by tcnt2 write all cpu write operations to the tcnt2 register will block any compare matc h that occurs in the next timer clock cycle, even when the timer is stopped. this feature allo ws ocr2a to be initial- ized to the same value as tcnt2 without triggering an interrupt when the timer/counter clock is enabled. 18.5.3 using the output compare unit since writing tcnt2 in any mode of operation will block all comp are matches for one timer clock cycle, there are risks involved when changing tcnt2 when using the output compare unit, independently of whether the timer/counter is running or not. if the value written to tcnt2 equals the ocr2a value, the compare match will be missed, resulting in incorrect waveform generation. similarly, do not write the tcnt2 value equal to bottom when the counter is counting down. ocfn x (int.req.) = (8-bit comparator ) ocrnx ocnx data b u s tcntn wgmn1:0 waveform generator top focn comnx1:0 bottom 134 2570n?avr?05/11 atmega325/3250/645/6450 the setup of the oc2a should be performed before setting the data direction register for the port pin to output. the easiest way of setting the oc2a value is to use the force output com- pare (foc2a) strobe bit in normal mode. the oc2a register keeps its value even when changing between waveform generation modes. be aware that the com2a1:0 bits are not double buffered together with the compare value. changing the com2a1:0 bits will take effect immediately. 18.6 compare match output unit the compare output mode (com2a1:0) bits have two functions. the waveform generator uses the com2a1:0 bits for defining the output compare (oc2a) state at the next compare match. also, the com2a1:0 bits control the oc2a pin output source. figure 1 8 -4 shows a sim- plified schematic of the logic affected by the com2a1:0 bit setting. the i/o registers, i/o bits, and i/o pins in the figure are shown in bold. only the parts of the general i/o port control regis- ters (ddr and port) that are affected by the com2a1:0 bits are shown. when referring to the oc2a state, the reference is for the internal oc2a register, not the oc2a pin. figure 18-4. compare match output unit, schematic the general i/o port function is overridden by the output compare (oc2a) from the waveform generator if either of the com2a1:0 bits are set. however, the oc2a pin direction (input or out- put) is still controlled by the da ta direction register (ddr) for th e port pin. the data direction register bit for the oc2a pin (ddr_oc2a) must be set as output before the oc2a value is vis- ible on the pin. the port override function is independent of the waveform generation mode. the design of the output compare pin logic allows initialization of the oc2a state before the output is enabled. note that some com2a1:0 bit settings are reserved for certain modes of operation. see ?register description? on page 143. port ddr dq dq ocnx pin ocnx dq waveform generator comnx1 comnx0 0 1 data b u s focnx clk i/o 135 2570n?avr?05/11 atmega325/3250/645/6450 18.6.1 compare output mode and waveform generation the waveform generator uses the com2a1:0 bits differently in normal, ctc, and pwm modes. for all modes, setting the com2a1:0 = 0 tells the waveform generator that no action on the oc2a register is to be performed on the next compare match. for compare output actions in the non-pwm modes refer to table 1 8 -3 on page 144 . for fast pwm mode, refer to table 1 8 -4 on page 144 , and for phase correct pwm refer to table 1 8 -5 on page 144 . a change of the com2a1:0 bits st ate will have effect at the first compare match after the bits are written. for non-pwm modes, the action can be fo rced to have immediate effect by using the foc2a strobe bits. 18.7 modes of operation the mode of operation, i.e., the behavior of the timer/counter and the output compare pins, is defined by the combination of the waveform generation mode (wgm21:0) and compare output mode (com2a1:0) bits. the compare output mode bits do not affect the counting sequence, while the waveform generation mode bits do. the com2a1:0 bits control whether the pwm output generated should be inverted or not (inverted or non-inverted pwm). for non-pwm modes the com2a1:0 bits control whether the output should be set, cleared, or toggled at a compare match ( see ?compare match output unit? on page 134. ). for detailed timing information refer to ?timer/counter timing diagrams? on page 139 . 18.7.1 normal mode the simplest mode of operation is the normal mode (wgm21:0 = 0). in this mode the counting direction is always up (incrementing), and no counter clear is performed. the counter simply overruns when it passes its maximum 8 -bit value (top = 0xff) and then restarts from the bot- tom (0x00). in normal o peration the timer/counter overflow flag (tov2) will be set in the same timer clock cycle as the tcnt2 becomes zero. the tov2 flag in this case behaves like a ninth bit, except that it is only set, not cleared. however, combined with the timer overflow interrupt that automatically clears the tov2 flag, the timer resolution can be increased by software. there are no special cases to consider in the normal mode, a new counter value can be written anytime. the output compare unit can be used to generate interrupts at some given time. using the out- put compare to generate waveforms in normal mode is not recommended, since this will occupy too much of the cpu time. 18.7.2 clear timer on compare match (ctc) mode in clear timer on compare or ctc mode (wgm 21:0 = 2), the ocr2a register is used to manipulate the counter resolution. in ctc mode the counter is cleared to zero when the counter value (tcnt2) matches the ocr2a. the ocr2a defines the top value for the counter, hence also its resolution. this mode allows greater control of the compare match output frequency. it also simplifies the operation of counting external events. the timing diagram for the ctc mode is shown in figure 1 8 -5 . the counter value (tcnt2) increases until a compare match occurs between tcnt2 and ocr2a, and then counter (tcnt2) is cleared. 136 2570n?avr?05/11 atmega325/3250/645/6450 figure 18-5. ctc mode, timing diagram an interrupt can be generated each time the counter value reaches the top value by using the ocf2a flag. if the interrupt is enabled, the interrupt handler routine can be used for updating the top value. however, changing the top to a value close to bottom when the counter is running with none or a low prescaler value must be done with care since the ctc mode does not have the double buffering feature. if the new value written to ocr2a is lower than the cur- rent value of tcnt2, the c ounter will miss the compare matc h. the counter will then have to count to its maximum value (0xff) and wrap around starting at 0x00 before the compare match can occur. for generating a waveform output in ctc mode, the oc2a output can be set to toggle its logical level on each compare match by setting the compare output mode bits to toggle mode (com2a1:0 = 1). the oc2a value will not be visible on the port pin unless the data direction for the pin is set to output. the wavefo rm generated will have a maximum frequency of f oc2a = f clk_i/o /2 when ocr2a is set to zero (0x00). the waveform frequency is defined by the following equation: the n variable represents the prescale factor (1, 8 , 32, 64, 12 8 , 256, or 1024). as for the normal mode of operation, the tov2 flag is set in the same timer clock cycle that the counter counts from max to 0x00. 18.7.3 fast pwm mode the fast pulse width modulation or fast pwm mode (wgm21:0 = 3) provides a high frequency pwm waveform generation option. the fast pwm di ffers from the other pwm option by its sin- gle-slope operation. the counter counts from bottom to max then restarts from bottom. in non-inverting compare output mode, the output compare (oc2a) is cleared on the compare match between tcnt2 and ocr2a, and set at bottom. in inverting compare output mode, the output is set on compare match and cleared at bottom. due to the single-slope operation, the operating frequency of the fast pwm mode can be twice as high as the phase correct pwm mode that uses dual-slope operation. this high frequency makes the fast pwm mode well suited for power regulation, rectification, and dac app lications. high frequency a llows physically small sized external components (coils, capacitors), and therefore reduces total system cost. in fast pwm mode, the counter is incremented until the counter value matches the max value. the counter is then cleared at the following timer clock cycle. the timing diagram for the fast tcntn ocnx (toggle) ocnx interrupt flag set 1 4 period 2 3 (comnx1:0 = 1) f ocnx f clk_i/o 2 n 1 ocrnx + () ?? ------------------------------------------------- - = 137 2570n?avr?05/11 atmega325/3250/645/6450 pwm mode is shown in figure 1 8 -6 . the tcnt2 value is in the timing diagram shown as a his- togram for illustrating the single-slope operation. the diagram includes non-inverted and inverted pwm outputs. the small horizontal line marks on the tcnt2 slopes represent compare matches between ocr2a and tcnt2. figure 18-6. fast pwm mode, timing diagram the timer/counter overflow flag (tov2) is set each time the counter reaches max. if the inter- rupt is enabled, the interrupt handler routine can be used for updating the compare value. in fast pwm mode, the compare unit allows generation of pwm waveforms on the oc2a pin. setting the com2a1:0 bits to two will produce a non-inverted pwm and an inverted pwm output can be generated by setting the com2a1:0 to three (see table 1 8 -4 on page 144 ). the actual oc2a value will only be visible on the port pin if the data direction for the port pin is set as out- put. the pwm waveform is generated by setting (or clearing) the oc2a register at the compare match between ocr2a and tcnt2, and clearing (or setting) the oc2a register at the timer clock cycle the counter is cleared (changes from max to bottom). the pwm frequency for the output can be calculated by the following equation: the n variable represents the prescale factor (1, 8 , 32, 64, 12 8 , 256, or 1024). the extreme values for the ocr2a register represent special cases when generating a pwm waveform output in the fast pwm mode. if the ocr2a is set equal to bottom, the output will be a narrow spike for each max+1 timer clock cycle. setting the ocr2a equal to max will result in a constantly high or low output (depending on the polarity of the output set by the com2a1:0 bits.) a frequency (with 50% duty cycle) waveform output in fast pwm mode can be achieved by set- ting oc2a to toggle its logical level on each compare match (com2a1:0 = 1). the waveform generated will have a ma ximum frequency of f oc2 = f clk_i/o /2 when ocr2a is set to zero. this fea- ture is similar to the oc2a toggle in ctc mode, except the double buffer feature of the output compare unit is enabled in the fast pwm mode. tcntn ocrnx update and tovn interrupt flag set 1 period 2 3 ocnx ocnx (comnx1:0 = 2) (comnx1:0 = 3) ocrnx interrupt flag set 4 5 6 7 f ocnxpwm f clk_i/o n 256 ? ------------------ = 138 2570n?avr?05/11 atmega325/3250/645/6450 18.7.4 phase correct pwm mode the phase correct pwm mode (wgm21:0 = 1) pr ovides a high resolution phase correct pwm waveform generation option. the phase correct pwm mode is based on a dual-slope operation. the counter counts repeatedly from bottom to max and then from max to bottom. in non- inverting compare output mode, the output compare (oc2a) is cleared on the compare match between tcnt2 and ocr2a while counting up, and set on the compare match while counting down. in inverting output compare mode, the operation is inverted. the dual-slope operation has lower maximum operation frequency than single slope operation. however, due to the sym- metric feature of the dual-slope pwm modes, these modes are preferred for motor control applications. the pwm resolution for the phase correct pwm m ode is fixed to eight bits. in phase correct pwm mode the counter is incremented until the counter value matches max. when the counter reaches max, it changes the count direction. the tcnt2 value will be equal to max for one timer clock cycle. the timing diagram for the phase correct pwm mode is shown on figure 1 8 -7 . the tcnt2 value is in the timing diagram shown as a histogram for illustrating the dual-slope operation. the diagram includes non-inverted and inverted pwm outputs. the small horizontal line marks on the tcnt2 slopes represent compare matches between ocr2a and tcnt2. figure 18-7. phase correct pwm mode, timing diagram the timer/counter overflow flag (tov2) is set each time the counter reaches bottom. the interrupt flag can be used to generate an interrupt each time the counter reaches the bottom value. in phase correct pwm mode, the compare unit allows generation of pwm waveforms on the oc2a pin. setting the com2a1:0 bits to two will produce a non-inverted pwm. an inverted pwm output can be generated by setting the com2a1:0 to three (see table 1 8 -5 on page 144 ). the actual oc2a value will only be visible on the port pin if the data direction for the port pin is set as output. the pwm waveform is generated by clearing (or setting) the oc2a register at the compare match between ocr2a and tcnt2 when the counter increments, and setting (or clearing) the oc2a register at compare match between ocr2a and tcnt2 when the counter tovn interrupt flag set ocnx interrupt flag set 1 2 3 tcntn period ocnx ocnx (comnx1:0 = 2) (comnx1:0 = 3) ocrnx update 139 2570n?avr?05/11 atmega325/3250/645/6450 decrements. the pwm frequency for the output when using phase correct pwm can be calcu- lated by the following equation: the n variable represents the prescale factor (1, 8 , 32, 64, 12 8 , 256, or 1024). the extreme values for the ocr2a register represent special cases when generating a pwm waveform output in the phase correct pwm mode. if the ocr2a is set equal to bottom, the output will be continuously low an d if set equal to max the output will be continuously high for non-inverted pwm mode. for in verted pwm the output will have the opposite logic values. at the very start of period 2 in figure 1 8 -7 ocn has a transition from high to low even though there is no compare match. the point of this transition is to guarantee symmetry around bot- tom. there are two cases that give a transition without compare match. ? ocr2a changes its valu e from max, like in figure 1 8 -7 . when the ocr2a value is max the ocn pin value is the same as the result of a down-counting compare match. to ensure symmetry around bottom the ocn value at max must correspond to the result of an up- counting compare match. ? the timer starts counting from a value higher than the one in ocr2a, and for that reason misses the compare match and hence the ocn change that would have happened on the way up. 18.8 timer/counter timing diagrams the following figures show the timer/counter in synchronous mode, and the timer clock (clk t2 ) is therefore shown as a clock enable signal. in asynchronous mode, clk i/o should be replaced by the timer/counter oscillator clock. the figures include information on when interrupt flags are set. figure 2 contains timing data for basic timer/counter operation. the figure shows the count sequence close to the max value in all modes other than phase correct pwm mode. figure 2. timer/counter timing diagram, no prescaling figure 1 8 - 8 shows the same timing data, but with the prescaler enabled. f ocnxpcpwm f clk_i/o n 510 ? ------------------ = clk tn (clk i/o /1) tovn clk i/o tcntn max - 1 max bottom bottom + 1 140 2570n?avr?05/11 atmega325/3250/645/6450 figure 18-8. timer/counter timing dia gram, with prescaler (f clk_i/o / 8 ) figure 1 8 -9 shows the setting of ocf2a in all modes except ctc mode. figure 18-9. timer/counter timing diagram, setting of ocf2a, with prescaler (f clk_i/o / 8 ) figure 1 8 -10 shows the setting of ocf2a and the clearing of tcnt2 in ctc mode. figure 18-10. timer/counter timing diagram, clear timer on compare match mode, with pres- caler (f clk_i/o / 8 ) tovn tcntn max - 1 max bottom bottom + 1 clk i/o clk tn (clk i/o /8) ocfnx ocrnx tcntn ocrnx value ocrnx - 1 ocrnx ocrnx + 1 ocrnx + 2 clk i/o clk tn (clk i/o /8) ocfnx ocrnx tcntn (ctc) top top - 1 top bottom bottom + 1 clk i/o clk tn (clk i/o /8) 141 2570n?avr?05/11 atmega325/3250/645/6450 18.9 asynchronous operati on of timer/counter2 when timer/counter2 operates asynchronously, some considerations must be taken. ? warning: when switching between asynchronous and synchronous clocking of timer/counter2, the timer registers tcnt2, ocr2a, and tccr2a might be corrupted. a safe procedure for switching clock source is: 1. disable the timer/counter2 interrupts by clearing ocie2a and toie2. 2. select clock source by setting as2 as appropriate. 3. write new values to tcnt2, ocr2a, and tccr2a. 4. to switch to asynchronous operation: wait for tcn2ub, ocr2ub, and tcr2ub. 5. clear the timer/counter2 interrupt flags. 6. enable interrupts, if needed. ? the cpu main clock frequenc y must be more than four times the oscillator frequency. ? when writing to one of the regi sters tcnt2, ocr2a, or tccr2a, the value is transferred to a temporary register, and latched after two positive edges on tosc1. the user should not write a new value before the contents of the temporary register have been transferred to its destination. each of the three mentioned registers have their individual temporary register, which means that e.g. writing to tcnt2 does not disturb an ocr2a write in progress. to detect that a transfer to the destination regist er has taken place, the asynchronous status register ? assr ha s been implemented. ? when entering power-save or adc noise reduction mode after having written to tcnt2, ocr2a, or tccr2a, the user must wait until the written register has been updated if timer/counter2 is used to wake up the device. other wise, the mcu will enter sleep mode before the changes are effective. this is particularly important if the output compare2 interrupt is used to wake up the device, since the output compare function is disabled during writing to ocr2a or tcnt2. if the write cycle is not finished, and the mcu enters sleep mode before the ocr2ub bit returns to zero, the device will never receive a compare match interrupt, and the mcu will not wake up. ? if timer/counter2 is used to wake the device up from power-save or adc noise reduction mode, precautions must be taken if the user wants to re-enter one of these modes: the interrupt logic needs one tosc1 cycle to be reset. if the time between wake-up and re- entering sleep mode is less than one tosc1 cycle, the interrupt will not occur, and the device will fail to wake up. if the user is in doubt whether the time be fore re-entering power- save or adc noise reduction mode is suffic ient, the following algorithm can be used to ensure that one tosc1 cycle has elapsed: 1. write a value to tccr2a, tcnt2, or ocr2a. 2. wait until the corresponding update busy flag in assr returns to zero. 3. enter power-save or adc noise reduction mode. ? when the asynchronous operation is selected, the 32.76 8 khz oscillator for timer/counter2 is always running, except in power-down and standby modes. after a power-up reset or wake-up from power-down or standby mode, the user should be aware of the fact that this oscillator might take as long as one second to stabilize. the us er is advised to wait for at least one second before using timer/counter2 after power-up or wake-up from power-down or standby mode. the contents of all timer/counter2 registers must be considered lost after a wake-up from power-down or standby mode due to unstable clock signal upon start- up, no matter whether the oscillator is in use or a clock signal is applied to the tosc1 pin. ? description of wake up from power-save or adc noise reduction mode when the timer is clocked asynchronously: when the interrupt condit ion is met, the wake up process is started on the following cycle of the timer clock, that is, the timer is always advanced by at least one before the processor can read the counter value. after wake-up, the mcu is halted for four 142 2570n?avr?05/11 atmega325/3250/645/6450 cycles, it executes the interrupt routine, and resumes execution from the instruction following sleep. ? reading of the tcnt2 register shortly after wake-up from power-save may give an incorrect result. since tcnt2 is clocked on the asynchronous tosc clock, reading tcnt2 must be done through a register synchronized to the internal i/o clock domain. synchronization takes place for every rising tosc1 edge. when waking up from power- save mode, and the i/o clock (clk i/o ) again becomes active, tcnt2 will read as the previous value (before entering sleep) until the next rising tosc1 edge. the phase of the tosc clock after waking up from power-save mode is essentially unpredictable, as it depends on the wake-up time. the recommended procedure for reading tcnt2 is thus as follows: 1. write any value to either of the registers ocr2a or tccr2a. 2. wait for the corresponding update busy flag to be cleared. 3. read tcnt2. ? during asynchronous operation, the synchronization of the interrupt flags for the asynchronous timer takes 3 processor cycles plus one timer cycle. t he timer is therefore advanced by at least one before the processo r can read the timer value causing the setting of the interrupt flag. the output compare pi n is changed on the timer clock and is not synchronized to the processor clock. 18.10 timer/counter prescaler figure 18-11. prescaler for timer/counter2 the clock source for timer/counter2 is named clk t2s . clk t2s is by default connected to the main system i/o clock clk i o . by setting the as2 bit in assr, timer/counter2 is asynchronously clocked from the tosc1 pin. this enables us e of timer/counter2 as a real time counter (rtc). when as2 is set, pins tosc1 and tosc 2 are disconnected from port c. a crystal can then be connected between the tosc1 and tosc2 pins to serve as an independent clock source for timer/counter2 . the oscillator is optimiz ed for use with a 32.76 8 khz crystal. if apply- ing an external clock on tosc1, the exclk bit in assr must be set. 10-bit t/c prescaler timer/counter2 clock source clk i/o clk t2s tosc1 as2 cs20 cs21 cs22 clk t2s /8 clk t2s /64 clk t2s /128 clk t2s /1024 clk t2s /256 clk t2s /32 0 psr2 clear clk t2 143 2570n?avr?05/11 atmega325/3250/645/6450 for timer/counter2, the possible prescaled selections are: clk t2s / 8 , clk t2s /32, clk t2s /64, clk t2s /12 8 , clk t2s /256, and clk t2s /1024. additionally, clk t2s as well as 0 (stop) may be selected. setting the psr2 bit in gtccr resets the prescaler. this allows the user to operate with a pre- dictable prescaler. 18.11 register description 18.11.1 tccr2a ? timer/counter control register a ? bit 7 ? foc2a: force output compare a the foc2a bit is only active when the wgm bits specify a non-pwm mode. however, for ensur- ing compatibility with future devices, this bit mu st be set to zero when tccr2a is written when operating in pwm mode. when writing a logical one to the foc2a bit, an immediate compare match is forced on the waveform generation unit. the oc2a output is changed according to its com2a1:0 bits setting. note that the foc2a bit is implemented as a strobe. therefore it is the value present in the com2a1:0 bits that determines the effect of the forced compare. a foc2a strobe will not gen erate any interrupt, nor will it cl ear the timer in ctc mode using ocr2a as top. the foc2a bit is always read as zero. ? bit 6, 3 ? wgm21:0: waveform generation mode these bits control the counting sequence of the counter, the source for the maximum (top) counter value, and what type of waveform generation to be used. modes of operation supported by the timer/counter unit are: normal mode, clear timer on compare match (ctc) mode, and two types of pulse width modulation (pwm) modes. see table 1 8 -2 and ?modes of operation? on page 135 . note: 1. the ctc2 and pwm2 bit definition names are now obsolete. use t he wgm21:0 definitions. however, the functionality and location of these bits are compatible with previous versions of the timer. bit 7 6 5 4 3 2 1 0 (0xb0) foc2a wgm20 com2a1 com2a0 wgm21 cs22 cs21 cs20 tccr2a read/write w r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 table 18-2. waveform generation mode bit description (1) mode wgm21 (ctc2) wgm20 (pwm2) timer/counter mode of operation top update of ocr2a at tov2 flag set on 0 0 0 normal 0xff immediate max 1 0 1 pwm, phase correct 0xff top bottom 2 1 0 ctc ocr2a immediate max 31 1fast pwm 0xffbottommax 144 2570n?avr?05/11 atmega325/3250/645/6450 ? bit 5:4 ? com2a1:0: compare match output mode a these bits control the output compare pin (oc2a) behavior. if one or both of the com2a1:0 bits are set, the oc2a output overrides the normal po rt functionality of the i/o pin it is connected to. however, note that the data direction register (ddr) bit corresponding to oc2a pin must be set in order to enable the output driver. when oc2a is connected to the pin, the function of the com2a1:0 bits depends on the wgm21:0 bit setting. table 1 8 -3 shows the com2a1:0 bit functionality when the wgm21:0 bits are set to a normal or ctc mode (non-pwm). table 1 8 -4 shows the com2a1:0 bit functionality when the wgm21:0 bits are set to fast pwm mode. note: 1. a special case occurs when ocr2a equals top and com2a1 is set. in this case, the com- pare match is ignored, but the set or clear is done at bottom. see ?fast pwm mode? on page 136 for more details. table 1 8 -5 shows the com21:0 bit functionality when the wgm21:0 bits are set to phase cor- rect pwm mode. note: 1. a special case occurs when ocr2a equals top and com2a1 is set. in this case, the com- pare match is ignored, but the set or clear is done at top. see ?phase correct pwm mode? on page 13 8 for more details. table 18-3. compare output mode, non-pwm mode com2a1 com2a0 description 0 0 normal port operation, oc2a disconnected. 0 1 toggle oc2a on compare match. 1 0 clear oc2a on compare match. 1 1 set oc2a on compare match. table 18-4. compare output mode, fast pwm mode (1) com2a1 com2a0 description 0 0 normal port operation, oc2a disconnected. 01reserved 1 0 clear oc2a on compare match, set oc2a at bottom, (non-inverting mode). 1 1 set oc2a on compare match, clear oc2a at bottom, (inverting mode). table 18-5. compare output mode, phase correct pwm mode (1) com2a1 com2a0 description 0 0 normal port operation, oc2a disconnected. 01reserved 1 0 clear oc2a on compare match when up-counting. set oc2a on compare match when counting down. 1 1 set oc2a on compare match when up-counting. clear oc2a on compare match when counting down. 145 2570n?avr?05/11 atmega325/3250/645/6450 ? bit 2:0 ? cs22:0: clock select the three clock select bits select the clock source to be used by the timer/counter, see table 1 8 -6 . 18.11.2 tcnt2 ? timer/counter register the timer/counter register gives direct ac cess, both for read and write operations, to the timer/counter unit 8 -bit counter. writing to the tcnt2 register blocks (removes) the compare match on the following timer clock. modifying the counter (tcnt2) while the counter is running, introduces a risk of missing a compare match between tcnt2 and the ocr2a register. 18.11.3 ocr2a ? output compare register a the output compare register a contains an 8 -bit value that is continuously compared with the counter value (tcnt2). a match can be used to generate an output compare interrupt, or to generate a waveform output on the oc2a pin. 18.11.4 assr ? asynchronous status register ? bit 4 ? exclk: enable external clock input when exclk is written to one, and asynchronous clock is selected, the external clock input buf- fer is enabled and an external cl ock can be input on timer oscilla tor 1 (tosc1) pin instead of a 32khz crystal. writing to exclk should be done before asynchronous operation is selected. note that the crystal oscillator will only run when this bit is zero. table 18-6. clock select bit description cs22 cs21 cs20 description 0 0 0 no clock source (timer/counter stopped). 001clk t2s /(no prescaling) 010clk t2s / 8 (from prescaler) 011clk t2s /32 (from prescaler) 100clk t2s /64 (from prescaler) 101clk t2s /12 8 (from prescaler) 110clk t 2 s /256 (from prescaler) 111clk t 2 s /1024 (from prescaler) bit 76543210 (0xb2) tcnt2[7:0] tcnt2 read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 76543210 (0xb3) ocr2a[7:0] ocr2a read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 bit 765 4 3 2 1 0 (0xb6) ? ? ? exclk as2 tcn2ub ocr2ub tcr2ub assr read/write r r r r/w r/w r r r initial value 0 0 0 0 0 0 0 0 146 2570n?avr?05/11 atmega325/3250/645/6450 ? bit 3 ? as2: asynchronous timer/counter2 when as2 is written to zero, timer/counter2 is clocked from the i/o clock, clk i/o . when as2 is written to one, timer/counter2 is clocked from a crystal oscilla tor connected to the timer oscil- lator 1 (tosc1) pin. when the value of as2 is changed, the contents of tcnt2, ocr2a, and tccr2a might be corrupted. ? bit 2 ? tcn2ub: timer/counter2 update busy when timer/counter2 operates asynchronously and tcnt2 is written, this bit becomes set. when tcnt2 has been updated from the temporary storage register, this bit is cleared by hard- ware. a logical zero in this bit indicates that tcnt2 is ready to be updated with a new value. ? bit 1 ? ocr2ub: output co mpare register2 update busy when timer/counter2 operates asynchronously and ocr2a is written, this bit becomes set. when ocr2a has been updated from the temporary storage register, this bit is cleared by hard- ware. a logical zero in this bit indicates that ocr2a is ready to be updated with a new value. ? bit 0 ? tcr2ub: timer/counter control register2 update busy when timer/counter2 operates asynchronously and tccr2a is written, this bit becomes set. when tccr2a has been updated from the tempor ary storage register, this bit is cleared by hardware. a logical zero in this bit indicates that tccr2a is ready to be updated with a new value. if a write is performed to any of the three timer/counter2 registers while its update busy flag is set, the updated value might get corrupted and cause an unintentional interrupt to occur. the mechanisms for reading tcnt2, ocr2a, and tccr2a are different. when reading tcnt2, the actual timer value is read. when reading ocr2a or tccr2a, the value in the tem- porary storage register is read. 18.11.5 timsk2 ? timer/counter2 interrupt mask register ? bit 1 ? ocie2a: timer/counter2 output compare match a interrupt enable when the ocie2a bit is written to one and the i-bit in the status register is set (one), the timer/counter2 compare match a interrupt is enabled. the corresponding interrupt is executed if a compare match in timer/coun ter2 occurs, i.e., when the ocf2a bit is set in the timer/coun- ter 2 interrupt flag register ? tifr2. ? bit 0 ? toie2: timer/counter2 overflow interrupt enable when the toie2 bit is written to one and the i-bit in the status register is set (one), the timer/counter2 overflow interrupt is enabled. the corresponding interrupt is executed if an overflow in timer/counter2 occurs, i.e., when the tov2 bit is set in the timer/counter2 interrupt flag register ? tifr2. bit 76543210 (0x70) ? ? ? ? ? ? ocie2a toie2 timsk2 read/writerrrrrrr/wr/w initial value 0 0 0 0 0 0 0 0 147 2570n?avr?05/11 atmega325/3250/645/6450 18.11.6 tifr2 ? timer/counter2 interrupt flag register ? bit 1 ? ocf2a: output compare flag 2 a the ocf2a bit is set (one) when a compare match occurs between the timer/counter2 and the data in ocr2a ? output compare register2. ocf2a is cleared by hardware when executing the corresponding interrupt handling vector. alter natively, ocf2a is cleared by writing a logic one to the flag. when the i-bit in sreg, ocie2a (timer/counter2 compare match interrupt enable), and ocf2a are set (one), the timer/counter2 compare match interrupt is executed. ? bit 0 ? tov2: timer/counter2 overflow flag the tov2 bit is set (one) when an overflow occu rs in timer/counter2. tov2 is cleared by hard- ware when executing the corresponding interrupt handling vector. alternatively, tov2 is cleared by writing a logic one to the flag. when the sreg i-bit, toie2a (timer/counter2 overflow inter- rupt enable), and tov2 are set (one), the timer/ counter2 overflow interrupt is executed. in pwm mode, this bit is set when timer/coun ter2 changes counting direction at 0x00. 18.11.7 gtccr ? general time r/counter control register ? bit 1 ? psr2: prescaler reset timer/counter2 when this bit is one, the time r/counter2 prescaler will be rese t. this bit is normally cleared immediately by hardware. if the bit is written wh en timer/counter2 is operating in asynchronous mode, the bit will remain one until the presca ler has been reset. the bit will not be cleared by hardware if the tsm bit is set. refer to the description of the ?bit 7 ? tsm: timer/counter syn- chronization mode? on page 101 for a description of the timer/counter synchronization mode. bit 76543210 0x17 (0x37) ? ? ? ? ? ? ocf2a tov2 tifr2 read/writerrrrrrr/wr/w initial value00000000 bit 7 6 5 4 3 2 1 0 0x23 (0x43) tsm ? ? ? ? ? psr2 psr10 gtccr read/write r/w r r r r r r/w r/w initial value 0 0 0 0 0 0 0 0 148 2570n?avr?05/11 atmega325/3250/645/6450 19. spi ? serial peripheral interface 19.1 features the atmel atmega325/3250/645/6450 spi includes the following features: ? full-duplex, three-wire synchronous data transfer ? master or slave operation ? lsb first or msb first data transfer ? seven programmable bit rates ? end of transmission interrupt flag ? write collision flag protection ? wake-up from idle mode ? double speed (ck/2) master spi mode 19.2 overview the serial peripheral interface (spi) allows hi gh-speed synchronous data transfer between the atmel atmega325/3250/645/6450 and peripheral devices or between several avr devices. the prspi bit in ?power reduction register? on page 37 must be written to zero to enable the spi module. figure 19-1. spi block diagram (1) note: 1. refer to figure 1-1 on page 2 , and table 14-3 on page 6 8 for spi pin placement. spi2x spi2x divider /2/4/8/16/32/64/128 149 2570n?avr?05/11 atmega325/3250/645/6450 the interconnection between master and slave cpus with spi is shown in figure 19-2 . the sys- tem consists of two shift registers, and a master clock generator. the spi master initiates the communication cycle when pu lling low the slave select ss pin of the desired slave. master and slave prepare the data to be sent in their respective shift registers, and the master generates the required clock pulses on the sck line to interchange data. data is always shifted from mas- ter to slave on the master out ? slave in, mosi, line, and from slave to master on the master in ? slave out, miso, line. after ea ch data packet, the master will synchronize the slave by pulling high the slave select, ss , line. when configured as a master, the spi interface has no automatic control of the ss line. this must be handled by user software before communication can start. when this is done, writing a byte to the spi data register starts the spi clock generator, and the hardware shifts the eight bits into the slave. after shifting one byte , the spi clock generator stops, setting the end of transmission flag (spif). if the spi interrupt enable bit (spie) in the spcr register is set, an interrupt is requested. the master may continue to shift the next byte by writing it into spdr, or signal the end of packet by pulling high the slave select, ss line. the last incoming byte will be kept in the buffer register for later use. when configured as a slave, the spi interface will remain sleeping with miso tri-stated as long as the ss pin is driven high. in this state, software may update the contents of the spi data register, spdr, but the data will not be shifted out by incoming clock pulses on the sck pin until the ss pin is driven low. as one byte has been completely shifted, the end of transmission flag, spif is set. if the spi interrupt enable bit, spie, in the spcr register is set, an interrupt is requested. the slave may continue to place new data to be sent into spdr before reading the incoming data. the last incoming byte will be kept in the buffer register for later use. figure 19-2. spi master-slave interconnection the system is single buffered in the transmit di rection and double buffered in the receive direc- tion. this means that bytes to be transmitted cannot be written to the spi data register before the entire shift cycle is complet ed. when receiving data, however, a received character must be read from the spi data register before the next character has been completely shifted in. oth- erwise, the first byte is lost. in spi slave mode, the control logic will sample the incoming signal of the sck pin. to ensure correct sampling of the clock signal, the minimum low and high period should be: low period: longer than 2 cpu clock cycles. high period: longer than 2 cpu clock cycles. shift enable 150 2570n?avr?05/11 atmega325/3250/645/6450 when the spi is enabled, the data direction of the mosi, miso, sck, and ss pins is overridden according to table 19-1 . for more details on automatic port overrides, refer to ?alternate port functions? on page 66 . note: 1. see ?alternate functions of port b? on page 6 8 for a detailed description of how to define the direction of the user defined spi pins. table 19-1. spi pin overrides (1) pin direction, master spi direction, slave spi mosi user defined input miso input user defined sck user defined input ss user defined input 151 2570n?avr?05/11 atmega325/3250/645/6450 the following code examples show how to initialize the spi as a master and how to perform a simple transmission. ddr_spi in the examples mu st be replaced by the actual data direction register controlling the spi pins. dd_mosi, dd_miso and dd_sck must be replaced by the actual data direction bits for these pins. e.g. if mosi is placed on pin pb5, replace dd_mosi with ddb5 and ddr_spi with ddrb. note: 1. see ?about code examples? on page 9 . assembly code example (1) spi_masterinit: ; set mosi and sck output, all others input ldi r17,(1< 154 2570n?avr?05/11 atmega325/3250/645/6450 figure 19-3. spi transfer format with cpha = 0 figure 19-4. spi transfer format with cpha = 1 19.5 register description 19.5.1 spcr ? spi control register ? bit 7 ? spie: spi interrupt enable this bit causes the spi in terrupt to be executed if spif bit in the spsr register is set and the if the global interrupt enable bit in sreg is set. ? bit 6 ? spe: spi enable when the spe bit is written to one, the spi is enabled. this bit must be set to enable any spi operations. bit 1 bit 6 lsb msb sck (cpol = 0) mode 0 sample i mosi/miso change 0 mosi pin change 0 miso pin sck (cpol = 1) mode 2 ss msb lsb bit 6 bit 1 bit 5 bit 2 bit 4 bit 3 bit 3 bit 4 bit 2 bit 5 msb first (dord = 0) lsb first (dord = 1) sck (cpol = 0) mode 1 sample i mosi/miso change 0 mosi pin change 0 miso pin sck (cpol = 1) mode 3 ss msb lsb bit 6 bit 1 bit 5 bit 2 bit 4 bit 3 bit 3 bit 4 bit 2 bit 5 bit 1 bit 6 lsb msb msb first (dord = 0) lsb first (dord = 1) bit 76543210 0x2c (0x4c) spie spe dord mstr cpol cpha spr1 spr0 spcr read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 155 2570n?avr?05/11 atmega325/3250/645/6450 ? bit 5 ? dord: data order when the dord bit is written to one, the lsb of the data word is transmitted first. when the dord bit is written to zero, the msb of the data word is transmitted first. ? bit 4 ? mstr: master/slave select this bit selects master spi mode when written to one, and slave spi mode when written logic zero. if ss is configured as an input and is driven low while mstr is set, mstr will be cleared, and spif in spsr will become set. the user will th en have to set mstr to re-enable spi mas- ter mode. ? bit 3 ? cpol: clock polarity when this bit is written to one, sck is high when idle. when cpol is written to zero, sck is low when idle. refer to figure 19-3 and figure 19-4 for an example. the cpol functionality is sum- marized below: ? bit 2 ? cpha: clock phase the settings of the clock phase bit (cpha) determine if data is sampled on the leading (first) or trailing (last) edge of sck. refer to figure 19-3 and figure 19-4 for an example. the cpol functionality is summarized below: ? bits 1, 0 ? spr1, spr0: spi clock rate select 1 and 0 these two bits control the sck rate of the dev ice configured as a master. spr1 and spr0 have no effect on the slave. the relationship between sck and the oscillator clock frequency f osc is shown in the following table: table 19-3. cpol functionality cpol leading edge trailing edge 0 rising falling 1 falling rising table 19-4. cpha functionality cpha leading edge trailing edge 0 sample setup 1 setup sample table 19-5. relationship between sck and the oscillator frequency spi2x spr1 spr0 sck frequency 000 f osc / 4 001 f osc / 16 010 f osc / 64 011 f osc / 12 8 100 f osc / 2 101 f osc / 8 110 f osc / 32 111 f osc / 64 156 2570n?avr?05/11 atmega325/3250/645/6450 19.5.2 spsr ? spi status register ? bit 7 ? spif: spi interrupt flag when a serial transfer is complete, the spif flag is set. an interrupt is generated if spie in spcr is set and global interrupts are enabled. if ss is an input and is dr iven low when the spi is in master mode, this will also set the spif flag. spif is cleared by hardwa re when executing the corresponding interrupt handling vector. alternatively, the spif bit is cleared by first reading the spi status register with spif set, then accessing the spi data register (spdr). ? bit 6 ? wcol: write collision flag the wcol bit is set if the spi data register (spdr) is written during a data transfer. the wcol bit (and the spif bit) are cleared by first reading the spi status register with wcol set, and then accessing the spi data register. ? bit 5:1 ? reserved bits these bits are reserved bits in the atmel atmega325/3250/645/6450 and will always read as zero. ? bit 0 ? spi2x: double spi speed bit when this bit is written logi c one the spi speed (sck freque ncy) will be doubled when the spi is in master mode (see table 19-5 ). this means that the mini mum sck period will be two cpu clock periods. when the spi is configured as slave, the spi is only guaranteed to work at f osc /4 or lower. the spi interface on the atmel atmega325/3250/645/6450 is also used for program memory and eeprom downloading or uploading. see page 2 8 0 for serial programming and verification. 19.5.3 spdr ? spi data register the spi data register is a read/write register used for data transfer between the register file and the spi shift register. writing to the register initiates data transmission. reading the regis- ter causes the shift register receive buffer to be read. bit 76543210 0x2d (0x4d) spifwcol?????spi2xspsr read/writerrrrrrrr/w initial value00000000 bit 76543210 0x2e (0x4e) msb lsb spdr read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value x x x x x x x x undefined 157 2570n?avr?05/11 atmega325/3250/645/6450 20. usart0 20.1 features the universal synchronous and asynchronous serial receiver and transmitter (usart) is a highly flexible serial communication device. the main features are: ? full duplex operation (independent se rial receive and transmit registers) ? asynchronous or synchronous operation ? master or slave clocked synchronous operation ? high resolution baud rate generator ? supports serial frames with 5, 6, 7, 8, or 9 data bits and 1 or 2 stop bits ? odd or even parity generation and parity check supported by hardware ? data overrun detection ? framing error detection ? noise filtering includes false start bit detection and digital low pass filter ? three separate interrupts on tx complete, tx data register empty and rx complete ? multi-processor communication mode ? double speed asynchronous communication mode 20.2 overview a simplified block diagram of the usart transmitter is shown in figure 20-1 . cpu accessible i/o registers and i/o pins are shown in bold. the power reduction usart bit, prusart0, in ?power reduction register? on page 37 must be written to zero to enable the usart0 module. 158 2570n?avr?05/11 atmega325/3250/645/6450 figure 20-1. usart block diagram (1) note: 1. refer to figure 1-1 on page 2 , figure 1-2 on page 3 and ?alternate functions of port e? on page 72 for usart pin placement. parity generator ubrr[h:l] udr (transmit) ucsra ucsrb ucsrc baud rate generator transmit shift register receive shift register rxd txd pin control udr (receive) pin control xck data recovery clock recovery pin control tx control rx control parity checker data bus osc sync logic clock generator transmitter receiver 159 2570n?avr?05/11 atmega325/3250/645/6450 the dashed boxes in the block diagram separate the three main parts of the usart (listed from the top): clock generator, transmitter and receiver. control registers are shared by all units. the clock generation logic consis ts of synchronization logic fo r external clock input used by synchronous slave operation, and the baud rate generator. the xck (transfer clock) pin is only used by synchronous transfer mode. the transmitter consists of a single write buffer, a serial shift register, parity generator and control logic for handling different serial frame formats. the write buffer allows a continuous transfer of data without any delay between frames. the receiver is the most complex part of the usart module due to its clock and data recovery units. the recovery units are used for asynchronous data reception. in addition to the recovery units, the receiver includes a parity checker, control logic, a shift register and a two level receive buffer (udrn). the receiver supports the same frame formats as the transmitter, and can detect frame error, data overrun and parity errors. 20.2.1 avr usart vs. avr uart ? compatibility the usart is fully compatible with the avr uart regarding: ? bit locations inside all usart registers. ? baud rate generation. ? transmitter operation. ? transmit buffer functionality. ? receiver operation. however, the receive bu ffering has two improvements that will affect the comp atibility in some special cases: ? a second buffer register has been added. the two buffer registers operate as a circular fifo buffer. therefore the udrn must only be read once for each incoming data! more important is the fact that the error flags (fen and dorn) and the ninth data bit (rxb 8 n) are buffered with the data in the receive buffer. therefore the status bits must always be read before the udrn register is read. otherwise th e error status will be lost since the buffer state is lost. ? the receiver shift register can now act as a th ird buffer level. this is done by allowing the received data to remain in the serial shift register (see figure 20-1 ) if the buffer registers are full, until a new start bit is detected. the usart is therefore more resistant to data overrun (dorn) error conditions. the following control bits have changed name, but have same functionality and register location: ? chr9 is changed to ucszn2. ? or is changed to dorn. 20.3 clock generation the clock generation logic generates the base clock for the transmitter and receiver. the usart supports four modes of clock operati on: normal asynchronous, double speed asyn- chronous, master synchronous and slave synchronous mode. the umseln bit in usart control and status register c (ucsrnc) selects between asynchronous and synchronous operation. double speed (asynchronous mode only) is controlled by the u2xn found in the ucsrna register. when using synchronous mode (umseln = 1), the data direction register for the xck pin (ddr_xck) controls whether t he clock source is internal (master mode) or external (slave mode). the xck pin is only active when using synchronous mode. figure 20-2 shows a block diagram of the clock generation logic. 160 2570n?avr?05/11 atmega325/3250/645/6450 figure 20-2. clock generation logic, block diagram signal description: txclk transmitter clock (internal signal). rxclk receiver base clock (internal signal). xcki input from xck pin (internal signal). used for synchronous slave operation. xcko clock output to xck pin (internal signal). used for synchronous master operation. fosc xtal pin frequency (system clock). 20.3.1 internal clock generation ? the baud rate generator internal clock generation is used for the as ynchronous and the synchronous master modes of operation. the description in this section refers to figure 20-2 . the usart baud rate register (ubrr) and the down-counter connected to it function as a programmable prescaler or baud rate generator. the down-counter, running at system clock (f osc ), is loaded with the ubrr value each time the counter has counted down to zero or when the ubrrl register is written. a clock is gener ated each time the counter reaches zero. this clock is the baud rate ge nerator clock output (= f osc /(ubrr+1)). the transmitter divides the baud rate generator clock output by 2, 8 or 16 depending on mode. the baud rate generator out- put is used directly by the receiver?s clock an d data recovery units. however, the recovery units use a state machine that uses 2, 8 or 16 states depending on mode set by the state of the umseln, u2xn and ddr_xck bits. table 20-1 contains equations for calculating the baud rate (in bits per second) and for calculat- ing the ubrr value for each mode of operation using an internally generated clock source. prescaling down-counter /2 ubrr /4 /2 fosc ubrr+1 sync register osc xck pin txclk u2x umsel ddr_xck 0 1 0 1 xcki xcko ddr_xck rxclk 0 1 1 0 edge detector ucpol 161 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. the baud rate is defined to be the transfer rate in bit per second (bps) baud baud rate (in bits per second, bps) f osc system oscillator clock frequency ubrr contents of the ubrrh and ubrrl registers, (0-4095) some examples of ubrr values for so me system clock frequencies are found in table 20-4 (see page 176 ). 20.3.2 double speed operation (u2xn) the transfer rate can be doubled by setting the u2xn bit in ucsrna. setting this bit only has effect for the asynchronous operation. set this bit to zero when using synchronous operation. setting this bit will reduce the divisor of the baud rate divider from 16 to 8 , effectively doubling the transfer rate for asynchronous communication. note however that the receiver will in this case only use half the number of samples (reduced from 16 to 8 ) for data sampling and clock recovery, and therefore a more accurate baud rate setting and system clock are required when this mode is used. for the transmitter, there are no downsides. 20.3.3 external clock external clocking is used by the synchronous sl ave modes of operation. the description in this section refers to figure 20-2 for details. external clock input from the xck pin is sampled by a synchronization register to minimize the chance of meta-stability. the output from the synchronization register must then pass through an edge detector before it can be used by the transmitter and receiver. this process intro- duces a two cpu clock period delay and theref ore the maximum external xck clock frequency is limited by the following equation: note that f osc depends on the stability of the system clock source. it is therefore recommended to add some margin to avoid possible loss of data due to frequency variations. 20.3.4 synchronous clock operation when synchronous mode is used (umseln = 1), the xck pin will be used as either clock input (slave) or clock output (master). the dependency between the clock edges and data sampling table 20-1. equations for calculating baud rate register setting operating mode equation for calculating baud rate (1) equation for calculating ubrr value asynchronous normal mode (u2xn = 0) asynchronous double speed mode (u2xn = 1) synchronous master mode baud f osc 16 ubrr 1 + () -------------------------------------- - = ubrr f osc 16 baud ----------------------- - 1 ? = baud f osc 8 ubrr 1 + () ----------------------------------- = ubrr f osc 8 baud -------------------- 1 ? = baud f osc 2 ubrr 1 + () ----------------------------------- = ubrr f osc 2 baud -------------------- 1 ? = f xck f osc 4 ----------- < 162 2570n?avr?05/11 atmega325/3250/645/6450 or data change is the same. the basic principle is that data input (on rxd) is sampled at the opposite xck clock edge of the edge the data output (txd) is changed. figure 20-3. synchronous mode xck timing. the ucpoln bit in ucsrnc selects which xck cloc k edge is used for data sampling and which is used for data change. as figure 20-3 shows, when ucpoln is ze ro the data will be changed at rising xck edge and sampled at falling xck ed ge. if ucpoln is set, the data will be changed at falling xck edge and samp led at rising xck edge. 20.4 frame formats a serial frame is defined to be one character of da ta bits with synchronizat ion bits (start and stop bits), and optionally a parity bi t for error checking. the usart accepts all 30 combinations of the following as valid frame formats: ? 1 start bit ?5, 6, 7, 8 , or 9 data bits ? no, even or odd parity bit ? 1 or 2 stop bits a frame starts with the start bit followed by the least significant data bit. then the next data bits, up to a total of nine, are succeeding, ending with t he most significant bit. if enabled, the parity bit is inserted after the data bits, before the stop bits. when a complete frame is transmitted, it can be directly followed by a new frame, or the communication line can be set to an idle (high) state. figure 20-4 illustrates the possible combinations of th e frame formats. bits inside brackets are optional. rxd / txd xck rxd / txd xck ucpol = 0 ucpol = 1 sample sample 163 2570n?avr?05/11 atmega325/3250/645/6450 figure 20-4. frame formats st start bit, always low. (n) data bits (0 to 8 ). p parity bit. can be odd or even. sp stop bit, always high. idle no transfers on the communication line (rxd or txd). an idle line must be high. the frame format used by th e usart is set by the ucszn2:0, upmn1:0 and usbsn bits in ucsrnb and ucsrnc. the receiver and transmitter use the same setting. note that changing the setting of any of these bits will corrupt a ll ongoing communication for both the receiver and transmitter. the usart character size (ucszn2:0) bits select the number of data bits in the frame. the usart parity mode (upmn1:0) bits enable and set the type of parity bit. the selection between one or two stop bits is done by the usart stop bit select (usbsn) bit. the re ceiver ignores the second stop bit. an fen (frame error) will ther efore only be detected in the cases where the first stop bit is zero. 20.4.1 parity bit calculation the parity bit is calculated by do ing an exclusive-or of all the data bits. if odd parity is used, the result of the exclusive or is inverted. the re lation between the parity bit and data bits is as follows: p even parity bit using even parity p odd parity bit using odd parity d n data bit n of the character if used, the parity bit is located between the last data bit and first stop bit of a serial frame. 20.5 usart initialization the usart has to be initialized before any communication can take place. the initialization pro- cess normally consists of setting the baud rate, setting frame format and enabling the transmitter or the receiver depending on the usage. for interrupt driven usart operation, the global interrupt flag should be cleared (and interrupts globally disabled) when doing the initialization. 1 0 2 3 4 [5] [6] [7] [8] [p] st sp1 [sp2] (st / idle) (idle) frame p even d n 1 ? d 3 d 2 d 1 d 0 0 p odd d n 1 ? d 3 d 2 d 1 d 0 1 = = 164 2570n?avr?05/11 atmega325/3250/645/6450 before doing a re-initialization with changed baud rate or frame format, be sure that there are no ongoing transmissions during the period the registers are changed. the txcn flag can be used to check that the transmitter has completed all transfers, and the rxcn flag can be used to check that there are no unread data in the receive buffer. note that the txcn flag must be cleared before each transmission (before udrn is written) if it is used for this purpose. the following simple usart initialization code examples show one assembly and one c func- tion that are equal in functionality. the exampl es assume asynchronous operation using polling (no interrupts enabled) and a fixed frame format. the baud rate is given as a function parameter. for the assembly code, the baud rate parameter is assumed to be stored in the r17:r16 registers. note: 1. see ?about code examples? on page 9 . assembly code example (1) usart_init: ; set baud rate out ubrrh, r17 out ubrrl, r16 ; enable receiver and transmitter ldi r16, (1< 168 2570n?avr?05/11 atmega325/3250/645/6450 the following code example shows a simple us art receive function based on polling of the receive complete (rxcn) flag. when using frames with less than eight bits the most significant bits of the data read from the udrn will be masked to zero. th e usart has to be initialized before the function can be used. note: 1. see ?about code examples? on page 9 . the function simply waits for data to be present in the receive buffer by checking the rxcn flag, before reading the buffer and returning the value. 20.7.2 receiving frames with 9 data bits if 9-bit characters are used (ucsz=7) t he ninth bit must be read from the rxb 8 n bit in ucsrnb before reading the low bits from the udrn. this ru le applies to the fen, dorn and upen sta- tus flags as well. read status from ucsrna, then data from udrn . reading the udrn i/o location will change the stat e of the receive bu ffer fifo and c onsequently the txb 8 n, fen, dorn and upen bits, which all ar e stored in the fifo, will change. assembly code example (1) usart_receive: ; wait for data to be received sbis ucsr0a, rxc0 rjmp usart_receive ; get and return received data from buffer in r16, udr0 ret c code example (1) unsigned char usart_receive( void ) { /* wait for data to be received */ while ( !(ucsr0a & (1< 170 2570n?avr?05/11 atmega325/3250/645/6450 20.7.3 receive compete flag and interrupt the usart receiver has one flag that indicates the receiver state. the receive complete (rxcn) flag indicates if there are unread data present in the receive buf- fer. this flag is one when unread data exist in the receive buffer, and zero when the receive buffer is empty (i.e., does not contain any unread data). if the receiver is disabled (rxenn = 0), the receive buffer will be flushed and cons equently the rxcn bit will become zero. when the receive complete interrupt enable (r xcien) in ucsrnb is set, the usart receive complete interrupt will be executed as long as the rxcn flag is se t (provided that global inter- rupts are enabled). when interrupt-driven data reception is used, the receive complete routine must read the received data from udrn in order to clear the rxcn flag, otherwise a new inter- rupt will occur once the inte rrupt routine terminates. 20.7.4 receiver error flags the usart receiver has three error flags: frame error (fen), data overrun (dorn) and parity error (upen). all can be accessed by reading ucsrna. common for the error flags is that they are located in the receive buffer together with the frame for which they indicate the error status. due to the buffering of the error flags, the ucsrna must be read before the receive buffer (udrn), since reading the udrn i/o location change s the buffer read location. another equality for the error flags is that they can not be altered by software doing a write to the flag location. however, all flags must be set to zero when the ucsrna is written for upward compatibility of future usart impl ementations. none of the error flags can genera te interrupts. the frame error (fen) flag indicates the state of the first stop bit of the next readable frame stored in the receive buffer. the fen flag is zero when the stop bit was correctly read (as one), and the fen flag will be one when the stop bit was incorrect (zero). this flag can be used for detecting out-of-sync conditions, detecting break conditions and protocol handling. the fen flag is not affected by the setting of the u sbsn bit in ucsrnc since the receiver ignores all, except for the first, stop bits. for compatibility with future devices, always set this bit to zero when writing to ucsrna. the data overrun (dorn) flag indicates data loss due to a receiver buffer full condition. a data overrun occurs when the receive buffer is full (two characters), it is a new character wait- ing in the receive shift register, and a new start bit is detected. if the dorn flag is set there was one or more serial frame lost between the frame last read from udrn, and the next frame read from udrn. for compatibility wi th future devices, always write this bit to zero when writing to ucsrna. the dorn flag is cleared when t he frame received was successfully moved from the shift register to the receive buffer. the parity error (upen) flag indicates that the next frame in the receive buffer had a parity error when received. if parity check is not enabled the upen bit will always be read zero. for compatibility with future devices, always set this bit to zero when writing to ucsrna. for more details see ?parity bit calculation? on page 163 and ?parity checker? on page 170 . 20.7.5 parity checker the parity checker is active when the high usart parity mode (upmn1) bit is set. type of par- ity check to be performed (odd or even) is selected by the upmn0 bit. when enabled, the parity checker calculates the parity of the data bits in incoming frames and compares the result with the parity bit from the serial frame. the result of the check is stored in the receive buffer together with the received data and stop bits. the parity error (upen) flag can then be read by software to check if the frame had a parity error. 171 2570n?avr?05/11 atmega325/3250/645/6450 the upen bit is set if the next character that can be read from the receive buffer had a parity error when received and the parity checking was enabled at that point (upmn1 = 1). this bit is valid until the receive buffer (udrn) is read. 20.7.6 disabling the receiver in contrast to the transmitter, disabling of the receiver will be immediate. data from ongoing receptions will therefore be lost. when disabled (i .e., the rxenn is set to zero) the receiver will no longer override the normal function of the rxd port pin. the receiver buffer fifo will be flushed when the receiver is disabled. remaining data in the buffer will be lost 20.7.7 flushing the receive buffer the receiver buffer fifo will be fl ushed when the receiver is disa bled, i.e., the buffer will be emptied of its contents. unread data will be lost. if the buffer has to be flushed during normal operation, due to for in stance an error conditi on, read the udrn i/o location until the rxcn flag is cleared. the following code example shows how to flush the receive buffer. note: 1. see ?about code examples? on page 9 . 20.8 asynchronous data reception the usart includes a clock recovery and a data recovery unit for handling asynchronous data reception. the clock recovery logic is used fo r synchronizing the internally generated baud rate clock to the incoming asynchronous serial frames at the rxd pin. the data recovery logic sam- ples and low pass filters each incoming bit, ther eby improving the noise immunity of the receiver. the asynchronous reception operational range depends on the accuracy of the inter- nal baud rate clock, the rate of the incoming frames, and the frame size in number of bits. 20.8.1 asynchronous clock recovery the clock recovery logic synchronizes internal clock to the incoming serial frames. figure 20-5 illustrates the sampling process of th e start bit of an incoming frame. the sample rate is 16 times the baud rate for normal mode, and eight times the baud rate for double speed mode. the hor- izontal arrows illustrate the sy nchronization variation due to t he sampling process. note the larger time variation when using the double speed mode (u2xn = 1) of operation. samples denoted zero are samples done when the rxd line is idle (i.e., no communication activity). assembly code example (1) usart_flush: sbis ucsr0a, rxc0 ret in r16, udr0 rjmp usart_flush c code example (1) void usart_flush( void ) { unsigned char dummy; while ( ucsr0a & (1< 173 2570n?avr?05/11 atmega325/3250/645/6450 figure 20-7. stop bit sampling and ne xt start bit sampling the same majority voting is done to the stop bit as done for the other bits in the frame. if the stop bit is registered to have a logic 0 va lue, the frame error (fen) flag will be set. a new high to low transition indicating the start bit of a new frame can come right after the last of the bits used for majority voting. for normal speed mode, the first low level sample can be at point marked (a) in figure 20-7 . for double speed mode the first low level must be delayed to (b). (c) marks a stop bit of full length. the ear ly start bit detection influences the operational range of the receiver. 20.8.3 asynchronous operational range the operational range of the receiver is dependent on the mismatch between the received bit rate and the internally generated baud rate. if the transmitter is sending frames at too fast or too slow bit rates, or the internally generated baud rate of the receiver does not have a similar (see table 20-2 ) base frequency, the receiver will not be abl e to synchronize the frames to the start bit. the following equations can be used to calculate the ratio of the incoming data rate and internal receiver baud rate. d sum of character size and parity size (d = 5 to 10 bit) s samples per bit. s = 16 for normal speed mode and s = 8 for double speed mode. s f first sample number used for majority voting. s f = 8 for normal speed and s f = 4 for double speed mode. s m middle sample number used for majority voting. s m = 9 for normal speed and s m = 5 for double speed mode. r slow is the ratio of the slowest incoming data rate that can be accepted in relation to the receiver baud rate. r fast is the ratio of the fastest incoming data rate that can be accepted in relation to the receiver baud rate. table 20-2 and table 20-3 list the maximum receiver baud rate error that can be tolerated. note that normal speed mode has higher toleration of baud rate variations. 1234567 8 9 10 0/1 0/1 0/1 stop 1 123 4 5 6 0/1 rxd sample (u2x = 0) sample (u2x = 1) (a) (b) (c) r slow d 1 + () s s 1 ? ds ? s f ++ ------------------------------------------ - = r fast d 2 + () s d 1 + () ss m + ----------------------------------- = 174 2570n?avr?05/11 atmega325/3250/645/6450 the recommendations of the maximum receiver baud rate error was made under the assump- tion that the receiver and transmitter equally divides the maximum total error. there are two possible sources fo r the receivers baud rate erro r. the receiver?s system clock (xtal) will always have some minor instabilit y over the supply voltage range and the tempera- ture range. when using a crystal to generate the system clock, this is rarely a problem, but for a resonator the system clock may differ more than 2% depending of the resonators tolerance. the second source for the error is more controllable. the baud rate generator can not always do an exact division of the system frequency to get the b aud rate wanted. in this case an ubrr value that gives an acceptable low error can be used if possible. 20.9 multi-processor communication mode setting the multi-processor communication m ode (mpcmn) bit in ucsrna enables a filtering function of incoming frames received by the usart receiver. frames that do not contain address information will be ignored and not put in to the receive buffer. this effectively reduces the number of incoming frames that has to be handled by the cpu, in a system with multiple mcus that communicate via the same serial bu s. the transmitter is unaffected by the mpcmn setting, but has to be used diffe rently when it is a part of a system utilizing the multi-processor communication mode. if the receiver is set up to receive frames that contain 5 to 8 data bits, then the first stop bit indi- cates if the frame contains data or address information. if the receiver is set up for frames with table 20-2. recommended maximum receiver baud rate error for normal speed mode (u2xn = 0) d # (data+parity bit) r slow (%) r fast (%) max total error (%) recommended max receiver error (%) 5 93.20 106.67 +6.67/-6. 8 3.0 6 94.12 105.79 +5.79/-5. 88 2.5 794. 8 1 105.11 +5.11/-5.19 2.0 8 95.36 104.5 8 +4.5 8 /-4.54 2.0 995. 8 1 104.14 +4.14/-4.19 1.5 10 96.17 103.7 8 +3.7 8 /-3. 8 3 1.5 table 20-3. recommended maximum receiver baud rate error for double speed mode (u2xn = 1) d # (data+parity bit) r slow (%) r fast (%) max total error (%) recommended max receiver error (%) 5 94.12 105.66 +5.66/-5. 88 2.5 6 94.92 104.92 +4.92/-5.0 8 2.0 7 95.52 104,35 +4.35/-4.4 8 1.5 8 96.00 103.90 +3.90/-4.00 1.5 9 96.39 103.53 +3.53/-3.61 1.5 10 96.70 103.23 +3.23/-3.30 1.0 175 2570n?avr?05/11 atmega325/3250/645/6450 nine data bits, then the ninth bit (rxb 8 n) is used for identifying address and data frames. when the frame type bit (the first stop or the ninth bit) is one, the frame contains an address. when the frame type bit is zero the frame is a data frame. the multi-processor communication mode enables several slave mcus to receive data from a master mcu. this is done by first decoding an address frame to find out which mcu has been addressed. if a particular slave mcu has been addressed, it will rece ive the following data frames as normal, while the other slave mcus will ignore the received frames until another address frame is received. 20.9.1 using mpcmn for an mcu to act as a master mcu, it can use a 9-bit character frame format (ucsz = 7). the ninth bit (txb 8 n) must be set when an address frame (txb 8 n = 1) or cleared when a data frame (txb = 0) is being transmitted. the slave mcus must in this case be set to use a 9-bit character frame format. the following procedure should be used to exchange data in multi-processor communication mode: 1. all slave mcus are in multi-processor communication mode (mpcmn in ucsrna is set). 2. the master mcu sends an address frame, and all slaves receive and read this frame. in the slave mcus, the rxcn flag in ucsrna will be set as normal. 3. each slave mcu reads the udrn register and determines if it has been selected. if so, it clears the mpcmn bit in ucsrna, otherwise it waits for the next address byte and keeps the mpcmn setting. 4. the addressed mcu will receive all data fram es until a new address frame is received. the other slave mcus, which still have the mp cmn bit set, will ignore the data frames. 5. when the last data frame is received by the addressed mcu, the addressed mcu sets the mpcmn bit and waits for a new address frame from master. the process then repeats from 2. using any of the 5- to 8 -bit character frame formats is possible, but impractical since the receiver must change between using n and n+1 character frame formats. this makes full- duplex operation difficult since the transmitter a nd receiver uses the same character size set- ting. if 5- to 8 -bit character frames are used, the transmitter must be set to use two stop bit (usbsn = 1) since the first stop bit is used for indicating the frame type. do not use read-modify-write in structions (sbi and cbi) to set or clear the mpcmn bit. the mpcmn bit shares the same i/o location as the txcn flag and this might accidentally be cleared when using sbi or cbi instructions. 176 2570n?avr?05/11 atmega325/3250/645/6450 20.10 examples of ba ud rate setting for standard crystal and resonator frequencies, the most commonly used baud rates for asyn- chronous operation can be generated by using the ubrr settings in table 20-4 . ubrr values which yield an actual baud rate differing less than 0.5% from the target baud rate, are bold in the table. higher error ratings are acceptable, but the receiver will have less noise resistance when the error ratings are high, especially for large serial frames (see ?asynchronous operational range? on page 173 ). the error values are calculated using the following equation: error[%] baudrate closest match baudrate -------------------------------------------------------- 1 ? ?? ?? 100% ? = table 20-4. examples of ubrr settings for co mmonly used oscillator frequencies baud rate (bps) f osc = 1.0000 mhz f osc = 1.8432 mhz f osc = 2.0000 mhz u2xn = 0u2xn = 1u2xn = 0u2xn = 1u2xn = 0u2xn = 1 ubrr error ubrr error ubrr error ubrr error ubrr error ubrr error 2400 25 0.2% 51 0.2% 47 0.0% 95 0.0% 51 0.2% 103 0.2% 4 8 00 12 0.2% 25 0.2% 23 0.0% 47 0.0% 25 0.2% 51 0.2% 9600 6 -7.0% 12 0.2% 11 0.0% 23 0.0% 12 0.2% 25 0.2% 14.4k 3 8 .5% 8 -3.5% 70.0%150.0% 8 -3.5% 16 2.1% 19.2k 2 8 .5% 6 -7.0% 50.0%110.0% 6 -7.0% 12 0.2% 2 8 . 8 k1 8 .5% 3 8 .5% 3 0.0% 7 0.0% 3 8 .5% 8 -3.5% 3 8 .4k 1 -1 8 .6% 2 8 .5% 2 0.0% 5 0.0% 2 8 .5% 6 -7.0% 57.6k 0 8 .5% 1 8 .5% 1 0.0% 3 0.0% 1 8 .5% 3 8 .5% 76. 8 k? ? 1-1 8 .6% 1 -25.0% 20.0% 1-1 8 .6% 2 8 .5% 115.2k ? ? 0 8 .5% 0 0.0% 1 0.0% 0 8 .5% 1 8 .5% 230.4k ? ? ? ? ? ? 00.0% ???? 250k??????????00.0% max. (1) 62.5 kbps 125 kbps 115.2 kbps 2 30.4 kbps 125 kbps 250 kbps 1. ubrr = 0, error = 0.0% 177 2570n?avr?05/11 atmega325/3250/645/6450 table 20-5. examples of ubrr settings for commonly used oscillator frequencies (continued) baud rate (bps) f osc = 3.6864 mhz f osc = 4.0000 mhz f osc = 7.3728 mhz u2xn = 0u2xn = 1u2xn = 0u2xn = 1u2xn = 0u2xn = 1 ubrr error ubrr error ubrr error ubrr error ubrr error ubrr error 2400 95 0.0% 191 0.0% 103 0.2% 207 0.2% 191 0.0% 383 0.0% 4 8 00 47 0.0% 95 0.0% 51 0.2% 103 0.2% 95 0.0% 191 0.0% 9600 23 0.0% 47 0.0% 25 0.2% 51 0.2% 47 0.0% 95 0.0% 14.4k 15 0.0% 31 0.0% 16 2.1% 34 -0. 8 % 31 0.0% 63 0.0% 19.2k 11 0.0% 23 0.0% 12 0.2% 25 0.2% 23 0.0% 47 0.0% 2 8 . 8 k 7 0.0% 15 0.0% 8 -3.5% 16 2.1% 15 0.0% 31 0.0% 3 8 .4k 5 0.0% 11 0.0% 6 -7.0% 12 0.2% 11 0.0% 23 0.0% 57.6k 3 0.0% 7 0.0% 3 8 .5% 8 -3.5% 70.0%150.0% 76. 8 k 2 0.0% 5 0.0% 2 8 .5% 6 -7.0% 50.0%110.0% 115.2k 1 0.0% 3 0.0% 1 8 .5% 3 8 .5% 30.0%70.0% 230.4k 0 0.0% 1 0.0% 0 8 .5% 1 8 .5% 10.0%30.0% 250k 0 -7. 8 %1-7. 8 % 0 0.0% 1 0.0% 1-7. 8 %3-7. 8 % 0.5m ? ? 0 -7. 8 %? ? 00.0% 0-7. 8 %1-7. 8 % 1m ??????????0-7. 8 % max. (1) 230.4 kbps 460. 8 kbps 250 kbps 0.5 mbps 460. 8 kbps 921.6 kbps 1. ubrr = 0, error = 0.0% 178 2570n?avr?05/11 atmega325/3250/645/6450 table 20-6. examples of ubrr settings for commonly used oscillator frequencies (continued) baud rate (bps) f osc = 8.0000 mhz f osc = 11.0592 mhz f osc = 14.7456 mhz u2xn = 0u2xn = 1u2xn = 0u2xn = 1u2xn = 0u2xn = 1 ubrr error ubrr error ubrr error ubrr error ubrr error ubrr error 2400 207 0.2% 416 -0.1% 287 0.0% 575 0.0% 383 0.0% 767 0.0% 4 8 00 103 0.2% 207 0.2% 143 0.0% 287 0.0% 191 0.0% 383 0.0% 9600 51 0.2% 103 0.2% 71 0.0% 143 0.0% 95 0.0% 191 0.0% 14.4k 34 -0. 8 %6 8 0.6% 47 0.0% 95 0.0% 63 0.0% 127 0.0% 19.2k 25 0.2% 51 0.2% 35 0.0% 71 0.0% 47 0.0% 95 0.0% 2 8 . 8 k162.1%34-0. 8 % 23 0.0% 47 0.0% 31 0.0% 63 0.0% 3 8 .4k 12 0.2% 25 0.2% 17 0.0% 35 0.0% 23 0.0% 47 0.0% 57.6k 8 -3.5% 16 2.1% 11 0.0% 23 0.0% 15 0.0% 31 0.0% 76. 8 k6-7.0% 12 0.2% 8 0.0% 17 0.0% 11 0.0% 23 0.0% 115.2k 3 8 .5% 8 -3.5% 5 0.0% 11 0.0% 7 0.0% 15 0.0% 230.4k 1 8 .5% 3 8 .5% 2 0.0% 5 0.0% 3 0.0% 7 0.0% 250k 1 0.0% 3 0.0% 2-7. 8 %5-7. 8 %3-7. 8 %6 5.3% 0.5m 0 0.0% 1 0.0% ??2-7. 8 %1-7. 8 %3-7. 8 % 1m ? ? 00.0% ????0-7. 8 %1-7. 8 % max. (1) 0.5 mbps 1 mbps 691.2 kbps 1.3 8 24 mbps 921.6 kbps 1. 8 432 mbps 1. ubrr = 0, error = 0.0% 179 2570n?avr?05/11 atmega325/3250/645/6450 20.11 register description 20.11.1 udrn ? usart i/o data register n the usart transmit data buffer register and usart receive data buffer registers share the same i/o address re ferred to as usart data register or udrn. the transmit data buffer reg- ister (txb) will be the destination for data wri tten to the udrn register location. reading the udrn register location will retu rn the contents of the receiv e data buffer register (rxb). for 5-, 6-, or 7-bit char acters the upper unu sed bits will be ignored by the transmitter and set to zero by the receiver. the transmit buffer can only be written when the udren flag in the ucsrna register is set. data written to udrn wh en the udren flag is not set, will be ignored by the usart transmit- ter. when data is written to the transmit buffer, and the transmitter is enabled, the transmitter will load the data into the transmit shift regist er when the shift register is empty. then the data will be serially tr ansmitted on the txd pin. table 20-7. examples of ubrr settings for commonly used oscillator frequencies (continued) baud rate (bps) f osc = 16.0000 mhz f osc = 18.4320 mhz f osc = 20.0000 mhz u2xn = 0u2xn = 1u2xn = 0u2xn = 1u2xn = 0u2xn = 1 ubrr error ubrr error ubrr error ubrr error ubrr error ubrr error 2400 416 -0.1% 832 0.0% 479 0.0% 959 0.0% 520 0.0% 1041 0.0% 4 8 00 207 0.2% 416 -0.1% 239 0.0% 479 0.0% 259 0.2% 520 0.0% 9600 103 0.2% 207 0.2% 119 0.0% 239 0.0% 129 0.2% 259 0.2% 14.4k 6 8 0.6% 138 -0.1% 79 0.0% 159 0.0% 86 -0.2% 173 -0.2% 19.2k 51 0.2% 103 0.2% 59 0.0% 119 0.0% 64 0.2% 129 0.2% 2 8 . 8 k34-0. 8 %6 8 0.6% 39 0.0% 79 0.0% 42 0.9% 86 -0.2% 3 8 .4k 25 0.2% 51 0.2% 29 0.0% 59 0.0% 32 -1.4% 64 0.2% 57.6k 16 2.1% 34 -0. 8 % 19 0.0% 39 0.0% 21 -1.4% 42 0.9% 76. 8 k 12 0.2% 25 0.2% 14 0.0% 29 0.0% 15 1.7% 32 -1.4% 115.2k 8 -3.5% 16 2.1% 90.0%190.0% 10 -1.4% 21 -1.4% 230.4k 3 8 .5% 8 -3.5% 4 0.0% 9 0.0% 4 8 .5% 10 -1.4% 250k 3 0.0% 7 0.0% 4-7. 8 % 8 2.4% 40.0%90.0% 0.5m 1 0.0% 3 0.0% ??4-7. 8 %??40.0% 1m 0 0.0% 1 0.0% ???????? max. (1) 1 mbps 2 mbps 1.152 mbps 2.3 04 mbps 1.25 mbps 2.5 mbps 1. ubrr = 0, error = 0.0% bit 76543210 rxb[7:0] udrn (read) txb[7:0] udrn (write) read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 180 2570n?avr?05/11 atmega325/3250/645/6450 the receive buffer consists of a two level fifo . the fifo will change its state whenever the receive buffer is accessed. due to this behavior of the receive buffer, do not use read-modify- write instructions (sbi and cbi) on this location. be careful when using bit test instructions (sbic and sbis), since these also will change the state of the fifo. 20.11.2 ucsrna ? usart contro l and status register n a ? bit 7 ? rxcn: usart receive complete this flag bit is set when there are unread data in the receive buffer and cleared when the receive buffer is empty (i.e., does not contain any unread dat a). if the receiver is disabled, the receive buffer will be flushed and consequently the rxcn bit will become zero. the rxcn flag can be used to generate a receive complete interr upt (see description of the rxcien bit). ? bit 6 ? txcn: usart transmit complete this flag bit is set when the entire frame in the transmit shift register has been shifted out and there are no new data currently present in the transmit buffer (udrn). the txcn flag bit is auto- matically cleared when a transmit complete interrupt is executed, or it can be cleared by writing a one to its bit location. the txcn flag can generate a transmit complete interrupt (see description of the txcien bit). ? bit 5 ? udren: usart data register empty the udren flag indicates if the transmit buff er (udrn) is ready to receive new data. if udren is one, the buffer is empty, and therefore ready to be written. the udren flag can generate a data register empty interrupt (see description of the udrien bit). udren is set after a reset to indicate that the transmitter is ready. ? bit 4 ? fen: frame error this bit is set if the next character in the receive buffer had a frame error when received. i.e., when the first stop bit of the next character in the receive buffer is zero. this bit is valid until the receive buffer (udrn) is read. the fen bit is zero when the stop bit of received data is one. always set this bit to ze ro when writing to ucsrna. ? bit 3 ? dorn: data overrun this bit is set if a data overrun condition is detected. a data overrun occurs when the receive buffer is full (two characters), it is a new char acter waiting in the receive shift register, and a new start bit is detected. this bi t is valid until the receive buffer (udrn) is read . always set this bit to zero when writing to ucsrna. ? bit 2 ? upen: usart parity error this bit is set if the next character in the receive buffer had a parity error when received and the parity checking was enabled at that point (upmn1 = 1). this bit is valid until the receive buffer (udrn) is read. always set this bit to zero when writing to ucsrna. bit 7654321 0 rxcn txcn udren fen dorn upen u2xn mpcmn ucsrna read/writerr/wrrrrr/wr/w initial value0010000 0 181 2570n?avr?05/11 atmega325/3250/645/6450 ? bit 1 ? u2xn: double the usart transmission speed this bit only has effect for the asynchronous operation. write this bit to zero when using syn- chronous operation. writing this bit to one will re duce the divisor of the baud rate divider from 16 to 8 effectively dou- bling the transfer rate for asynchronous communication. ? bit 0 ? mpcmn: multi-processor communication mode this bit enables the multi-processor communica tion mode. when the mpcmn bit is written to one, all the incoming frames received by the usart receiver that do not contain address infor- mation will be ignored. the transmitter is unaffe cted by the mpcmn setting. for more detailed information see ?multi-processor communication mode? on page 174 . 20.11.3 ucsrnb ? usart contro l and status register n b ? bit 7 ? rxcien: rx co mplete interrupt enable writing this bit to one enables interrupt on the rxcn flag. a usart rece ive complete interrupt will be generated only if the rxcien bit is written to one, the global interrupt flag in sreg is written to one and the rxcn bit in ucsrna is set. ? bit 6 ? txcien: tx complete interrupt enable writing this bit to one enables interrupt on the txcn flag. a usart trans mit complete interrupt will be generated only if the txcien bit is written to one, the global interrupt flag in sreg is written to one and the txcn bit in ucsrna is set. ? bit 5 ? udrien: usart data register empty interrupt enable writing this bit to one enables interrupt on the udren flag. a data register empty interrupt will be generated only if the udrien bit is written to one, the global interrupt flag in sreg is written to one and the udren bit in ucsrna is set. ? bit 4 ? rxenn: receiver enable writing this bit to one enables the usart receiv er. the receiver will override normal port oper- ation for the rxd pin when enabled. disabling the receiver will flush the receive buffer invalidating the fen, dorn, and upen flags. ? bit 3 ? txenn: transmitter enable writing this bit to one enables the usart tr ansmitter. the transmitter will override normal port operation for the txd pin when enabled. the disa bling of the transmitter (writing txenn to zero) will not become effective until ongoing a nd pending transmissions are completed, i.e., when the transmit shift register and transmit buffer register do not contain data to be trans- mitted. when disabled, the transmitter will no longer override the txd port. bit 76543 2 10 rxcien txcien udrien rxenn txenn ucszn2 rxb8n txb8n ucsrnb read/write r/w r/w r/w r/w r/w r/w r r/w initial value00000 0 00 182 2570n?avr?05/11 atmega325/3250/645/6450 ? bit 2 ? ucszn2: character size the ucszn2 bits combined with the ucszn1:0 bit in ucsrnc sets the number of data bits (character size) in a frame the receiver and transmitter use. ? bit 1 ? rxb8n: receive data bit 8 rxb 8 n is the ninth data bit of the received charac ter when operating with serial frames with nine data bits. must be read before reading the low bits from udrn. ? bit 0 ? txb8n: transmit data bit 8 txb 8 n is the ninth data bit in the character to be transmitted when operating with serial frames with nine data bits. must be written before writing the low bits to udrn. 20.11.4 ucsrnc ? usart contro l and status register n c ? bit 6 ? umseln: usart mode select this bit selects between asynchronous and synchronous mode of operation. ? bit 5:4 ? upmn1:0: parity mode these bits enable and set type of parity generation and check. if enabled, the transmitter will automatically generate and send the parity of th e transmitted data bits within each frame. the receiver will generate a parity value for the in coming data and compare it to the upmn0 setting. if a mismatch is detected, the upen flag in ucsrna will be set. bit 7 6 5 4 3 2 1 0 ? umseln upmn1 upmn0 usbsn ucszn1 ucszn0 ucpoln ucsrnc read/write r r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 1 1 0 table 20-8. umsel bit settings umseln mode 0 asynchronous operation 1 synchronous operation table 20-9. upm bits settings upmn1 upmn0 parity mode 0 0 disabled 01reserved 1 0 enabled, even parity 1 1 enabled, odd parity 183 2570n?avr?05/11 atmega325/3250/645/6450 ? bit 3 ? usbsn: stop bit select this bit selects the number of stop bits to be inserted by the transmitter. the receiver ignores this setting. ? bit 2:1 ? ucszn1:0: character size the ucszn1:0 bits combined with the ucszn2 bit in ucsrnb sets the number of data bits (character size) in a frame the receiver and transmitter use. ? bit 0 ? ucpoln: clock polarity this bit is used for synchronous mode only. write this bit to zero when asynchronous mode is used. the ucpoln bit sets the relationship between data output change and data input sample, and the synchronous clock (xck). table 20-10. usbs bit settings usbsn stop bit(s) 01-bit 12-bit table 20-11. ucsz bits settings ucszn2 ucszn1 ucszn0 character size 0 0 0 5-bit 0 0 1 6-bit 0 1 0 7-bit 011 8 -bit 100reserved 101reserved 110reserved 1 1 1 9-bit table 20-12. ucpol bit settings ucpoln transmitted data changed (output of txd pin) received data sampled (input on rxd pin) 0 rising xck edge falling xck edge 1 falling xck edge rising xck edge 184 2570n?avr?05/11 atmega325/3250/645/6450 20.11.5 ubrrnl and ubrrnh ? usart baud rate registers ? bit 15:12 ? reserved bits these bits are reserved for future use. for compatibility with future devices, these bit must be written to zero when ubrrh is written. ? bit 11:0 ? ubrr11:0: usart baud rate register this is a 12-bit register which contains the usart baud rate. the ubrrh contains the four most significant bits, and the ubrrl contains th e eight least significant bits of the usart baud rate. ongoing transmis sions by the transmitter and receiver will be corrupted if the baud rate is changed. writing ubrrl will tr igger an immediate update of the baud rate prescaler. bit 151413121110 9 8 ? ? ? ? ubrrn[11:8] ubrrnh ubrrn[7:0] ubrrnl 76543210 read/write r r r r r/w r/w r/w r/w r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 00000000 185 2570n?avr?05/11 atmega325/3250/645/6450 21. usi ? universal serial interface the universal serial interface, or usi, provides the basic hardware resources needed for serial communication. combined with a minimum of cont rol software, the usi allows significantly higher transfer rates and uses less code space than solutions based on software only. interrupts are included to minimize the processor load. the main features of the usi are: ? two-wire synchronous data tr ansfer (master or slave) ? three-wire synchronous data transfer (master or slave) ? data received interrupt ? wake up from idle mode ? in two-wire mode: wake-up from all sleep modes, including power-down mode ? two-wire start condition detect or with interr upt capability 21.1 overview a simplified block diagram of the usi is shown on figure 21-1. for the actual placement of i/o pins, refer to ?pinout atmega3250/6450? on page 2 and ?pinout atmega325/645? on page 3 . cpu accessible i/o registers, including i/o bits and i/o pins, are shown in bold. the device- specific i/o register and bit locations are listed in the ?register descriptions? on page 192 . figure 21-1. universal serial interface, block diagram the 8 -bit shift register is directly accessible via the data bus and contains the incoming and outgoing data. the register has no buffering so the data must be read as quickly as possible to ensure that no data is lost. the most signific ant bit is connected to one of two output pins depending of the wire mode configuration. a transparent latch is inserted between the serial register output and output pin, which delays the change of data output to the opposite clock edge of the data input sampling. the serial input is always sampled from the data input (di) pin independent of the configuration. the 4-bit counter can be both read and written via the data bus, and can generate an overflow interrupt. both the serial register and the coun ter are clocked simultaneously by the same clock source. this allows the counter to count the number of bits received or transmitted and generate data bus usipf usitc usiclk usics0 usics1 usioif usioie usidc usisif usiwm0 usiwm1 usisie bit7 two-wire clock control unit do (output only) di/sda (input/open drain) usck/scl (input/open drain) 4-bit counter usidr usisr dq le usicr clock hold tim0 comp bit0 [1] 3 0 1 2 3 0 1 2 0 1 2 186 2570n?avr?05/11 atmega325/3250/645/6450 an interrupt when the transfer is complete. note that when an external clock source is selected the counter counts both clock edges. in this ca se the counter counts the number of edges, and not the number of bits. the clock can be selected from three different sources: the usck pin, timer/counter0 compare match or from software. the two-wire clock control unit can generate an interrupt when a start condition is detected on the two-wire bus. it can also generate wait states by holding the clock pin low after a start con- dition is detected, or after the counter overflows. 21.2 functional descriptions 21.2.1 three-wire mode the usi three-wire mode is compliant to the serial peripheral interface (spi) mode 0 and 1, but does not have the slave select (ss) pin functionality. however, this feature can be implemented in software if necessary. pin names used by this mode are: di, do, and usck. figure 21-2. three-wire mode operat ion, simplified diagram figure 21-2 shows two usi units operating in three-wire mode, one as master and one as slave. the two shift registers are interconnected in such way that after eight usck clocks, the data in each register are interchanged. the same clock also increments the usi?s 4-bit counter. the counter overflow (interrupt) flag, or us ioif, can therefore be used to determine when a transfer is completed. the clock is generated by the master device software by toggling the usck pin via the port register or by writing a one to the usitc bit in usicr. slave master bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0 do di usck bit7 bit6 bit5 bit4 bit3 bit2 bit1 bit0 do di usck portxn 187 2570n?avr?05/11 atmega325/3250/645/6450 figure 21-3. three-wire mode, timing diagram the three-wire mode timing is shown in figure 21 -3. at the top of the figure is a usck cycle ref- erence. one bit is shifted into the usi shift register (usidr) for each of these cycles. the usck timing is shown for both external clock mo des. in external clock mode 0 (usics0 = 0), di is sampled at positive edges, and do is changed (data register is shifted by one) at negative edges. external clock mode 1 (usics0 = 1) uses the opposite edges versus mode 0, i.e., sam- ples data at negative and changes the output at positive edges. the usi clock modes corresponds to the spi data mode 0 and 1. referring to the timing diagram (figure 21-3.), a bus transfer involves the following steps: 1. the slave device and master device sets up its data output and, depending on the proto- col used, enables its output driver (mark a and b). the output is set up by writing the data to be transmitted to the serial data register. enabling of the output is done by set- ting the corresponding bit in the port data direction register. note that point a and b does not have any specific order, but both must be at least one half usck cycle before point c where the data is sampled. this must be done to ensure that the data setup requirement is satisfied. the 4-bit counter is reset to zero. 2. the master generates a clock pulse by software toggling the usck line twice (c and d). the bit value on the slave and master?s data input (di) pin is sampled by the usi on the first edge (c), and the data output is changed on the opposite edge (d). the 4-bit counter will count both edges. 3. step 2. is repeated eight times for a complete register (byte) transfer. 4. after eight clock pulses (i.e., 16 clock edge s) the counter will overflow and indicate that the transfer is completed. the data bytes transferred must now be processed before a new transfer can be initiated. the overflow inte rrupt will wake up the processor if it is set to idle mode. depending of the protocol used the slave device can now set its output to high impedance. 21.2.2 spi master operation example the following code demonstrates how to use the usi module as a spi master: spitransfer: sts usidr,r16 ldi r16,(1< 191 2570n?avr?05/11 atmega325/3250/645/6450 1. the a start condition is generated by the master by forcing the sda low line while the scl line is high (a). sda can be forced low either by writing a zero to bit 7 of the shift register, or by setting the corresponding bit in the port register to zero. note that the data direction register bit must be set to one for the output to be enabled. the slave device?s start detector logic (figure 21-6.) detects the start condition and sets the usisif flag. the flag can generate an interrupt if necessary. 2. in addition, the star t detector will hold the scl line low after the master has forced an negative edge on this line (b). this allows the slave to wake up from sleep or complete its other tasks before setting up the shift register to receive the address. this is done by clearing the start condition flag and reset the counter. 3. the master set the first bit to be transferred and releases the scl line (c). the slave samples the data and shift it into the serial register at the positive edge of the scl clock. 4. after eight bits are transferred containing slave address and data direction (read or write), the slave counter overflows and the scl line is forced low (d). if the slave is not the one the master has addressed, it releases the scl line and waits for a new start condition. 5. if the slave is addressed it holds the sda line low during the acknowledgment cycle before holding the scl line low again (i.e., the counter register must be set to 14 before releasing scl at (d)). depending of the r/w bit the master or slave enables its output. if the bit is set, a master read operation is in progress (i.e., the slave drives the sda line) the slave can hold the scl line low after the acknowledge (e). 6. multiple bytes can now be transm itted, all in same direction, until a stop condition is given by the master (f). or a new start condition is given. if the slave is not able to receive more data it does not acknowledge the data byte it has last received. when the master does a read operation it must terminate the operation by force the acknowledge bit low after the last byte transmitted. figure 21-6. start condition detector, logic diagram 21.2.5 start condition detector the start condition detector is shown in figure 21-6. the sda line is delayed (in the range of 50 to 300 ns) to ensure valid sampling of the scl line. the start condition detector is only enabled in two-wire mode. the start condition detector is working asynchronously and can therefore wake up the processor from the power-down sleep mode. however, the protocol used might have restrictions on the scl hold time. therefore, when us ing this feature in this case th e oscillator start-up time set by the cksel fuses (see ?clock systems and their distribution? on page 26 ) must also be taken into the consideration. refer to the usisif bit description on page 193 for further details. 21.2.6 clock speed considerations. maximum frequency for scl and sck is f ck /4. this is also the maximum data transmit and receieve rate in both two- and three-wire mode. in two-wire slave mode the two-wire clock con- sda scl write( usisif) clock hold usisif dq clr dq clr 192 2570n?avr?05/11 atmega325/3250/645/6450 trol unit will hold the scl low unt il the slave is ready to receive more data. this may reduce the actual data rate in two-wire mode. 21.3 alternative usi usage when the usi unit is not used for serial communi cation, it can be set up to do alternative tasks due to its flexible design. 21.3.1 half-duplex asynchronous data transfer by utilizing the shift register in three-wire m ode, it is possible to implement a more compact and higher performance uart than by software only. 21.3.2 4-bit counter the 4-bit counter can be used as a stand-alone counter with overflow interrupt. note that if the counter is clocked externally, both clock edges will generate an increment. 21.3.3 12-bit timer/counter combining the usi 4-bit counter and timer/counter0 allows them to be used as a 12-bit counter. 21.3.4 edge triggered external interrupt by setting the counter to maximum value (f) it can function as an additional external interrupt. the overflow flag and interrupt enable bit are th en used for the external interrupt. this feature is selected by the usics1 bit. 21.3.5 software interrupt the counter overflow interrupt can be used as a software interrupt triggered by a clock strobe. 21.4 register descriptions 21.4.1 usidr ? usi data register the usi uses no buffering of the serial register, i.e., when accessing the data register (usidr) the serial register is accessed directly . if a serial clock occurs at the same cycle the register is written, the register will contain the valu e written and no shift is performed. a (left) shift operation is performed depending of the usics1..0 bits setting. the shift operation can be con- trolled by an external clock edge, by a timer/c ounter0 compare match, or directly by software using the usiclk strobe bit. note that even when no wire mode is selected (usiwm1..0 = 0) both the external data input (di/sda) and the external clock input (u sck/scl) can still be used by the shift register. the output pin in use, do or sda depending on the wire mode, is connected via the output latch to the most significant bit (bit 7) of the data register. the output latch is open (transparent) dur- ing the first half of a serial cloc k cycle when an external clock so urce is selected (usics1 = 1), and constantly open when an internal clock so urce is used (usics1 = 0). the output will be changed immediately when a new msb written as long as the latch is open. the latch ensures that data input is sampled and data output is changed on opposite clock edges. bit 7 6 5 4 3 2 1 0 (0xba) msb lsb usidr read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 193 2570n?avr?05/11 atmega325/3250/645/6450 note that the corresponding data direction register to the pin must be set to one for enabling data output from the shift register. 21.4.2 usisr ? usi status register the status register contains interrupt flags, line status flags and the counter value. ? bit 7 ? usisif: start condition interrupt flag when two-wire mode is selected, the usisif flag is set (to one) when a start condition is detected. when output disable mode or three-wire mode is selected, the flag is set when the 4- bit counter is incremented. an interrupt will be generated when the flag is set while th e usisie bit in usicr and the global interrupt enable flag are set. the flag will only be cleared by writing a logical one to the usisif bit. clearing this bit will release the start de tection hold of uscl in two-wire mode. a start condition interrupt will wake up the processor from all sleep modes. ? bit 6 ? usioif: counter overflow interrupt flag this flag is set (one) when the 4-bit counter overflows (i.e., at the transition from 15 to 0). an interrupt will be generate d when the flag is set while the usioie bit in usicr and the global interrupt enable flag ar e set. the flag will only be cleared if a one is written to the usioif bit. clearing this bit will release the counter overfl ow hold of scl in two-wire mode. a counter overflow interrupt will wake up the processor from idle sleep mode. ? bit 5 ? usipf: stop condition flag when two-wire mode is selected, the usipf flag is set (one) when a stop condition is detected. the flag is cleared by writing a one to this bit. note that this is not an interrupt flag. this signal is useful when implementing two-wire bus master arbitration. ? bit 4 ? usidc: data output collision this bit is logical one when bit 7 in the shift regi ster differs from the physical pin value. the flag is only valid when two-wire mode is used. this signal is useful when implementing two-wire bus master arbitration. ? bits 3:0 ? usicnt3:0: counter value these bits reflect the current 4-bit counter value. the 4-bit counter value can directly be read or written by the cpu. the 4-bit counter increments by one for each clock generated either by the external clock edge detector, by a timer/counter0 compare match, or by software using usiclk or usitc strobe bits. the clock source depends of the setting of the usics1..0 bits. for external clock operation a special feature is added that allows the clock to be generated by writing to the usitc strobe bit. this feature is enabled by write a one to the usiclk bit while setting an external clock source (usics1 = 1). note that even when no wire mode is selected (usiwm1..0 = 0) the external clock input (usck/scl) are can still be used by the counter. bit 76543 210 (0xb9) usisif usioif usipf usidc usicnt3 usicnt2 usicnt1 usicnt0 usisr read/write r/w r/w r/w r r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 194 2570n?avr?05/11 atmega325/3250/645/6450 21.4.3 usicr ? usi control register the control register includes interrupt enable control, wire mode setting, clock select setting, and clock strobe. ? bit 7 ? usisie: start condition interrupt enable setting this bit to one enables the start condition detector interrupt. if there is a pending inter- rupt when the usisie and the globa l interrupt enable flag is set to one, this will immediately be executed. refer to the usisif bit description on page 193 for further details. ? bit 6 ? usioie: counter overflow interrupt enable setting this bit to one enables the counter overflow interrupt. if there is a pending interrupt when the usioie and the global interrupt enable flag is set to one, this will immediately be executed. refer to the usioif bit description on page 193 for further details. ? bit 5:4 ? usiwm1:0: wire mode these bits set the type of wire mode to be us ed. basically only the function of the outputs are affected by these bits. data and clock inputs are not affected by the mode selected and will always have the same function. the counter and shift register can therefore be clocked exter- nally, and data input sampled, even when outputs are disabled. the relations between usiwm1:0 and the usi operation is summarized in table 21-1 . bit 7 6 5 4 3 2 1 0 (0xb 8 ) usisie usioie usiwm1 usiwm0 us ics1 usics0 usiclk usitc usicr read/write r/w r/w r/w r/w r/w r/w w w initial value 0 0 0 0 0 0 0 0 195 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. the di and usck pins are renamed to serial data (sda) and serial clock (scl) respectively to avoid confusion between the modes of operation. table 21-1. relations between usiwm1..0 and the usi operation usiwm1 usiwm0 description 0 0 outputs, clock hold, and start detect or disabled. port pins operates as normal. 0 1 three-wire mode. uses do, di, and usck pins. the data output (do) pin overrides the corresponding bit in the port register in this mode. however, the corresponding ddr bit still controls the data direction. when the port pin is set as input the pins pull-up is controlled by the port bit. the data input (di) and serial clock (usck) pins do not affect the normal port operation. when operating as master, clock pulses are software generated by toggling the port register, while the data direction is set to output. the usit c bit in the usicr register can be used for this purpose. 1 0 two-wire mode. uses sda (di) and scl (usck) pins (1) . the serial data (sda) and the serial clock (scl) pins are bi- directional and uses open-collector output drives. the output drivers are enabled by setting the corresponding bit for sda and scl in the ddr register. when the output driver is enabled fo r the sda pin, the output driver will force the line sda low if the outpu t of the shift register or the corresponding bit in the port register is zero. otherwise the sda line will not be driven (i.e., it is released). when the scl pin output driver is enabled the scl line will be forced low if the corresponding bit in the port register is zero, or by the start detector. otherwise the scl line will not be driven. the scl line is held low when a start detector detects a start condition and the output is enabled. clearing the start condition flag (usisif) releases the line. the sda and scl pin inputs is not affected by enabling this mode. pull-ups on the sda and scl port pin are disabled in two-wire mode. 1 1 two-wire mode. uses sda and scl pins. same operation as for the two-wire mode described above, except that the scl line is also held low when a counter overflow occurs, and is held low until the counter overflow flag (usioif) is cleared. 196 2570n?avr?05/11 atmega325/3250/645/6450 ? bit 3:2 ? usics1:0: clock source select these bits set the clock source for the shift register and counter. the data output latch ensures that the output is changed at the opposite edge of the sampling of the data input (di/sda) when using external clock source (usck/scl). when software strobe or timer/counter0 compare match clock option is selected, the output latch is transparent and therefore the output is changed immediately. clearing the usics1..0 bits enables software strobe option. when using this option, writing a one to the usiclk bit clocks both the shift register and the counter. for external clock source (usics1 = 1), the usiclk bit is no longer used as a strobe, but selects between external clocking and software clocking by the usitc strobe bit. table 21-2 shows the relationship between the usic s1..0 and usiclk setting and clock source used for the shift register and the 4-bit counter. ? bit 1 ? usiclk: clock strobe writing a one to this bit location strobes the sh ift register to shift one step and the counter to increment by one, provided that the usics1..0 bits are set to zero and by doing so the software clock strobe option is selected. the output will change immediately when the clock strobe is exe- cuted, i.e., in the same instruction cycle. the va lue shifted into the shift register is sampled the previous instruction cycle. the bit will be read as zero. when an external clock source is selected (usics1 = 1), the usiclk function is changed from a clock strobe to a clock select register. setting the usiclk bit in this case will select the usitc strobe bit as clock sour ce for the 4-bit counter (see table 21-2 ). ? bit 0 ? usitc: toggle clock port pin writing a one to this bit location toggles the usck/s cl value either from 0 to 1, or from 1 to 0. the toggling is independent of the setting in the data direction register, but if the port value is to be shown on the pin the ddre4 must be set as output (to one). this feature allows easy clock generation when implementi ng master devices. the bit will be read as zero. when an external clock source is selected (usics1 = 1) and the usiclk bit is set to one, writ- ing to the usitc strobe bit will directly clock the 4- bit counter. this allows an early detection of when the transfer is done when operating as a master device. table 21-2. relations between the usics1..0 and usiclk setting usics1 usics0 usiclk shift register clock source 4-bit counter clock source 0 0 0 no clock no clock 0 0 1 software clock strobe (usiclk) software clock strobe (usiclk) 0 1 x timer/counter0 compare match timer/counter0 compare match 1 0 0 external, positive edge external, both edges 1 1 0 external, negative edge external, both edges 1 0 1 external, positive edge software clock strobe (usitc) 1 1 1 external, negative edge software clock strobe (usitc) 197 2570n?avr?05/11 atmega325/3250/645/6450 22. analog comparator the analog comparator compares the input values on the positive pin ain0 and negative pin ain1. when the voltage on the positive pin ain0 is higher than the voltage on the negative pin ain1, the analog comparator output, aco, is set. the comparator?s output can be set to trigger the timer/counter1 input capture function. in addition, the comparator can trigger a separate interrupt, exclusive to the analog comparator. th e user can select interrupt triggering on com- parator output rise, fall or toggle. a block diagram of the comparator and its surrounding logic is shown in figure 22-1 . the power reduction adc bit, pradc, in ?power reduction register? on page 37 must be dis- abled by writing a logical zero to be able to use the adc module. figure 22-1. analog comparator block diagram (2) notes: 1. see table 22-1 on page 19 8 . 2. refer to figure 1-1 on page 2 , figure 1-2 on page 3 , and ?alternate functions of port e? on page 72 for analog comparator pin placement. acbg bandgap reference adc multiplexer output acme aden (1) 198 2570n?avr?05/11 atmega325/3250/645/6450 22.1 analog comparator multiplexed input it is possible to select any of the adc7..0 pins to replace the negative input to the analog com- parator. the adc multiplexer is used to select this input, and consequently, the adc must be switched off to utilize this feature. if the analog comparator multiplexer enable bit (acme in adcsrb) is set and the adc is switched off (a den in adcsra is zero), mux2..0 in admux select the input pin to replace the negative input to the analog comparator, as shown in table 22-1 . if acme is cleared or aden is set, ain1 is applied to the negative input to the analog comparator. 22.2 register description 22.2.1 adcsrb ? adc control and status register b ? bit 6 ? acme: analog comparator multiplexer enable when this bit is written logic one and the adc is switched off (aden in adcsra is zero), the adc multiplexer selects the negative input to the analog comparator. when this bit is written logic zero, ain1 is applied to the negative input of the analog comparator. for a detailed description of this bit, see ?didr1 ? digital input disable register 1? on page 200 . 22.2.2 acsr ? analog comparator control and status register table 22-1. analog comparator multiplexed input acme aden mux2..0 analog comparator negative input 0 x xxx ain1 1 1 xxx ain1 1 0 000 adc0 1 0 001 adc1 1 0 010 adc2 1 0 011 adc3 1 0 100 adc4 1 0 101 adc5 1 0 110 adc6 1 0 111 adc7 bit 7 6543210 (0x7b) ? acme ? ? ? adts2 adts1 adts0 adcsrb read/write r r/w r r r r/w r/w r/w initial value0 0000000 bit 76543210 0x30 (0x50) acd acbg aco aci acie acic acis1 acis0 acsr read/write r/w r/w r r/w r/w r/w r/w r/w initial value00n/a00000 199 2570n?avr?05/11 atmega325/3250/645/6450 ? bit 7 ? acd: analog comparator disable when this bit is written logic one , the power to the analog comparator is switched off. this bit can be set at any time to tu rn off the analog com parator. this will reduce power consumption in active and idle mode. when changing the acd bit, the analog comparator interrupt must be disabled by clearing the acie bit in acsr. otherwise an interrupt can occur when the bit is changed. ? bit 6 ? acbg: analog comparator bandgap select when this bit is set, a fixed bandgap reference vo ltage replaces the positive input to the analog comparator. when this bit is cleared, ain0 is ap plied to the positive input of the analog compar- ator. when the bandgap reference is used as input to the analog comparator, it will take a certain time for the volt age to stabilize. if not stabilized, the the first converison may give a wrong value. see ?internal voltage reference? on page 44. ? bit 5 ? aco: analog comparator output the output of the analog comparator is synchronized and then directly connected to aco. the synchronization introduces a delay of 1 - 2 clock cycles. ? bit 4 ? aci: analog comparator interrupt flag this bit is set by hardware when a comparator output event triggers the interrupt mode defined by acis1 and acis0. the analog comparator interr upt routine is executed if the acie bit is set and the i-bit in sreg is set. aci is cleared by hardware when executing the corresponding inter- rupt handling vector. alternatively, aci is cleared by writing a logic one to the flag. ? bit 3 ? acie: analog comparator interrupt enable when the acie bit is written logic one and the i-bi t in the status register is set, the analog com- parator interrupt is activated. when written logic zero, the interrupt is disabled. ? bit 2 ? acic: analog comparator input capture enable when written logic one, this bit enables the input capture function in timer/counter1 to be trig- gered by the analog comparator. the comparator output is in this case directly connected to the input capture front-end logic, making the comp arator utilize the noise canceler and edge select features of the timer/counter1 input capture interrupt. when written logic zero, no connection between the analog comparator and the input capture function exists. to make the comparator trigger the timer/counter1 input capture interrupt, the icie1 bit in the timer interrupt mask register (timsk1) must be set. 200 2570n?avr?05/11 atmega325/3250/645/6450 ? bits 1, 0 ? acis1, acis0: analog comparator interrupt mode select these bits determine which comparator events that trigger the analog comparator interrupt. the different settings are shown in table 22-2 . when changing the acis1/acis0 bits, the analog comparator interrupt must be disabled by clearing its interrupt enable bit in the acsr register. otherwise an interrupt can occur when the bits are changed. 22.2.3 didr1 ? digital in put disable register 1 ? bit 1, 0 ? ain1d, ain0d: ai n1, ain0 digita l input disable when this bit is written logic one, the digital input buffer on the ain1/0 pin is disabled. the corre- sponding pin register bit will alwa ys read as zero when this bit is set. when an analog signal is applied to the ain1/0 pin and the digital input from this pin is not needed, this bit should be writ- ten logic one to reduce power consumption in the digital input buffer. table 22-2. acis1/acis0 settings acis1 acis0 interrupt mode 0 0 comparator interrupt on output toggle. 01reserved 1 0 comparator interrupt on falling output edge. 1 1 comparator interrupt on rising output edge. bit 76543210 (0x7f) ? ? ? ? ? ? ain1d ain0d didr1 read/writerrrrrrr/wr/w initial value00000000 201 2570n?avr?05/11 atmega325/3250/645/6450 23. analog to digital converter 23.1 features ? 10-bit resolution ? 0.5 lsb integral non-linearity ? 2 lsb absolute accuracy ? 13s - 260s conversion time (50khz to 1mhz adc clock) ? up to 76.9ksps at maximum re solution (200khz adc clock) ? eight multiplexed single ended input channels ? optional left adjustment for adc result readout ? 0 - v cc adc input voltage range ? selectable 1.1v adc reference voltage ? free running or single conversion mode ? adc start conversion by auto tr iggering on interrupt sources ? interrupt on adc conversion complete ? sleep mode no ise canceler the atmel atmega325/3250/645/6450 features a 10-bit successive approximation adc. the adc is connected to an 8 -channel analog multiplexer which allows eight single-ended voltage inputs constructed from the pins of port f. th e single-ended voltage inputs refer to 0v (gnd). the adc contains a sample and hold circuit whic h ensures that the input voltage to the adc is held at a constant level during conversion . a block diagram of the adc is shown in figure 23-1 . the adc has a separate analog supply voltage pin, avcc. av cc must not differ more than 0.3v from v cc . see the paragraph ?adc noise canceler? on page 207 on how to connect this pin. internal reference voltages of nominally 1.1v or avcc are provided on-chip. the voltage refer- ence may be externally decoupled at the aref pi n by a capacitor for better noise performance. the power reduction adc bit, pradc, in ?power reduction register? on page 37 must be dis- abled by writing a logical zero to be able to use the adc module. 202 2570n?avr?05/11 atmega325/3250/645/6450 figure 23-1. analog to digital converter block schematic 23.2 operation the adc converts an analog input voltage to a 10-bit digital value through successive approxi- mation. the minimum value represents gnd and the maximum value represents the voltage on the aref pin minus 1 lsb. optionally, avcc or an internal 1.1v reference voltage may be con- nected to the aref pin by writing to the refsn bits in the admux register. the internal voltage reference may thus be decoupled by an external capacitor at the aref pin to improve noise immunity. the analog input channel is selected by writing to the mux bits in admux. any of the adc input pins, as well as gnd and a fixed bandgap voltage reference, can be selected as single ended inputs to the adc. the adc is enabled by sett ing the adc enable bit, aden in adcsra. volt- age reference and input channel se lections will not go into effect until aden is set. the adc does not consume power when aden is cleared, so it is recommended to switch off the adc before entering power saving sleep modes. the adc generates a 10-bit result which is pr esented in the adc data registers, adch and adcl. by default, the result is presented right adjusted, but can optionally be presented left adjusted by setting the adlar bit in admux. adc conversion complete irq 8-bit data bus 15 0 adc multiplexer select (admux) adc ctrl. & status register (adcsra) adc data register (adch/adcl) mux2 adie adate adsc aden adif adif mux1 mux0 adps0 adps1 adps2 mux3 conversion logic 10-bit dac + - sample & hold comparator internal reference mux decoder mux4 avcc adc7 adc6 adc5 adc4 adc3 adc2 adc1 adc0 refs0 refs1 adlar + - channel selection gain selection adc[ 9 :0] adc multiplexer output differential amplifier aref bandgap reference prescaler single ended / differential selection gnd pos. input mux neg. input mux trigger select adts[2:0] interrupt flags start 203 2570n?avr?05/11 atmega325/3250/645/6450 if the result is left adjusted and no more than 8 -bit precision is required, it is sufficient to read adch. otherwise, adcl must be read first, then adch, to ensure that the content of the data registers belongs to the same conversion. once adcl is read, adc access to data registers is blocked. this means that if adcl has been read, and a conversion completes before adch is read, neither register is updated and the result fr om the conversion is lost. when adch is read, adc access to the adch and ad cl registers is re-enabled. the adc has its own interrupt which can be triggered when a conversion completes. when adc access to the data registers is prohibited between reading of adch and adcl, the interrupt will trigger even if the result is lost. 23.3 starting a conversion a single conversion is started by writing a l ogical one to the adc start conversion bit, adsc. this bit stays high as long as the conversi on is in progress and will be cleared by hardware when the conversion is completed. if a different data channel is selected while a conversion is in progress, the adc will finish the current conv ersion before performing the channel change. alternatively, a conversion can be triggered automatically by various sources. auto triggering is enabled by setting the adc auto trigger enable bi t, adate in adcsra. the trigger source is selected by setting the adc trig ger select bits, adts in adcsrb (see description of the adts bits for a list of the trigger sources). when a positive edge occurs on the selected trigger signal, the adc prescaler is reset and a conversion is st arted. this provides a method of starting con- versions at fixed intervals. if the trigger signal still is set when the conversion completes, a new conversion will not be star ted. if another positive edge occurs on the trigger si gnal during con- version, the edge will be ignored. note that an interrupt flag will be set even if the specific interrupt is disabled or the global interrupt enable bit in sreg is cleared. a conversion can thus be triggered without causing an interrupt. however, the interrupt flag must be cleared in order to trigger a new conversion at the next interrupt event. figure 23-2. adc auto trigger logic using the adc interrupt flag as a trigger source makes the adc start a new conversion as soon as the ongoing conversion has finished. the adc then operates in free running mode, con- stantly sampling and updating the adc data register. the first conversion must be started by writing a logical one to the adsc bit in adcs ra. in this mode the adc will perform successive conversions independently of whether the a dc interrupt flag, adif is cleared or not. adsc adif source 1 source n adts[2:0] conversion logic prescaler start clk adc . . . . edge detector adate 204 2570n?avr?05/11 atmega325/3250/645/6450 if auto triggering is enabled, single conversi ons can be started by writing adsc in adcsra to one. adsc can also be used to determine if a conversion is in progress. the adsc bit will be read as one during a conversion, independently of how the conversion was started. 23.4 prescaling and conversion timing figure 23-3. adc prescaler by default, the successive approximation circ uitry requires an input clock frequency between 50khz and 200khz to get maximum resolution. if a lower resolution than 10 bits is needed, the input clock frequency to the adc can be higher than 200khz to get a higher sample rate. the adc module contains a prescaler, which generates an acceptable adc clock frequency from any cpu frequency above 100khz. the prescaling is set by the adps bits in adcsra. the prescaler starts counting from the moment the adc is switched on by setting the aden bit in adcsra. the prescaler keeps running for as lo ng as the aden bit is set, and is continuously reset when aden is low. when initiating a single ended conversion by se tting the adsc bit in adcsra, the conversion starts at the following rising edge of the adc clock cycle. a normal conversion takes 13 adc clock cycles. the first conversion after the adc is switched on (aden in adcsra is set) takes 25 adc clock cycles in order to initialize the analog circuitry. when the bandgap reference voltage is used as input to the adc, it will take a certain time for the voltage to stabilize. if not stabilized the first value read after the first conversion may be wrong. the actual sample-and-hold takes place 1.5 adc clock cycles after the start of a normal conver- sion and 13.5 adc clock cycles after the start of an first conv ersion. when a conversion is complete, the result is written to the adc data re gisters, and adif is set. in single conversion mode, adsc is cleared simultaneously. the software may then set adsc again, and a new conversion will be init iated on the first rising adc clock edge. when auto triggering is used, the prescaler is reset when the trigger event occurs. this assures a fixed delay from the trigger event to the start of conversion. in this mode, the sample-and-hold takes place two adc clock cycles after the rising edge on the trigger source signal. three addi- tional cpu clock cycles are used for synchronization logic. when using differential mode, along 7-bit adc prescaler adc clock source ck adps0 adps1 adps2 ck/128 ck/2 ck/4 ck/8 ck/16 ck/32 ck/64 reset aden start 205 2570n?avr?05/11 atmega325/3250/645/6450 with auto triggering from a source other than the adc conversion complete, each conversion will require 25 adc clocks. this is because the adc must be disabled and re-enabled after every conversion. in free running mode, a new conversion will be started immediately after the conversion com- pletes, while adsc remains high. for a summary of conversion times, see table 23-1 . figure 23-4. adc timing diagram, first conver sion (single conversion mode) figure 23-5. adc timing diagram, single conversion figure 23-6. adc timing diagram, auto triggered conversion sign and msb of result lsb of result adc clock adsc sample & hold adif adch adcl cycle number aden 1 212 13 14 15 16 17 18 1 9 20 21 22 23 24 25 1 2 first conversion next conversion 3 mux and refs update mux and refs update conversion complete 1 2 3 4 5 6 7 8 9 10 11 12 13 sign and msb of result lsb of result adc clock adsc adif adch adcl cycle number 12 one conversion next conversion 3 sample & hold mux and refs update conversion complete mux and refs update 1 2 3 4 5 6 7 8 9 10 11 12 13 sign and msb of result lsb of result adc clock trigger source adif adch adcl cycle number 12 one conversion next conversion conversion complete prescaler reset adate prescaler reset sample & hold mux and refs update 206 2570n?avr?05/11 atmega325/3250/645/6450 figure 23-7. adc timing diagram, free running conversion 23.5 changing channel or reference selection the muxn and refs1:0 bits in the admux register are single buffered through a temporary register to which the cpu has random access. this ensures that the channels and reference selection only takes place at a safe point dur ing the conversion. the channel and reference selection is continuously updated until a conversion is started. once the conversion starts, the channel and reference selection is locked to ensure a sufficient sampling time for the adc. con- tinuous updating resumes in the last adc clock cycle before the conversion completes (adif in adcsra is set). note that the conversion star ts on the following rising adc clock edge after adsc is written. the user is thus advised not to write new channel or reference selection values to admux until one adc clock cycle after adsc is written. if auto triggering is used, the exact time of t he triggering event can be indeterministic. special care must be taken when updating the admux register, in order to control which conversion will be affected by the new settings. if both adate and aden is written to one, an interrupt event can occur at any time. if the admux register is changed in this period, the user cannot tell if the next conversion is based on the old or the new settings. admux can be safely updated in the following ways: 1. when adate or aden is cleared. 2. during conversion, minimum one adc clock cycle after the trigger event. 3. after a conversion, before the interrupt flag used as trigger source is cleared. when updating admux in one of these conditions, the new settings will affect the next adc conversion. table 23-1. adc conversion time condition sample & hold (cycles from start of conversion) conversion time (cycles) first conversion 13.5 25 normal conversions, single ended 1.5 13 auto triggered conversions 2 13.5 11 12 13 sign and msb of result lsb of result adc clock adsc adif adch adcl cycle number 12 one conversion next conversion 34 conversion complete sample & hold mux and refs update 207 2570n?avr?05/11 atmega325/3250/645/6450 23.5.1 adc input channels when changing channel selections, the user should observe the following guidelines to ensure that the correct channel is selected: in single conversion mode, always select the channel before starting the conversion. the chan- nel selection may be changed one adc clock cycle after writing one to adsc. however, the simplest method is to wait for the conversion to complete before changing the channel selection. in free running mode, always select the channel before starting the first conversion. the chan- nel selection may be changed one adc clock cycle after writing one to adsc. however, the simplest method is to wait for the first conversion to complete, and then change the channel selection. since the next conver sion has already started automati cally, the next result will reflect the previous channel selection. subsequent conversions will refl ect the new channel selection. 23.5.2 adc voltage reference the reference voltage for the adc (v ref ) indicates the conversion range for the adc. single ended channels that exceed v ref will result in code s close to 0x3ff. v ref can be selected as either avcc, internal 1.1v reference, or external aref pin. avcc is connected to the adc through a passive switch. the internal 1.1v reference is gener- ated from the internal bandgap reference (v bg ) through an internal buffer. in either case, the external aref pin is directly connected to the adc, and the reference voltage can be made more immune to noise by connecting a capacitor between the aref pin and ground. v ref can also be measured at the aref pin with a high impedant voltmeter. note that v ref is a high impedant source, and only a capacitive load should be connected in a system. if the user has a fixed voltage source connected to the aref pin, the user may not use the other reference voltage options in the ap plication, as they will be shorte d to the external voltage. if no external voltage is applied to the aref pin, the user may switch between avcc and 1.1v as reference selection. the first adc conversion result after switching reference voltage source may be inaccurate, and the user is advised to discard this result. 23.6 adc noise canceler the adc features a noise canceler that enables conversion during sleep mode to reduce noise induced from the cpu core and other i/o peripherals. the noise canceler can be used with adc noise reduction and idle mode. to make use of this feature, the following procedure should be used: 1. make sure that the adc is enabled and is not busy converting. single conversion mode must be selected and the adc conversion complete interrupt must be enabled. 2. enter adc noise reduction mode (or id le mode). the adc will start a conversion once the cpu has been halted. 3. if no other interrupts occur before the adc conversion completes, the adc interrupt will wake up the cpu and execute the adc conv ersion complete in terrupt routine. if another interrupt wakes up the cpu before the adc conversion is complete, that interrupt will be executed, and an adc conv ersion complete interrupt request will be generated when the adc conversion comple tes. the cpu will remain in active mode until a new sleep command is executed. note that the adc will not be automatically turned off when entering other sleep modes than idle mode and adc noise reduction mode. the user is advised to write zero to aden before enter- ing such sleep modes to avoid excessive power consumption. 208 2570n?avr?05/11 atmega325/3250/645/6450 23.6.1 analog input circuitry the analog input circuitry for single ended channels is illustrated in figure 23- 8 . an analog source applied to adcn is subjected to the pin capacitance and input leakage of that pin, regard- less of whether that channel is selected as input for the adc. when the channel is selected, the source must drive the s/h capacitor through the series resistance (combined resistance in the input path). the adc is optimized for analog signals wit h an output impedance of approximately 10 k or less. if such a source is used, the sampling time will be negligible. if a source with higher imped- ance is used, the sampling time will depend on how long time the source nee ds to charge the s/h capacitor, with can vary widely. the user is recommended to only use low impedant sources with slowly varying signals, since this minimizes the required charge transfer to the s/h capacitor. signal components higher than the nyquist frequency (f adc /2) should not be present for either kind of channels, to avoid distortion from unpredictable signal convolution. the user is advised to remove high frequency components with a low-pass filter before applying the signals as inputs to the adc. figure 23-8. analog input circuitry 23.6.2 analog noise canceling techniques digital circuitry inside and outside the device ge nerates emi which might affect the accuracy of analog measurements. if conversion accuracy is critical, the noise level can be reduced by applying the following techniques: 1. keep analog signal paths as short as possible. make sure analog tracks run over the analog ground plane, and keep them well away from high-speed switching digital tracks. 2. the avcc pin on the device should be connected to the digital v cc supply voltage via an lc network as shown in figure 23-9 . 3. use the adc noise canceler function to reduce induced noise from the cpu. 4. if any adc port pins are used as digital outputs, it is essential that these do not switch while a conversion is in progress. adcn i ih 1..100 k c s/h = 14 pf v cc /2 i il 209 2570n?avr?05/11 atmega325/3250/645/6450 figure 23-9. adc power connections 23.6.3 adc accuracy definitions an n-bit single-ended adc converts a voltage linearly between gnd and v ref in 2 n steps (lsbs). the lowest code is read as 0, and the highest code is read as 2 n -1. several parameters describe the deviation from the ideal behavior: ? offset: the deviation of the first transition (0x000 to 0x001) compared to the ideal transition (at 0.5 lsb). ideal value: 0 lsb. figure 23-10. offset error vcc 100nf analog ground plane (adc0) pf0 (adc7) pf7 (adc1) pf1 (adc2) pf2 (adc3) pf3 (adc4) pf4 (adc5) pf5 (adc6) pf6 aref gnd avcc 52 53 54 55 56 57 5 8 59 60 61 61 62 62 63 63 64 64 1 51 dnc pa0 10 ? gnd output code v ref input voltage ideal adc actual adc offset error 210 2570n?avr?05/11 atmega325/3250/645/6450 ? gain error: after adjusting for offset, the gain error is found as the deviation of the last transition (0x3fe to 0x3ff) compared to the ideal transition (at 1.5 lsb below maximum). ideal value: 0 lsb figure 23-11. gain error ? integral non-linearity (inl): afte r adjusting for offset and gain error, the inl is the maximum deviation of an actual transition compared to an ideal transition for any code. ideal value: 0 lsb. figure 23-12. integral non-linearity (inl) output code v ref input voltage ideal adc actual adc gain error output code v ref input voltage ideal adc actual adc inl 211 2570n?avr?05/11 atmega325/3250/645/6450 ? differential non-linearity (dnl ): the maximum deviation of the actual code width (the interval between two adjacent transitions) from the ideal code width (1 lsb). ideal value: 0 lsb. figure 23-13. differential non-linearity (dnl) ? quantization error: due to the quantization of the input voltage into a finite number of codes, a range of input voltages (1 lsb wide) will code to the same value. always 0.5 lsb. ? absolute accuracy: the maximum deviation of an actual (unadjusted) transition compared to an ideal transition for any code. this is the compound effect of offset, gain error, differential error, non-linearity, and quantization error. ideal value: 0.5 lsb. 23.7 adc conversion result after the conversion is complete (adif is high ), the conversion result can be found in the adc result registers (adcl, adch). for single ended conversion, the result is where v in is the voltage on the selected input pin and v ref the selected voltage reference (see table 23-3 on page 213 and table 23-4 on page 214 ). 0x000 represents analog ground, and 0x3ff represents the selected reference voltage minus one lsb. output code 0x3ff 0x000 0 v ref input voltage dnl 1 lsb adc v in 1024 ? v ref -------------------------- = adc v pos v neg ? () 512 ? v ref ---------------------------------------------------- - = 212 2570n?avr?05/11 atmega325/3250/645/6450 figure 23-14. differential measurement range admux = 0xfb (adc3 - adc2, 1.1v reference, left adjusted result) voltage on adc3 is 300 mv, voltage on adc2 is 500 mv. adcr = 512 * (300 - 500) / 1100 = -93 = 0x3a3 . adcl will thus read 0xc0 , and adch will read 0xd 8 . writing zero to adlar right adjusts the result: adcl = 0xa3, adch = 0x03. table 23-2. correlation between input voltage and output codes v adcn read code corresponding decimal value v adcm + v ref 0x1ff 511 v adcm + 511 / 512 v ref 0x1ff 511 v adcm + 510 / 512 v ref 0x1fe 510 ... ... ... v adcm + 1 / 512 v ref 0x001 1 v adcm 0x000 0 v adcm - 1 / 512 v ref 0x3ff -1 ... ... ... v adcm - 511 / 512 v ref 0x201 -511 v adcm - v ref 0x200 -512 0 output code 0x1ff 0x000 v ref differential input voltage (volts) 0x3ff 0x200 - v ref 213 2570n?avr?05/11 atmega325/3250/645/6450 23.8 register description 23.8.1 admux ? adc multiplexer selection register ? bit 7:6 ? refs1:0: reference selection bits these bits select the voltage reference for the adc, as shown in table 23-3 . if these bits are changed during a conversion, the change will not go in effect until this conversion is complete (adif in adcsra is set). the internal voltage reference options may not be used if an external reference voltage is being applied to the aref pin. ? bit 5 ? adlar: adc left adjust result the adlar bit affects the presentation of the adc conversion result in the adc data register. write one to adlar to left adjust the result. otherwise, the result is right adjusted. changing the adlar bit will affect t he adc data register immediately, regardless of any ongoing conver- sions. for a complete description of this bit, see ?adcl and adch ? the adc data register? on page 216 . ? bits 4:0 ? mux4:0: analog channel selection bits the value of these bits selects which combination of analog inputs are connected to the adc. see table 23-4 for details. if these bits are changed during a conversion, the change will not go in effect until this conversion is complete (adif in adcsra is set). bit 76543210 (0x7c) refs1 refs0 adlar mux4 mux3 mux2 mux1 mux0 admux read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 table 23-3. voltage reference selections for adc refs1 refs0 voltage reference selection 0 0 aref, internal vref turned off 0 1 avcc with external capacitor at aref pin 10reserved 1 1 internal 1.1v voltage reference with external capacitor at aref pin 214 2570n?avr?05/11 atmega325/3250/645/6450 table 23-4. input channel selections mux4..0 single ended input positive differen tial input negative differential input 00000 adc0 n/a 00001 adc1 00010 adc2 00011 adc3 00100 adc4 00101 adc5 00110 adc6 00111 adc7 01000 01001 01010 01011 01100 01101 01110 01111 10000 adc0 adc1 10001 adc1 adc1 10010 n/a adc2 adc1 10011 adc3 adc1 10100 adc4 adc1 10101 adc5 adc1 10110 adc6 adc1 10111 adc7 adc1 11000 adc0 adc2 11001 adc1 adc2 11010 adc2 adc2 11011 adc3 adc2 11100 adc4 adc2 11101 adc5 adc2 11110 1.1v (v bg ) n/a 11111 0v (gnd) 215 2570n?avr?05/11 atmega325/3250/645/6450 23.8.2 adcsra ? adc control and status register a ? bit 7 ? aden: adc enable writing this bit to one enables the adc. by writi ng it to zero, the adc is turned off. turning the adc off while a conversion is in prog ress, will terminate this conversion. ? bit 6 ? adsc: adc start conversion in single conversion mode, write this bit to one to start each conversion. in free running mode, write this bit to one to start the first conversion. the first conversion after adsc has been written after the adc has been enabled, or if adsc is written at the same time as the adc is enabled, will take 25 adc clock cycles instead of the norma l 13. this first conversi on performs initializa- tion of the adc. adsc will read as one as long as a conversion is in progress. when the co nversion is complete, it returns to zero. writing zero to this bit has no effect. ? bit 5 ? adate: adc auto trigger enable when this bit is written to on e, auto triggering of the adc is enabled. the adc will start a con- version on a positive edge of the selected trigger signal. the trigger source is selected by setting the adc trigger select bits, adts in adcsrb. ? bit 4 ? adif: adc interrupt flag this bit is set when an adc conversion completes and the data registers are updated. the adc conversion complete interrupt is executed if the adie bit and the i-bit in sreg are set. adif is cleared by hardware when executing th e corresponding interrupt handling vector. alter- natively, adif is cleared by writing a logical one to the flag. beware that if doing a read-modify- write on adcsra, a pending interrupt can be dis abled. this also applies if the sbi and cbi instructions are used. ? bit 3 ? adie: adc interrupt enable when this bit is written to one and the i-bit in sreg is set, the adc conversion complete inter- rupt is activated. bit 76543210 (0x7a) aden adsc adate adif adie adps2 adps1 adps0 adcsra read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 216 2570n?avr?05/11 atmega325/3250/645/6450 ? bits 2:0 ? adps2:0: adc prescaler select bits these bits determine the division factor between the xtal frequency and the input clock to the adc. 23.8.3 adcl and adch ? the adc data register adlar = 0 adlar = 1 when an adc conversion is complete, the result is found in these two registers. when adcl is read, the adc data register is not updated until adch is read. consequently, if the result is left adjusted and no more than 8 -bit precision is required, it is sufficient to read adch. otherwise, adcl must be read first, then adch. the adlar bit in admux, and the muxn bits in admux affect the way the result is read from the registers. if adlar is set, the result is left adjusted. if adla r is cleared (default), the result is right adjusted. table 23-5. adc prescaler selections adps2 adps1 adps0 division factor 000 2 001 2 010 4 011 8 100 16 101 32 110 64 111 12 8 bit 151413121110 9 8 (0x79) ? ? ? ? ? ? adc9 adc8 adch (0x7 8 ) adc7 adc6 adc5 adc4 adc3 adc2 adc1 adc0 adcl 76543210 read/writerrrrrrrr rrrrrrrr initial value00000000 00000000 bit 151413121110 9 8 (0x79) adc9 adc8 adc7 adc6 adc5 adc4 adc3 adc2 adch (0x7 8 ) adc1 adc0 ? ????? adcl 76543210 read/writerrrrrrrr rrrrrrrr initial value00000000 00000000 217 2570n?avr?05/11 atmega325/3250/645/6450 ? adc9:0: adc conversion result these bits represent the result from the conversion, as detailed in ?adc conversion result? on page 211 . 23.8.4 adcsrb ? adc control and status register b ? bit 7 ? reserved bit this bit is reserved for future use. to ensure co mpatibility with future de vices, this bit must be written to zero when adcsrb is written. ? bit 2:0 ? adts2:0: adc auto trigger source if adate in adcsra is written to one, the value of these bits selects which source will trigger an adc conversion. if adate is cleared, the adts2:0 settings will have no effect. a conversion will be triggered by the risi ng edge of the selected interrupt flag . note that switch ing from a trig- ger source that is cleared to a trigger source that is set, will generate a positive edge on the trigger signal. if aden in adcsra is set, this will start a conversion. switching to free running mode (adts[2:0]=0) will not cause a trigger event, even if t he adc interrupt flag is set . 23.8.5 didr0 ? digital in put disable register 0 ? bit 7:0 ? adc7d:adc0d: ad c7:0 digital input disable when this bit is written logic one, the digita l input buffer on the corresponding adc pin is dis- abled. the corresponding pin regist er bit will always read as zero when this bit is set. when an analog signal is applied to the adc7..0 pin and the digital input from this pin is not needed, this bit should be written logic one to reduce power consumption in the digital input buffer. bit 76543210 (0x7b) ? acme ? ? ? adts2 adts1 adts0 adcsrb read/write r r/w r r r r/w r/w r/w initial value 0 0 0 0 0 0 0 0 table 23-6. adc auto trigger source selections adts2 adts1 adts0 trigger source 0 0 0 free running mode 0 0 1 analog comparator 0 1 0 external interrupt request 0 0 1 1 timer/counter0 compare matcha 1 0 0 timer/counter0 overflow 1 0 1 timer/counter1 compare match b 1 1 0 timer/counter1 overflow 1 1 1 timer/counter1 capture event bit 76543210 (0x7e) adc7d adc6d adc5d adc4d adc3d adc2d adc1d adc0d didr0 read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value00000000 218 2570n?avr?05/11 atmega325/3250/645/6450 24. jtag interface and on-chip debug system 24.1 features ? jtag (ieee std. 1149.1 compliant) interface ? boundary-scan ca pabilities according to the i eee std. 1149.1 (jtag) standard ? debugger access to: ? all internal peripheral units ? internal and external ram ? the internal register file ? program counter ? eeprom and flash memories ? extensive on-chip debug support for break conditions, including ? avr break instruction ? break on change of program memory flow ? single step break ? program memory break points on single address or address range ? data memory break points on single address or address range ? programming of flash, eeprom , fuses, and lock bits th rough the jtag interface ? on-chip debugging supported by avr studio ? 24.2 overview the avr ieee std. 1149.1 compliant jtag interface can be used for ? testing pcbs by using the jtag boundary-scan capability ? programming the non-volatile memories, fuses and lock bits ? on-chip debugging a brief description is given in the following se ctions. detailed descriptions for programming via the jtag interface, and using the boundary-scan chain can be found in the sections ?program- ming via the jtag interface? on page 2 8 4 and ?ieee 1149.1 (jtag) bo undary-scan? on page 224 , respectively. the on-chip debug support is considered being private jtag instructions, and distributed within atmel and to selected third party vendors only. figure 24-1 shows a block diagram of the jtag interface and the on-chip debug system. the tap controller is a state machine controlled by the tck and tms signals. the tap controller selects either the jtag instruction register or one of several data registers as the scan chain (shift register) between the tdi ? input and tdo ? output. the instruction register holds jtag instructions controlling the be havior of a data register. the id-register, bypass register, and the bou ndary-scan chain are the data registers used for board-level testing. the jtag programming interface (actually consisting of several physical and virtual data registers) is used for serial programming via the jtag interface. the internal scan chain and break point scan chain are used for on-chip debugging only. 24.3 tap ? test access port the jtag interface is accessed through four of the avr?s pins. in jtag terminology, these pins constitute the test access port ? tap. these pins are: ? tms: test mode select. this pin is used for navigating through the tap-controller state machine. ? tck: test clock. jtag operation is synchronous to tck. ? tdi: test data in. serial input data to be shifted in to the instruction register or data register (scan chains). 219 2570n?avr?05/11 atmega325/3250/645/6450 ? tdo: test data out. serial output data from instruction register or data register. the ieee std. 1149.1 also specifies an optional tap signal; trst ? test reset ? which is not provided. when the jtagen fuse is unprogrammed, these four tap pins are normal port pins and the tap controller is in reset. when programmed and the jtd bit in mcucsr is cleared, the tap pins are internally pulled high and the jtag is enabled for boundary-scan and programming. the device is shipped with this fuse programmed. for the on-chip debug system, in addition to the jtag interface pins, the reset pin is moni- tored by the debugger to be able to detect external reset sources. the debugger can also pull the reset pin low to reset the whole system, assuming only open collectors on the reset line are used in the application. figure 24-1. block diagram tap controller tdi tdo tck tms flash memory avr cpu digital peripheral units jtag / avr core communication interface breakpoint unit flow control unit ocd status and control internal scan chain m u x instruction register id register bypass register jtag programming interface pc instruction address data breakpoint scan chain address decoder analog peripherial units i/o port 0 i/o port n boundary scan chain analog inputs control & clock lines device boundary 220 2570n?avr?05/11 atmega325/3250/645/6450 figure 24-2. tap controller state diagram 24.4 tap controller the tap controller is a 16-state finite state machine that controls the operation of the boundary- scan circuitry, jtag programming circuitry, or on-chip debug system. the state transitions depicted in figure 24-2 depend on the signal present on tm s (shown adjacent to each state transition) at the time of the rising edge at tck. the initial state after a power-on reset is test- logic-reset. as a definition in this document, the lsb is shifted in and out first for all shift registers. assuming run-test/idle is the present state, a typical scenario for using the jtag interface is: ? at the tms input, apply the sequence 1, 1, 0, 0 at the rising edges of tck to enter the shift instruction register ? shift-ir state. while in this state, shift the four bits of the jtag instructions into the jtag instruction register from the tdi input at the rising edge of tck. the tms input must be held low during input of the 3 lsbs in order to remain in the shift-ir state. the msb of the instruction is shifted in when this state is left by setting tms high. while the instruction is shifted in from the tdi pin, the captured ir-state 0x01 is shifted out on the tdo pin. the jtag instruction selects a particular data register as path between tdi and tdo and controls the circuitry surrounding the selected data register. test-logic-reset run-test/idle shift-dr exit1-dr pause-dr exit2-dr update-dr select-ir scan capture-ir shift-ir exit1-ir pause-ir exit2-ir update-ir select-dr scan capture-dr 0 1 0 11 1 00 00 11 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 0 0 1 1 221 2570n?avr?05/11 atmega325/3250/645/6450 ? apply the tms sequence 1, 1, 0 to re-enter the run-test/idle state. the instruction is latched onto the parallel output from the shift register path in the update-ir state. the exit- ir, pause-ir, and exit2-ir states are onl y used for navigating the state machine. ? at the tms input, apply the sequence 1, 0, 0 at the rising edges of tck to enter the shift data register ? shift-dr state. while in this state, upload the selected data register (selected by the present jtag instruction in the jtag instruction register) from the tdi input at the rising edge of tck. in order to remain in the shift-dr state, the tms input must be held low during input of all bits except the msb. the msb of the data is shifted in when this state is left by setting tms high. while the data register is shifted in from the tdi pin, the parallel inputs to the data register captured in the capture-dr state is shifted out on the tdo pin. ? apply the tms sequence 1, 1, 0 to re-enter the run-test/idle state. if the selected data register has a latched parallel-output, the latching takes place in the update-dr state. the exit-dr, pause-dr, and exit2-dr states are only used for navigating the state machine. as shown in the state diagram, the run-test/idle state need not be entered between selecting jtag instruction and using data registers, and some jtag instructions may select certain functions to be performed in the run-test/idle, making it unsuitable as an idle state. note: independent of the initial state of the tap c ontroller, the test-logic-r eset state can always be entered by holding tms high for five tck clock periods. for detailed information on the jtag specification, refer to the literature listed in ?bibliography? on page 223 . 24.5 using the b oundary-scan chain a complete description of the boundary-sc an capabilities are gi ven in the section ?ieee 1149.1 (jtag) boundary-scan? on page 224 . 24.6 using the on-c hip debug system as shown in figure 24-1 , the hardware support for on-chi p debugging consists mainly of ? a scan chain on the interface between the internal avr cpu and the internal peripheral units. ? break point unit. ? communication interface between the cpu and jtag system. all read or modify/write operations needed for implementing the debugger are done by applying avr instructions via the internal avr cpu scan chain. the cpu sends the result to an i/o memory mapped location which is part of the communication interface between the cpu and the jtag system. the break point unit implements break on change of program flow, single step break, two program memory break points, and two combined break points. together, the four break points can be configured as either: ? 4 single program memory break points. ? 3 single program memory break point + 1 single data memory break point. ? 2 single program memory break points + 2 single data memory break points. ? 2 single program memory break points + 1 program memory break point with mask (?range break point?). ? 2 single program memory break points + 1 data memory break point with mask (?range break point?). 222 2570n?avr?05/11 atmega325/3250/645/6450 a debugger, like the avr studio, may however use one or more of these resources for its inter- nal purpose, leaving less flexibility to the end-user. a list of the on-chip debug specific jtag instructions is given in ?on-chip debug specific jtag instructions? on page 222 . the jtagen fuse must be programmed to enable the jtag test access port. in addition, the ocden fuse must be programmed and no lock bits must be set for the on-chip debug system to work. as a security feature, the on-chip debug system is disabled when either of the lb1 or lb2 lock bits are set. otherwise, the on-chi p debug system would have provided a back-door into a secu red device. the avr studio enables the user to fully contro l execution of programs on an avr device with on-chip debug capability, avr in- circuit emulator, or the built-i n avr instruction set simulator. avr studio ? supports source level execution of assembly programs assembled with atmel cor- poration?s avr assembler and c programs compiled with third party vendors? compilers. avr studio runs under microsoft ? windows ? 95/9 8 /2000, windows nt ? and windows xp ? . for a full description of the avr studio, please re fer to the avr studio user guide. only high- lights are presented in this document. all necessary execution commands are available in avr studio, both on source level and on disassembly level. the user can execute the program, single step through the code either by tracing into or stepping over functions, step out of functions, place the cursor on a statement and execute until the statement is reached, stop th e execution, and reset the execution target. in addition, the user can have an unlimited number of code break points (using the break instruction) and up to two data memory break points, alternatively combined as a mask (range) break point. 24.7 on-chip debug specific jtag instructions the on-chip debug support is considered being private jtag instructions, and distributed within atmel and to selected third party vendors only. instruction opcodes are listed for reference. 24.7.1 private0; 0x8 private jtag instruction for accessing on-chip debug system. 24.7.2 private1; 0x9 private jtag instruction for accessing on-chip debug system. 24.7.3 private2; 0xa private jtag instruction for accessing on-chip debug system. 24.7.4 private3; 0xb private jtag instruction for accessing on-chip debug system. 223 2570n?avr?05/11 atmega325/3250/645/6450 24.8 using the jtag pr ogramming capabilities programming of avr parts via jtag is performed via the 4-pin jtag port, tck, tms, tdi, and tdo. these are the only pins that need to be controlled/observed to perform jtag program- ming (in addition to power pins). it is not requi red to apply 12v externally. the jtagen fuse must be programmed and the jtd bit in the mcucr register must be cleared to enable the jtag test access port. the jtag programmi ng capability supports: ? flash programming and verifying. ? eeprom programming and verifying. ? fuse programming and verifying. ? lock bit programming and verifying. the lock bit security is exactly as in parallel programming mode. if the lock bits lb1 or lb2 are programmed, the ocden fuse cannot be programmed unless first doing a chip erase. this is a security feature that ensures no back-door exists for reading out the content of a secured device. the details on programming through the jtag interface and programming specific jtag instructions are given in the section ?programming via the jtag interface? on page 2 8 4 . 24.9 bibliography for more information about general boundary-scan, the following literature can be consulted: ? ieee: ieee std. 1149.1-1990. ieee standard test access port and boundary-scan architecture, ieee, 1993. colin maunder: the board designers guide to testable logic circuits, addison-wesley, 1992. 24.10 register description 24.10.1 ocdr ? on-chip debug register the ocdr register provides a co mmunication channel from the running pr ogram in the micro- controller to the debugger. the cpu can transfer a byte to the debugger by writing to this location. at the same time, an in ternal flag; i/o debug register dirty ? idrd ? is set to indicate to the debugger that the register has been written. when the cpu reads the ocdr register the 7 lsb will be from the ocdr regi ster, while the msb is the idrd bit. the debugger clears the idrd bit when it has read the information. in some avr devices, this register is shared with a standard i/o location. in this case, the ocdr register can only be accessed if the ocden fuse is programmed, and the debugger enables access to the ocdr register. in all other cases, the standard i/o location is accessed. refer to the debugger documentation for further information on how to use this register. bit 7 6543210 0x31 (0x51) msb/idrd lsb ocdr read/write r/w r/w r/w r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 224 2570n?avr?05/11 atmega325/3250/645/6450 25. ieee 1149.1 (jtag) boundary-scan 25.1 features ? jtag (ieee std. 1149.1 compliant) interface ? boundary-scan capabilities acco rding to the jtag standard ? full scan of all port functions as well as analog circuitry having off-chip connections ? supports the optional idcode instruction ? additional public avr_reset instruction to reset the avr 25.2 system overview the boundary-scan chain has the capability of drivin g and observing the logi c levels on the digi- tal i/o pins, as well as the boundary between digi tal and analog logic for analog circuitry having off-chip connections. at system level, all ics having jtag capabilities ar e connected serially by the tdi/tdo signals to form a long shift register. an external controller sets up the devices to drive values at their output pins, and observe the input values received from other devices. the controller compares the received data with the expected result. in this way, boundary-scan pro- vides a mechanism for testing interconnections and integrity of components on printed circuits boards by using the four tap signals only. the four ieee 1149.1 defined mandatory jtag in structions idcode, bypass, sample/pre- load, and extest, as well as the avr specif ic public jtag instruction avr_reset can be used for testing the print ed circuit board. initial scanning of the data register path will show the id-code of the device, since idcode is the default jtag instruction. it may be desirable to have the avr device in reset during test mode. if not reset, inputs to the device may be deter- mined by the scan operations, and the internal software may be in an undetermined state when exiting the test mode. en tering reset, the outputs of any po rt pin will instantly enter the high impedance state, making the highz instruction redundant. if needed, the bypass instruction can be issued to make the shortest possible scan chain through the device. the device can be set in the reset state either by pulling the external reset pin low, or issuing the avr_reset instruction with appropriate setting of the reset data register. the extest instruction is used for sampling external pins and loading output pins with data. the data from the output latch will be driven out on the pins as soon as the extest instruction is loaded into the jtag ir-register. therefore, the sample/preload should also be used for setting initial values to the scan ring, to avoid damaging the board when issuing the extest instruction for the first time. sample/preload c an also be used for taking a snapshot of the external pins during normal operation of the part. the jtagen fuse must be pr ogrammed and the jtd bit in the i/o register mcucr must be cleared to enable the jtag test access port. when using the jtag interface for boundary-scan, using a jtag tck clock frequency higher than the internal chip frequency is possible. the chip clock is not required to run. 25.3 data registers the data registers relevant for boundary-scan operations are: ? bypass register ? device identification register ? reset register ? boundary-scan chain 225 2570n?avr?05/11 atmega325/3250/645/6450 25.3.1 bypass register the bypass register consists of a single shift register stage. when the bypass register is selected as path between tdi and tdo, the register is reset to 0 when leaving the capture-dr controller state. the bypass register can be used to shorten the scan chain on a system when the other devices are to be tested. 25.3.2 device identification register figure 25-1 shows the structure of the de vice identification register. figure 25-1. the format of the device identification register 25.3.2.1 version version is a 4-bit number identifying the revision of the component. the jtag version number follows the revision of the device. revision a is 0x0, revision b is 0x1 and so on. 25.3.2.2 part number the part number is a 16-bit code identifying the component. the jtag part number for atmel atmega325/3250/645/6450 is listed in table 25-1 . 25.3.2.3 manufacturer id the manufacturer id is a 11-bit code identifying the manufacturer. the jtag manufacturer id for atmel is listed in table 25-2 . 25.3.3 reset register the reset register is a test data register used to reset the part. since the avr tri-states port pins when reset, the reset register can also replace the function of the unimplemented optional jtag instruction highz. a high value in the reset register corresponds to pulling the external reset low. the part is reset as long as there is a high value present in the reset register. depending on the fuse set- tings for the clock options, the part will remain reset for a reset time-out period (refer to ?clock msb lsb bit 31 28 27 12 11 1 0 device id version part number manufacturer id 1 4 bits 16 bits 11 bits 1-bit table 25-1. avr jtag part number part number jtag part number (hex) atmega325 0x9505 atmega3250 0x9506 atmega645 0x9605 atmega6450 0x9606 table 25-2. manufacturer id manufacturer jtag manufacturer id (hex) at m e l 0 x 0 1 f 226 2570n?avr?05/11 atmega325/3250/645/6450 sources? on page 27 ) after releasing the reset register. the output from this data register is not latched, so the reset will take place immediately, as shown in figure 25-2 . figure 25-2. reset register 25.3.4 boundary-scan chain the boundary-scan chain has the capability of driv ing and observing the lo gic levels on the dig- ital i/o pins, as well as the boundary between di gital and analog logic for analog circuitry having off-chip connections. see ?boundary-scan chain? on page 22 8 for a complete description. 25.4 boundary-scan specifi c jtag instructions the instruction register is 4-bit wide, suppor ting up to 16 instructions. listed below are the jtag instructions useful for boundary-scan operation. note that the optional highz instruction is not implemented, but all outputs with tri-stat e capability can be set in high-impedant state by using the avr_reset instruction, since the initial state for all port pins is tri-state. as a definition in this data sheet, the lsb is shifted in and out first for all shift registers. the opcode for each instruction is shown behind the instruction name in hex format. the text describes which data register is selected as path between tdi and tdo for each instruction. 25.4.1 extest; 0x0 mandatory jtag instruction for selecting the boundary-scan chain as data register for testing circuitry external to the avr package. for port- pins, pull-up disable, output control, output data, and input data are all accessible in the scan chain. for analog ci rcuits having off-chip connections, the interface between the analog and th e digital logic is in the scan chain. the con- tents of the latched outputs of the boundary-scan chain is driven out as soon as the jtag ir- register is loaded with the extest instruction. the active states are: ? capture-dr: data on the external pins are sampled into the boundary-scan chain. ? shift-dr: the internal scan chain is shifted by the tck input. ? update-dr: data from the scan chain is applied to output pins. dq from tdi clockdr avr_reset to tdo from other internal and external reset sources internal reset 227 2570n?avr?05/11 atmega325/3250/645/6450 25.4.2 idcode; 0x1 optional jtag instruction selecting the 32 bit id-register as data register. the id-register consists of a version number, a device number and the manufacturer code chosen by jedec. this is the default inst ruction after power-up. the active states are: ? capture-dr: data in the idcode register is sampled into the boundary-scan chain. ? shift-dr: the idcode scan chai n is shifted by the tck input. 25.4.3 sample_preload; 0x2 mandatory jtag instruction for pre-loading the output latches and taking a snap-shot of the input/output pins without affecting the system operation. however, the output latches are not connected to the pins. the boundary-scan chain is selected as data register. the active states are: ? capture-dr: data on the external pins are sampled into the boundary-scan chain. ? shift-dr: the boundary-scan chain is shifted by the tck input. ? update-dr: data from the boundary-scan chain is applied to the output latches. however, the output latches are not connected to the pins. 25.4.4 avr_reset; 0xc the avr specific public jtag instruction for forcing the avr device into the reset mode or releasing the jtag reset source. the tap controller is not reset by this in struction. the one bit reset register is selected as da ta register. note that the reset will be active as long as there is a logic ?one? in the reset chain. the output from this chain is not latched. the active states are: ? shift-dr: the reset register is shifted by the tck input. 25.4.5 bypass; 0xf mandatory jtag instructio n selecting the bypass register for data register. the active states are: ? capture-dr: loads a logic ?0? into the bypass register. ? shift-dr: the bypass register cell between tdi and tdo is shifted. 25.5 boundary-scan related re gister in i/o memory 25.5.1 mcucr ? mcu control register the mcu control register contains control bits for general mcu functions. ? bit 7 ? jtd: jtag interface disable when this bit is zero, the jtag interface is ena bled if the jtagen fuse is programmed. if this bit is one, the jtag interface is disabled. in or der to avoid unintentional disabling or enabling of the jtag interface, a timed sequence must be followed when changing this bit: the application bit 76543210 0x35 (0x55) jtd ? ? pud ? ? ivsel ivce mcucr read/write r/w r r r/w r r r/w r/w initial value 0 0 0 0 0 0 0 0 228 2570n?avr?05/11 atmega325/3250/645/6450 software must write this bit to the desired value twice within four cycles to change its value. note that this bit must not be altered when using the on-chip debug system. if the jtag interface is left unconnected to ot her jtag circuitry, the jtd bit should be set to one. the reason for this is to avoid static current at the tdo pin in the jtag interface. 25.5.2 mcusr ? mcu status register the mcu status register provides information on which reset source caused an mcu reset. ? bit 4 ? jtrf: jtag reset flag this bit is set if a reset is being caused by a logic one in the jtag reset register selected by the jtag instruction avr_reset. this bit is rese t by a power-on reset, or by writing a logic zero to the flag. 25.6 boundary-scan chain the boundary-scan chain has the capability of drivin g and observing the logi c levels on the digi- tal i/o pins, as well as the boundary between digi tal and analog logic for analog circuitry having off-chip connection. 25.6.1 scanning the digital port pins figure 25-3 shows the boundary-scan cell for a bi-directional port pin with pull-up function. the cell consists of a standard boundary-scan cell for the pull-up enable ? puexn ? function, and a bi-directional pin cell that combines the three signals output control ? ocxn, output data ? odxn, and input data ? idxn, into only a two-stage shift register. the port and pin indexes are not used in the following description the boundary-scan logic is not included in the figures in the data sheet. figure 25-4 shows a simple digital port pin as described in the section ?i/o-ports? on page 60 . the boundary-scan details from figure 25-3 replaces the dashed box in figure 25-4 . when no alternate port function is present, t he input data ? id ? corresponds to the pinxn reg- ister value (but id has no synchronizer), output data corresponds to the port register, output control corresponds to the data direction ? dd register, and the pull-up enable ? puexn ? cor- responds to logic expression pud ddxn portxn. digital alternate port functions are connected outside the dotted box in figure 25-4 to make the scan chain read the actual pin value. for analog function, there is a direct connection from the external pin to the analog circuit, and a scan ch ain is inserted on the interface between the digi- tal logic and the analog circuitry. bit 76543210 0x34 (0x54) ? ? ?jtrf wdrf borf extrf porf mcusr read/write r r r r/w r/w r/w r/w r/w initial value 0 0 0 see bit description 229 2570n?avr?05/11 atmega325/3250/645/6450 figure 25-3. boundary-scan cell for bi-directional port pin with pull-up function. dq dq g 0 1 0 1 dq dq g 0 1 0 1 0 1 0 1 dq dq g 0 1 port pin (pxn) vcc extest to next cell shiftdr output control (oc) pullup enable (pue) output data (od) input data (id) from last cell updatedr clockdr ff2 ld2 ff1 ld1 ld0 ff0 230 2570n?avr?05/11 atmega325/3250/645/6450 figure 25-4. general port pin schematic diagram 25.6.2 scanning the reset pin the reset pin accepts 5v active low logic fo r standard reset operation, and 12v active high logic for high voltage parallel programming. an observe-only cell as shown in figure 25-5 is inserted both for the 5v reset signal; rstt, and the 12v reset signal; rsthv. figure 25-5. observe-only cell clk rpx rdx wdx pud synchronizer wdx: write ddrx wrx: write portx rrx: read portx register wpx: write pinx register pud: pullup disable clk : i/o clock rdx: read ddrx d l q q reset q q d q q d clr ddxn pinxn data b u s sleep sleep: sleep control pxn i/o i/o see boundary-scan description for details! puexn ocxn odxn idxn puexn: pullup enable for pin pxn ocxn: output control for pin pxn odxn: output data to pin pxn idxn: input data from pin pxn rpx: read portx pin rrx reset q q d clr portxn wpx 0 1 wrx 0 1 dq from previous cell clockdr shiftdr to next cell from system pin to system logic ff1 231 2570n?avr?05/11 atmega325/3250/645/6450 25.6.3 scanning the clock pins the avr devices have many clock options selectable by fuses. these are: internal rc oscilla- tor, external clock, (high frequency) crystal oscillator, low-frequenc y crystal oscillator, and ceramic resonator. figure 25-6 shows how each oscillator with external co nnection is supported in the scan chain. the enable signal is supported with a general bo undary-scan cell, while the oscillator/clock out- put is attached to an obs erve-only cell. in additi on to the main clock, the timer oscillator is scanned in the same way. the output from the internal rc oscillator is not scanned, as this oscillator does not have external connections. figure 25-6. boundary-scan cells for os cillators and clock options table 25-3 summaries the scan registers for the exte rnal clock pin xtal1, oscillators with xtal1/xtal2 connections as we ll as 32khz timer oscillator. note: 1. do not enable more than one clock source as main clock at a time. 2. scanning an oscillator output gives unpredictable results as there is a frequency drift between the internal oscillator and the jtag tck clock. if possible, scanning an external clock is preferred. 3. the clock configuration is programmed by fuses. as a fuse is not changed run-time, the clock configuration is considered fixed for a given app lication. the user is advised to scan the same clock option as to be used in the final system. the enable signals are supported in the scan chain because the system logic c an disable clock options in sl eep modes, thereby disconnect- ing the oscillator pins from the scan path if not provided. table 25-3. scan signals for the oscillator (1)(2)(3) enable signal scanned clock line clock option scanned clock line when not used extclken extclk (xtal1) external clock 0 oscon oscck external crystal external ceramic resonator 1 osc32en osc32ck low freq. external crystal 1 0 1 dq from previous cell clockdr shiftdr to next cell to system logic ff1 0 1 dq dq g 0 1 from previous cell clockdr updatedr shiftdr to next cell extest from digital logic xtal1/tosc1 xtal2/tosc2 oscillator enable output 232 2570n?avr?05/11 atmega325/3250/645/6450 25.6.4 scanning the analog comparator the relevant comparator signals regarding boundary-scan are shown in figure 25-7 . the boundary-scan cell from figure 25- 8 is attached to each of these signals. the signals are described in table 25-4 . the comparator need not be used for pure connectivity testing, since all analog inputs are shared with a digital port pin as well. figure 25-7. analog comparator figure 25-8. general boundary-scan cell used for signals for comparator and adc acbg bandgap reference adc multiplexer output acme ac_idle aco adcen acd 0 1 dq dq g 0 1 from previous cell clockdr updatedr shiftdr to next cell extest to analog circuitry/ to digital logic from digital logic/ from analog ciruitry 233 2570n?avr?05/11 atmega325/3250/645/6450 25.6.5 scanning the adc figure 25-9 shows a block diagram of the adc with all relevant control and observe signals. the boundary-scan cell from figure 25-5 is attached to each of these signals. the adc need not be used for pure connectivity testing, since all analog inputs are shared with a digital port pin as well. figure 25-9. analog to digital converter the signals are described briefly in table 25-5 . table 25-4. boundary-scan signals for the analog comparator signal name direction as seen from the comparator description recommended input when not in use output values when recommended inputs are used ac_idle input turns off analog comparator when true 1 depends upon c code being executed aco output analog comparator output will become input to c code being executed 0 acme input uses output signal from adc mux when true 0 depends upon c code being executed acbg input bandgap reference enable 0 depends upon c code being executed 10-bit dac + - aref prech dacout comp muxen_7 adc_7 muxen_6 adc_6 muxen_5 adc_5 muxen_4 adc_4 muxen_3 adc_3 muxen_2 adc_2 muxen_1 adc_1 muxen_0 adc_0 negsel_2 adc_2 negsel_1 adc_1 negsel_0 adc_0 extch + - 1x st aclk ampen 1.11v ref irefen aref vccren dac_ 9 ..0 adcen hold prech gnden passen comp sctest adcbgen to comparator 1.22v ref acten aref 234 2570n?avr?05/11 atmega325/3250/645/6450 table 25-5. boundary-scan signals for the adc (1) signal name direction as seen from the adc description recommended input when not in use output values when recommended inputs are used, and cpu is not using the adc comp output comparator output 0 0 aclk input clock signal to differential amplifier implemented as s witch-cap filters 00 acten input enable path from differential amplifier to the comparator 00 adcbgen input enable band-gap reference as negative input to comparator 00 adcen input power-on signal to the adc 0 0 ampen input power-on signal to the differential amplifier 0 0 dac_9 input bit 9 of digital value to dac 1 1 dac_ 8 input bit 8 of digital value to dac 0 0 dac_7 input bit 7 of digital value to dac 0 0 dac_6 input bit 6 of digital value to dac 0 0 dac_5 input bit 5 of digital value to dac 0 0 dac_4 input bit 4 of digital value to dac 0 0 dac_3 input bit 3 of digital value to dac 0 0 dac_2 input bit 2 of digital value to dac 0 0 dac_1 input bit 1 of digital value to dac 0 0 dac_0 input bit 0 of digital value to dac 0 0 extch input connect adc channels 0 - 3 to by-pass path around differential amplifier 11 gnden input ground the negativ e input to comparator when true 00 hold input sample & hold signal. sample analog signal when low. hold signal when high. if differential amplifier are used, this signal must go active when aclk is high. 11 irefen input enables band-gap reference as aref signal to dac 00 muxen_7 input input mux bit 7 0 0 muxen_6 input input mux bit 6 0 0 muxen_5 input input mux bit 5 0 0 muxen_4 input input mux bit 4 0 0 muxen_3 input input mux bit 3 0 0 muxen_2 input input mux bit 2 0 0 muxen_1 input input mux bit 1 0 0 muxen_0 input input mux bit 0 1 1 235 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. incorrect setting of the switches in figure 25-9 will make signal contention and may damage the part. there are several input choices to the s&h circuitry on the negative input of the output comparator in figure 25-9 . make sure only one path is selected from either one adc pin, bandgap reference source, or ground. if the adc is not to be used during scan, the recommended input values from table 25-5 should be used. the user is recommended not to use the differential amplifier during scan. switch-cap based differential amplifier require fast operation and accurate timing which is difficult to obtain when used in a scan chain. details concerning operations of the differential amplifier is therefore not provided. the avr adc is based on the analog circuitry shown in figure 25-9 with a successive approxi- mation algorithm implemented in the digital logic. when used in boundary-scan, the problem is usually to ensure that an applied analog voltag e is measured within some limits. this can easily be done without running a successive approximation algorithm: apply the lower limit on the digi- tal dac[9:0] lines, make sure the output from the comparator is low, then apply the upper limit on the digital dac[9:0] lines, and verify the output from the comparator to be high. the adc need not be used for pure connectivity te sting, since all analog inputs are shared with a digital port pin as well. when using the adc, remember the following ? the port pin for the adc channel in use must be configured to be an input with pull-up disabled to avoid signal contention. ? in normal mode, a dummy conversion (consisting of 10 comparisons) is performed when enabling the adc. the user is advised to wait at least 200ns after enabling the adc before controlling/observing any adc si gnal, or perform a dummy conversion before using the first result. ? the dac values must be stable at the midpoi nt value 0x200 when having the hold signal low (sample mode). negsel_2 input input mux for negative input for differential signal, bit 2 00 negsel_1 input input mux for negative input for differential signal, bit 1 00 negsel_0 input input mux for negative input for differential signal, bit 0 00 passen input enable pass-gate of differential amplifier. 1 1 prech input precharge output latch of comparator. (active low) 11 sctest input switch-cap test enable. output from differential amplifier send out to port pin having adc_4 00 st input output of differential amplifier will settle faster if this signal is high first two aclk periods after ampen goes high. 00 vccren input selects vcc as the acc reference voltage. 0 0 table 25-5. boundary-scan signals for the adc (1) (continued) signal name direction as seen from the adc description recommended input when not in use output values when recommended inputs are used, and cpu is not using the adc 236 2570n?avr?05/11 atmega325/3250/645/6450 as an example, consider the task of verifying a 1.5v 5% input signal at adc channel 3 when the power supply is 5.0v and aref is externally connected to v cc . the recommended values from table 25-5 are used unless other values are given in the algo- rithm in table 25-6 . only the dac and port pin values of the scan chain are shown. the column ?actions? describes what jtag instruction to be used before filling the boundary-scan register with the succeeding columns. the verification should be done on the data scanned out when scanning in the data on the same row in the table. using this algorithm, the timing constraint on the hold signal constrains the tck clock fre- quency. as the algorithm keeps hold high for fi ve steps, the tck clock frequency has to be at least five times the number of scan bits divided by the maximum hold time, t hold,max table 25-6. algorithm for using the adc step actions adcen dac muxen hold prech pa 3 . data pa3. control pa3. pull- up_ enable 1 sample_ preload 1 0x200 0x0 8 1100 0 2 extest 1 0x200 0x0 8 0100 0 3 1 0x200 0x0 8 1100 0 4 1 0x123 0x0 8 1100 0 5 1 0x123 0x0 8 1000 0 6 verify the comp bit scanned out to be 0 1 0x200 0x0 8 1100 0 7 1 0x200 0x0 8 0100 0 8 1 0x200 0x0 8 1100 0 9 1 0x143 0x0 8 1100 0 10 1 0x143 0x0 8 1000 0 11 verify the comp bit scanned out to be 1 1 0x200 0x0 8 1100 0 the lower limit is: 1024 1.5 v 0,95 5 v ? ?? 291 0x123 == the upper limit is: 1024 1.5 v 1.05 5 v ? ?? 323 0x143 == 237 2570n?avr?05/11 atmega325/3250/645/6450 25.7 boundary-scan order table 25-7 and table 25- 8 shows the scan order between tdi and tdo when the boundary- scan chain is selected as data path. bit 0 is the lsb; the first bit scanned in, and the first bit scanned out. the scan order follows the pin-out order as far as possible. therefore, the bits of port a is scanned in the opposite bit order of the other ports. exceptions from the rules are the scan chains for the analog circuits, which constitute the most significant bits of the scan chain regardless of which physical pin they are connected to. in figure 25-3 , pxn. data corresponds to ff0, pxn. control corresponds to ff1, and px n. pull-up_enable corresponds to ff2. bit 4, 5, 6 and 7 of port f is not in the scan chain, sinc e these pins constitute the tap pins when the jtag is enabled. table 25-7. atmega325/645 boundary-scan order, 64-pin bit number signal name module 197 ac_idle comparator 196 aco 195 acme 194 ainbg 238 2570n?avr?05/11 atmega325/3250/645/6450 193 comp adc 192 aclk 191 acten 190 private_signal1 (1) 1 8 9 adcbgen 1 88 adcen 1 8 7 ampen 1 8 6dac_9 1 8 5dac_ 8 1 8 4dac_7 1 8 3dac_6 1 8 2dac_5 1 8 1dac_4 1 8 0dac_3 179 dac_2 17 8 dac_1 177 dac_0 176 extch 175 gnden 174 hold 173 irefen 172 muxen_7 171 muxen_6 170 muxen_5 169 muxen_4 16 8 muxen_3 167 muxen_2 166 muxen_1 165 muxen_0 164 negsel_2 163 negsel_1 162 negsel_0 161 passen 160 prech 159 st 15 8 vccren table 25-7. atmega325/645 boundary-scan order, 64-pin (continued) bit number signal name module 239 2570n?avr?05/11 atmega325/3250/645/6450 157 pe0.data port e 156 pe0.control 155 pe0.pull-up_enable 154 pe1.data 153 pe1.control 152 pe1.pull-up_enable 151 pe2.data 150 pe2.control 149 pe2.pull-up_enable 14 8 pe3.data 147 pe3.control 146 pe3.pull-up_enable 145 pe4.data 144 pe4.control 143 pe4.pull-up_enable 142 pe5.data 141 pe5.control 140 pe5.pull-up_enable 139 pe6.data 13 8 pe6.control 137 pe6.pull-up_enable 136 pe7.data 135 pe7.control 134 pe7.pull-up_enable table 25-7. atmega325/645 boundary-scan order, 64-pin (continued) bit number signal name module 240 2570n?avr?05/11 atmega325/3250/645/6450 133 pb0.data port b 132 pb0.control 131 pb0.pull-up_enable 130 pb1.data 129 pb1.control 12 8 pb1.pull-up_enable 127 pb2.data 126 pb2.control 125 pb2.pull-up_enable 124 pb3.data 123 pb3.control 122 pb3.pull-up_enable 121 pb4.data 120 pb4.control 119 pb4.pull-up_enable 11 8 pb5.data 117 pb5.control 116 pb5.pull-up_enable 115 pb6.data 114 pb6.control 113 pb6.pull-up_enable 112 pb7.data 111 pb7.control 110 pb7.pull-up_enable 109 pg3.data port g 10 8 pg3.control 107 pg3.pull-up_enable 106 pg4.data 105 pg4.control 104 pg4.pull-up_enable 103 pg5 (observe only) 102 rstt reset logic (observe-only) 101 rsthv table 25-7. atmega325/645 boundary-scan order, 64-pin (continued) bit number signal name module 241 2570n?avr?05/11 atmega325/3250/645/6450 100 extclken enable signals for main clock/oscillators 99 oscon 9 8 rcoscen 97 osc32en 96 extclk (xtal1) clock input and oscillators for the main clock (observe-only) 95 oscck 94 rcck 93 osc32ck 92 pd0.data port d 91 pd0.control 90 pd0.pull-up_enable 8 9pd1.data 88 pd1.control 8 7 pd1.pull-up_enable 8 6pd2.data 8 5 pd2.control 8 4 pd2.pull-up_enable 8 3pd3.data 8 2 pd3.control 8 1 pd3.pull-up_enable 8 0pd4.data 79 pd4.control 7 8 pd4.pull-up_enable 77 pd5.data 76 pd5.control 75 pd5.pull-up_enable 74 pd6.data 73 pd6.control 72 pd6.pull-up_enable 71 pd7.data 70 pd7.control 69 pd7.pull-up_enable 6 8 pg0.data port g 67 pg0.control 66 pg0.pull-up_enable 65 pg1.data table 25-7. atmega325/645 boundary-scan order, 64-pin (continued) bit number signal name module 242 2570n?avr?05/11 atmega325/3250/645/6450 64 pg1.control 63 pg1.pull-up_enable 62 pc0.data port c 61 pc0.control 60 pc0.pull-up_enable 59 pc1.data 5 8 pc1.control 57 pc1.pull-up_enable 56 pc2.data 55 pc2.control 54 pc2.pull-up_enable 53 pc3.data 52 pc3.control 51 pc3.pull-up_enable 50 pc4.data 49 pc4.control 4 8 pc4.pull-up_enable 47 pc5.data 46 pc5.control 45 pc5.pull-up_enable 44 pc6.data 43 pc6.control 42 pc6.pull-up_enable 41 pc7.data 40 pc7.control 39 pc7.pull-up_enable 3 8 pg2.data port g 37 pg2.control 36 pg2.pull-up_enable 35 pa7.data port a 34 pa7.control 33 pa7.pull-up_enable 32 pa6.data 31 pa6.control 30 pa6.pull-up_enable 29 pa5.data table 25-7. atmega325/645 boundary-scan order, 64-pin (continued) bit number signal name module 243 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. private_signal1 should always be scanned in as zero. 2 8 pa5.control 27 pa5.pull-up_enable 26 pa4.data 25 pa4.control 24 pa4.pull-up_enable 23 pa3.data 22 pa3.control 21 pa3.pull-up_enable 20 pa2.data 19 pa2.control 1 8 pa2.pull-up_enable 17 pa1.data 16 pa1.control 15 pa1.pull-up_enable 14 pa0.data 13 pa0.control 12 pa0.pull-up_enable 11 pf3.data port f 10 pf3.control 9 pf3.pull-up_enable 8 pf2.data 7 pf2.control 6 pf2.pull-up_enable 5pf1.data 4 pf1.control 3 pf1.pull-up_enable 2pf0.data 1 pf0.control 0 pf0.pull-up_enable table 25-7. atmega325/645 boundary-scan order, 64-pin (continued) bit number signal name module 244 2570n?avr?05/11 atmega325/3250/645/6450 table 25-8. atmega3250/6450 boundary-scan order, 100-pin bit number signal name module 242 ac_idle comparator 241 aco 240 acme 239 ainbg 23 8 comp adc 237 aclk 236 acten 235 private_signal1 (1) 234 adcbgen 233 adcen 232 ampen 231 dac_9 230 dac_ 8 229 dac_7 22 8 dac_6 227 dac_5 226 dac_4 225 dac_3 224 dac_2 223 dac_1 222 dac_0 221 extch 220 gnden 219 hold 21 8 irefen 217 muxen_7 216 muxen_6 215 muxen_5 214 muxen_4 213 muxen_3 212 muxen_2 211 muxen_1 210 muxen_0 209 negsel_2 20 8 negsel_1 245 2570n?avr?05/11 atmega325/3250/645/6450 207 negsel_0 206 passen 205 prech 204 st 203 vccren 202 pe0.data port e 201 pe0.control 200 pe0.pull-up_enable 199 pe1.data 19 8 pe1.control 197 pe1.pull-up_enable 196 pe2.data 195 pe2.control 194 pe2.pull-up_enable 193 pe3.data 192 pe3.control 191 pe3.pull-up_enable 190 pe4.data 1 8 9 pe4.control 1 88 pe4.pull-up_enable 1 8 7 pe5.data 1 8 6 pe5.control 1 8 5 pe5.pull-up_enable 1 8 4 pe6.data 1 8 3 pe6.control 1 8 2 pe6.pull-up_enable 1 8 1 pe7.data 1 8 0 pe7.control 179 pe7.pull-up_enable 17 8 pj0.data port j 177 pj0.control 176 pj0.pull-up_enable 175 pj1.data 174 pj1.control 173 pj1.pull-up_enable 172 pb0.data port b table 25-8. atmega3250/6450 boundary-scan order, 100-pin (continued) bit number signal name module 246 2570n?avr?05/11 atmega325/3250/645/6450 171 pb0.control 170 pb0.pull-up_enable 169 pb1.data 16 8 pb1.control 167 pb1.pull-up_enable 166 pb2.data 165 pb2.control 164 pb2.pull-up_enable 163 pb3.data 162 pb3.control 161 pb3.pull-up_enable 160 pb4.data 159 pb4.control 15 8 pb4.pull-up_enable 157 pb5.data 156 pb5.control 155 pb5.pull-up_enable 154 pb6.data 153 pb6.control 152 pb6.pull-up_enable 151 pb7.data 150 pb7.control 149 pb7.pull-up_enable 14 8 pg3.data port g 147 pg3.control 146 pg3.pull-up_enable 145 pg4.data 144 pg4.control 143 pg4.pull-up_enable 142 pg5 (observe only) 141 rstt reset logic (observe-only) 140 rsthv 139 extclken enable signals for main clock/oscillators 13 8 oscon 137 rcoscen 136 osc32en table 25-8. atmega3250/6450 boundary-scan order, 100-pin (continued) bit number signal name module 247 2570n?avr?05/11 atmega325/3250/645/6450 135 extclk (xtal1) clock input and oscillators for the main clock (observe-only) 134 oscck 133 rcck 132 osc32ck 131 pj2.data port j 130 pj2.control 129 pj2.pull-up_enable 12 8 pj3.data 127 pj3.control 126 pj3.pull-up_enable 125 pj4.data 124 pj4.control 123 pj4.pull-up_enable 122 pj5.data 121 pj5.control 120 pj5.pull-up_enable 119 pj6.data 11 8 pj6.control 117 pj6.pull-up_enable 116 pd0.data port d 115 pd0.control 114 pd0.pull-up_enable 113 pd1.data 112 pd1.control 111 pd1.pull-up_enable 110 pd2.data 109 pd2.control 10 8 pd2.pull-up_enable 107 pd3.data 106 pd3.control 105 pd3.pull-up_enable 104 pd4.data 103 pd4.control 102 pd4.pull-up_enable 101 pd5.data 100 pd5.control table 25-8. atmega3250/6450 boundary-scan order, 100-pin (continued) bit number signal name module 248 2570n?avr?05/11 atmega325/3250/645/6450 99 pd5.pull-up_enable 9 8 pd6.data 97 pd6.control 96 pd6.pull-up_enable 95 pd7.data 94 pd7.control 93 pd7.pull-up_enable 92 pg0.data port g 91 pg0.control 90 pg0.pull-up_enable 8 9pg1.data 88 pg1.control 8 7 pg1.pull-up_enable 8 6 pc0.data port c 8 5 pc0.control 8 4 pc0.pull-up_enable 8 3pc1.data 8 2 pc1.control 8 1 pc1.pull-up_enable 8 0pc2.data 79 pc2.control 7 8 pc2.pull-up_enable 77 pc3.data 76 pc3.control 75 pc3.pull-up_enable 74 pc4.data 73 pc4.control 72 pc4.pull-up_enable 71 pc5.data 70 pc5.control 69 pc5.pull-up_enable 6 8 ph0.data port h 67 ph0.control 66 ph0.pull-up_enable 65 ph1.data 64 ph1.control table 25-8. atmega3250/6450 boundary-scan order, 100-pin (continued) bit number signal name module 249 2570n?avr?05/11 atmega325/3250/645/6450 63 ph1.pull-up_enable 62 ph2.data 61 ph2.control 60 ph2.pull-up_enable 59 ph3.data 5 8 ph3.control 57 ph3.pull-up_enable 56 pc6.data port c 55 pc6.control 54 pc6.pull-up_enable 53 pc7.data 52 pc7.control 51 pc7.pull-up_enable 50 pg2.data port g 49 pg2.control 4 8 pg2.pull-up_enable 47 pa7.data port a 46 pa7.control 45 pa7.pull-up_enable 44 pa6.data 43 pa6.control 42 pa6.pull-up_enable 41 pa5.data 40 pa5.control 39 pa5.pull-up_enable 3 8 pa 4 . d a t a 37 pa4.control 36 pa4.pull-up_enable 35 pa3.data 34 pa3.control 33 pa3.pull-up_enable 32 pa2.data 31 pa2.control 30 pa2.pull-up_enable 29 pa1.data 2 8 pa1.control table 25-8. atmega3250/6450 boundary-scan order, 100-pin (continued) bit number signal name module 250 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. private_signal1 should always be scanned in as zero. 25.8 boundary-scan description language files boundary-scan description language (bsdl) files describe boundary-scan capable devices in a standard format used by automated test-generation software. the order and function of bits in the boundary-scan data register are included in this description. a bsdl file for atmel atmega325/3250/645/6450 is available. 27 pa1.pull-up_enable 26 pa0.data 25 pa0.control 24 pa0.pull-up_enable 23 ph4.data port h 22 ph4.control 21 ph4.pull-up_enable 20 ph5.data 19 ph5.control 1 8 ph5.pull-up_enable 17 ph6.data 16 ph6.control 15 ph6.pull-up_enable 14 ph7.data 13 ph7.control 12 ph7.pull-up_enable 11 pf3.data port f 10 pf3.control 9 pf3.pull-up_enable 8 pf2.data 7 pf2.control 6 pf2.pull-up_enable 5pf1.data 4 pf1.control 3 pf1.pull-up_enable 2pf0.data 1 pf0.control 0 pf0.pull-up_enable table 25-8. atmega3250/6450 boundary-scan order, 100-pin (continued) bit number signal name module 251 2570n?avr?05/11 atmega325/3250/645/6450 26. boot loader support ? read -while-write self-programming 26.1 features ? read-while-write self-programming ? flexible boot memory size ? high security (separate boot lock bits for a flexible protection) ? separate fuse to select reset vector ? optimized page (1) size ? code efficient algorithm ? efficient read-modify-write support note: 1. a page is a section in the flash consisting of several bytes (see table 27-10 on page 270 ) used during programming. the page organiz ation does not affect normal operation. 26.2 overview the boot loader support provides a real read- while-write self-programming mechanism for downloading and uploading program code by the m cu itself. this feature a llows flexible applica- tion software updates controlled by the mcu using a flash-resident boot loader program. the boot loader program can use any available data interface and associated protocol to read code and write (program) that code into the flash memory, or read the code from the program mem- ory. the program code within the boot loader section has the capability to write into the entire flash, including the boot loader memory. the b oot loader can thus even modify itself, and it can also erase itself from the code if the feature is not needed anymore. the size of the boot loader memory is configurable with fuses and t he boot loader has two separate sets of boot lock bits which can be set indepen dently. this gives the user a uniq ue flexibility to select differ- ent levels of protection. 26.3 application and boot loader flash sections the flash memory is organized in two main sections, the application section and the boot loader section (see figure 26-2 ). the size of the different sections is configured by the bootsz fuses as shown in table 26-6 on page 262 and figure 26-2 . these two sections can have different level of protection since they have different sets of lock bits. 26.3.1 application section the application section is the section of the flash that is used for storing the application code. the protection level for the application section can be selected by the application boot lock bits (boot lock bits 0), see table 26-2 on page 255 . the application section can never store any boot loader code since the spm instruction is disabled when executed from the application section. 26.3.2 bls ? boot loader section while the application section is used for storing the application code, the the boot loader soft- ware must be located in the bls since the spm instruction can initiate a programming when executing from the bls only. the spm instruct ion can access the entire flash, including the bls itself. the protection level for the boot loader section can be selected by the boot loader lock bits (boot lock bits 1), see table 26-3 on page 255 . 252 2570n?avr?05/11 atmega325/3250/645/6450 26.4 read-while-write and no r ead-while-write flash sections whether the cpu supports read-while-write or if the cpu is halted during a boot loader soft- ware update is dependent on which address that is being programmed. in addition to the two sections that are configurable by the bootsz fuses as described above, the flash is also divided into two fixed sections, the read-whi le-write (rww) section and the no read-while- write (nrww) section. the limit between the rww- and nrww sections is given in table 26- 7 on page 262 and figure 26-2 on page 254 . the main difference between the two sections is: ? when erasing or writing a page located inside the rww section, the nrww section can be read during the operation. ? when erasing or writing a page located inside the nrww section, the cpu is halted during the entire operation. note that the user software can never read any code that is located inside the rww section dur- ing a boot loader software operation. the syntax ?read-while-write section? refers to which section that is being programmed (erased or written), not which section that actually is being read during a boot loader software update. 26.4.1 rww ? read-while-write section if a boot loader software update is programming a page inside the rww section, it is possible to read code from the flash, but only code that is located in the nrww section. during an on- going programming, the software must ensure that the rww section never is being read. if the user software is trying to read code that is located inside the rww section (i.e., by a call/jmp/lpm or an interrupt) during programming, the software might end up in an unknown state. to avoid this, the interrupts should either be disabled or moved to the boot loader sec- tion. the boot loader section is always located in the nrww section. the rww section busy bit (rwwsb) in the store program memory cont rol and status register (spmcsr) will be read as logical one as long as the rww section is blocked for reading. after a programming is com- pleted, the rwwsb must be cleared by software before reading code located in the rww section. see ?store program memory control and status register ? spmcsr? on page 263. for details on how to clear rwwsb. 26.4.2 nrww ? no read-while-write section the code located in the nrww section can be read when the boot loader software is updating a page in the rww section. when the boot loader code updates the nrww section, the cpu is halted during the entire page erase or page write operation. table 26-1. read-while-write features which section does the z- pointer address during the programming? which section can be read during programming? is the cpu halted? read-while-write supported? rww section nrww section no yes nrww section none yes no 253 2570n?avr?05/11 atmega325/3250/645/6450 figure 26-1. read-while-write vs. no read-while-write read-while-write (rww) section no read-while-write (nrww) section z-pointer addresses rww section z-pointer addresses nrww section cpu is halted during the operation code located in nrww section can be read during the operation 254 2570n?avr?05/11 atmega325/3250/645/6450 figure 26-2. memory sections note: 1. the parameters in the figure above are given in table 26-6 on page 262 . 26.5 boot loader lock bits if no boot loader capability is n eeded, the entire flash is available for application code. the boot loader has two separate sets of boot lock bits which can be set independently. this gives the user a unique flexibility to sele ct different levels of protection. the user can select: ? to protect the entire flash from a software update by the mcu. ? to protect only the boot loader flash section from a software update by the mcu. ? to protect only the application flash section from a software update by the mcu. ? allow software update in the entire flash. see table 26-2 and table 26-3 for further details. the boot lock bits and general lock bits can be set in software and in serial or parallel programming mode, but they can be cleared by a chip erase command only. the general write lock (lock bit mode 2) does not control the pro- gramming of the flash memory by spm instruction. similarly, the general read/write lock (lock bit mode 1) does not control reading nor writing by lpm/spm, if it is attempted. 0x0000 flashend program memory bootsz = '11' application flash section boot loader flash section flashend program memory bootsz = '10' 0x0000 program memory bootsz = '01' program memory bootsz = '00' application flash section boot loader flash section 0x0000 flashend application flash section flashend end rww start nrww application flash section boot loader flash section boot loader flash section end rww start nrww end rww start nrww 0x0000 end rww, end application start nrww, start boot loader application flash section application flash section application flash section read-while-write section no read-while-write section read-while-write section no read-while-write section read-while-write section no read-while-write section read-while-write section no read-while-write section end application start boot loader end application start boot loader end application start boot loader 255 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. ?1? means unprogrammed, ?0? means programmed note: 1. ?1? means unprogrammed, ?0? means programmed 26.6 entering the b oot loader program entering the boot loader takes place by a jump or call from the application program. this may be initiated by a trigger such as a command received via usart, or spi interface. alternatively, the boot reset fuse can be programmed so that the reset vector is pointing to the boot flash start address after a reset. in this case, the boot loader is started after a reset. after the applica- tion code is loaded, the program can start execut ing the application code. note that the fuses cannot be changed by the mcu itself. this means that once the boot reset fuse is pro- grammed, the reset vector will always point to the boot loader reset and the fuse can only be changed through the serial or parallel programming interface. table 26-2. boot lock bit0 protection modes (application section) (1) blb0 mode blb02 blb01 protection 1 1 1 no restrictions for spm or lpm accessing the application section. 2 1 0 spm is not allowed to write to the application section. 3 0 0 spm is not allowed to write to the application section, and lpm executing from the boot loader section is not allowed to read from the application section. if interrupt vectors are placed in the boot loader section, interrupts are disabled while executing from the application section. 4 0 1 lpm executing from the b oot loader section is not allowed to read from the application section. if interrupt vectors are placed in the boot loader section, interrupts are disabled while executing from the application section. table 26-3. boot lock bit1 protection modes (boot loader section) (1) blb1 mode blb12 blb11 protection 1 1 1 no restrictions for spm or lpm accessing the boot loader section. 2 1 0 spm is not allowed to write to the boot loader section. 3 0 0 spm is not allowed to write to the boot loader section, and lpm executing from the application section is not allowed to read from the boot loader section. if interrupt vectors are placed in the application section, interrupts are disabled while executing from the boot loader section. 4 0 1 lpm executing from the application section is not allowed to read from the boot loader se ction. if interrupt vectors are placed in the application section, interrupts are disabled while executing from the boot loader section. table 26-4. boot reset fuse (1) bootrst reset address 1 reset vector = application reset (address 0x0000) 0 reset vector = boot loader reset (see table 26-6 on page 262 ) 256 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. ?1? means unprogrammed, ?0? means programmed 26.7 addressing the flash during self-programming the z-pointer is used to address the spm commands. since the flash is organized in pages (see table 27-10 on page 270 ), the program counter can be treated as having two different sections. one sect ion, consisting of the least significant bits, is addressing the words within a page, while the most significant bits are addressing the pages. this is shown in figure 26-3 . note that the page erase and page write operations are addressed independently. therefore it is of major importance that the boot loader software addresses the same page in both the page erase and page write operation. once a program- ming operation is initiated, the address is latched and the z-pointer can be used for other operations. the only spm operation that does not use the z-pointer is setting the boot loader lock bits. the content of the z-pointer is ignored and will have no effect on the operation. the lpm instruction does also use the z-pointer to store the address. since this instruction addresses the flash byte-by-byte, also the lsb (bit z0) of the z-pointer is used. figure 26-3. addressing the flash during spm (1) note: 1. the different variables used in figure 26-3 are listed in table 26- 8 on page 262 . 2. pcpage and pcword are listed in table 27-10 on page 270 . bit 151413121110 9 8 zh (r31) z15 z14 z13 z12 z11 z10 z9 z8 zl (r30) z7z6z5z4z3z2z1z0 76543210 program memory 0 1 15 z - register bit 0 zpagemsb word address within a page page address within the flash zpcmsb instruction word pag e pcword[pagemsb:0]: 00 01 02 pageend pag e pcword pcpage pcmsb pagemsb program counter 257 2570n?avr?05/11 atmega325/3250/645/6450 26.8 self-programming the flash the program memory is updated in a page by page fashion. before programming a page with the data stored in the temporary page buffer, the page must be erased. the temporary page buf- fer is filled one word at a time using spm and the buffer can be filled either before the page erase command or between a page erase and a page write operation: alternative 1, fill the bu ffer before a page erase ? fill temporary page buffer ? perform a page erase ? perform a page write alternative 2, fill the bu ffer after page erase ? perform a page erase ? fill temporary page buffer ? perform a page write if only a part of the page needs to be changed, the rest of the page must be stored (for example in the temporary page buffer) before the erase, and then be rewritten. when using alternative 1, the boot loader provides an effective read-modify-write feature which allows the user software to first read the page, do the necessary changes, and then write back the modified data. if alter- native 2 is used, it is not possible to read the old data while loading since the page is already erased. the temporary page buffer can be accessed in a random sequence. it is essential that the page address used in both the page erase and page write operation is addressing the same page. see ?simple assembly code example for a boot loader? on page 260 for an assembly code example. 26.8.1 performing page erase by spm to execute page erase, set up the address in the z-pointer, write ?x0000011? to spmcsr and execute spm within four clock cycles after writing spmcsr. the data in r1 and r0 is ignored. the page address must be written to pcpage in the z-register. other bits in the z-pointer will be ignored during this operation. ? page erase to the rww section: the nrww section can be read during the page erase. ? page erase to the nrww section: the cpu is halted during the operation. 26.8.2 filling the temporary buffer (page loading) to write an instruction word, set up the address in the z-pointer and data in r1:r0, write ?00000001? to spmcsr and execute spm within four clock cycles after writing spmcsr. the content of pcword in the z-register is used to address the data in the temporary buffer. the temporary buffer will auto-erase after a page write operation or by writing the rwwsre bit in spmcsr. it is also erased after a system reset. note that it is not possible to write more than one time to each address without erasing the temporary buffer. if the eeprom is written in the middle of an spm page load operation, all data loaded will be lost. 26.8.3 performing a page write to execute page write, set up the address in the z-pointer, write ?x0000101? to spmcsr and execute spm within four clock cycles after writing spmcsr. the data in r1 and r0 is ignored. the page address must be written to pcpage. other bits in the z-pointer must be written to zero during this operation. 258 2570n?avr?05/11 atmega325/3250/645/6450 ? page write to the rww section: the nrww section can be read during the page write. ? page write to the nrww section: the cpu is halted during the operation. 26.8.4 using the spm interrupt if the spm interrupt is en abled, the spm interrupt will genera te a constant in terrupt when the spmen bit in spmcsr is cleared. this means th at the interrupt can be used instead of polling the spmcsr register in software. when using the spm interrupt, the interrupt vectors should be moved to the bls section to avoid that an interrupt is accessing the rww section when it is blocked for reading. how to move the interrupts is described in ?interrupts? on page 49 . 26.8.5 consideration while updating bls special care must be taken if the user allows the boot loader section to be updated by leaving boot lock bit11 unprogrammed. an accidental write to the boot loader itself can corrupt the entire boot loader, and further software updates might be impossible. if it is not necessary to change the boot loader software itself, it is recommended to program the boot lock bit11 to protect the boot loader software from any internal software changes. 26.8.6 prevent reading the rww section during self-programming during self-programming (either page erase or page write), the rww section is always blocked for reading. the user software itself must prevent that this section is addressed during the self programming operation. the rwwsb in the spmcsr will be set as long as the rww section is busy. during self-programming the interrupt vector table should be moved to the bls as described in ?interrupts? on page 49 , or the interrupts must be disabled. before addressing the rww section after the programming is completed, the user software must clear the rwwsb by writing the rwwsre. see ?simple assembly code example for a boot loader? on page 260 for an example. 26.8.7 setting the boot loader lock bits by spm to set the boot loader lock bits and general lock bits, write the desired data to r0, write ?x0001001? to spmcsr and execute spm within four clock cycles after writing spmcsr. see table 26-2 and table 26-3 for how the different settings of the boot loader bits affect the flash access. if bits 5..0 in r0 are cleared (zero), the corresponding lock bit will be programmed if an spm instruction is exec uted within four cycles after blbset and spmen are set in spmcsr. the z- pointer is don?t care during this operation, but fo r future compatibility it is recommended to load the z-pointer with 0x0001 (s ame as used for reading the lock bi ts). for future compatibility it is also recommended to set bits 7, and 6 in r0 to ?1? when writing the lock bits. when program- ming the lock bits the entire flas h can be read during the operation. 26.8.8 eeprom write prevents writing to spmcsr note that an eeprom write oper ation will block all software progra mming to flash. reading the fuses and lock bits from software will also be prevented during the eeprom write operation. it is recommended that the user checks the status bit (eewe) in the eecr register and verifies that the bit is cleared before writing to the spmcsr register. bit 76543210 r0 1 1 blb12 blb11 blb02 blb01 lb2 lb1 259 2570n?avr?05/11 atmega325/3250/645/6450 26.8.9 reading the fuse and lock bits from software it is possible to read both the fuse and lock bits from software. to read the lock bits, load the z-pointer with 0x0001 and set the blbset and spmen bits in spmcsr. when an lpm instruc- tion is executed within three cpu cycles after the blbset and spmen bits are set in spmcsr, the value of the lock bits will be loaded in the destination register. the blbset and spmen bits will auto-clear upon completion of reading the lo ck bits or if no lpm instruction is executed within three cpu cycles or no spm instruction is executed within four cpu cycles. when blb- set and spmen are cleared, lpm will work as described in the instruction set manual. the algorithm for reading the fuse low byte is similar to the one described above for reading the lock bits. to read the fuse low byte, load the z-pointer with 0x0000 and set the blbset and spmen bits in spmcsr. when an lpm instruction is executed within three cycles after the blbset and spmen bits are set in the spmcsr, the value of the fuse low byte (flb) will be loaded in the destination register as shown below. refer to table 27-5 on page 267 for a detailed description and mapping of the fuse low byte. similarly, when reading the fuse high byte, load 0x0003 in the z-pointer. when an lpm instruc- tion is executed within three cycles after the blbset and spmen bits are set in the spmcsr, the value of the fuse high byte (fhb) will be load ed in the destination re gister as shown below. refer to table 27-4 on page 267 for detailed description and mapping of the fuse high byte. when reading the extended fuse byte, load 0x0002 in the z-pointer. when an lpm instruction is executed within three cycles after the blbs et and spmen bits are set in the spmcsr, the value of the extended fuse byte (efb) will be loaded in the desti nation register as shown below. refer to table 27-3 on page 266 for detailed description and mapping of the extended fuse byte. fuse and lock bits that are programmed, will be read as zero. fuse and lock bits that are unprogrammed, will be read as one. 26.8.10 preventing flash corruption during periods of low v cc , the flash program can be corrupted because the supply voltage is too low for the cpu and the flash to operate properly. these issues are the same as for board level systems using the flash, and the same design solutions should be applied. a flash program corruption can be caused by two situ ations when the voltage is too low. first, a regular write sequence to the flash requires a minimum voltage to operate correctly. secondly, the cpu itself can execute instruct ions incorrectly, if the supply voltage for executing instructions is too low. flash corruption can easily be avoided by following these design recommendations (one is sufficient): bit 76543210 rd ? ? blb12 blb11 blb02 blb01 lb2 lb1 bit 76543210 rd flb7 flb6 flb5 flb4 flb3 flb2 flb1 flb0 bit 76543210 rd fhb7 fhb6 fhb5 fhb4 fhb3 fhb2 fhb1 fhb0 bit 76543210 rd ? ? ? ? ? efb2efb1efb0 260 2570n?avr?05/11 atmega325/3250/645/6450 1. if there is no need for a boot loader update in the system, program the boot loader lock bits to prevent any boot loader software updates. 2. keep the avr reset active (low) during pe riods of insufficient power supply voltage. this can be done by enabling the internal brown-out detector (bod) if the operating volt- age matches the detection level. if not, an external low v cc reset protection circuit can be used. if a reset occurs while a write operati on is in progress, the write operation will be completed provided that the power supply voltage is sufficient. 3. keep the avr core in power-down sleep mode during periods of low v cc . this will pre- vent the cpu from attempting to decode and execute instructions, effectively protecting the spmcsr register and thus the flash from unintentional writes. 26.8.11 programming time for flash when using spm the calibrated rc oscillator is used to time flash accesses. table 26-5 shows the typical pro- gramming time for flash accesses from the cpu. 26.8.12 simple assembly code example for a boot loader ;-the routine writes one page of data from ram to flash ; the first data location in ram is pointed to by the y pointer ; the first data location in flash is pointed to by the z-pointer ;-error handling is not included ;-the routine must be placed inside the boot space ; (at least the do_spm sub routine). only code inside nrww section can ; be read during self-programming (page erase and page write). ;-registers used: r0, r1, temp1 (r16), temp2 (r17), looplo (r24), ; loophi (r25), spmcrval (r20) ; storing and restoring of registers is not included in the routine ; register usage can be optimized at the expense of code size ;-it is assumed that either the interrupt table is moved to the boot ; loader section or that the interrupts are disabled. .equ pagesizeb = pagesize*2 ;pagesizeb is page size in bytes, not words .org smallbootstart write_page: ; page erase ldi spmcrval, (1< 263 2570n?avr?05/11 atmega325/3250/645/6450 26.9 register description 26.9.1 store program memory control and status register ? spmcsr the store program memory control and status register contains the control bits needed to con- trol the boot loader operations. ? bit 7 ? spmie: spm interrupt enable when the spmie bit is written to one, and the i-bit in the status register is set (one), the spm ready interrupt will be enabled. the spm ready in terrupt will be ex ecuted as long as the spmen bit in the spmcsr register is cleared. ? bit 6 ? rwwsb: read-while-write section busy when a self-programming (page erase or page write) operation to the rww section is initi- ated, the rwwsb will be set (one ) by hardware. when the rwws b bit is set, the rww section cannot be accessed. the rwwsb bit will be cleared if the rwwsre bit is written to one after a self-programming operation is completed. alter natively the rwwsb bit will automatically be cleared if a page load operation is initiated. ? bit 5 ? reserved bit this bit is a reserved bit in the atmel atmega325/3250/645/6450 and always read as zero. ? bit 4 ? rwwsre: read-while-write section read enable when programming (page erase or page write) to the rww section, the rww section is blocked for reading (the rwwsb will be set by hardware). to re-enable the rww section, the user software must wait unt il the programming is complet ed (spmen will be cl eared). then, if the rwwsre bit is written to one at the same time as spmen, the next spm instruction within four clock cycles re-enables the rww secti on. the rww section cannot be re-enabled while the flash is busy with a page erase or a page wr ite (spmen is set). if the rwwsre bit is writ- ten while the flash is being loaded, the flas h load operation will abort and the data loaded will be lost. ? bit 3 ? blbset: boot lock bit set if this bit is written to one at the same time as spmen, the next spm instruction within four clock cycles sets boot lock bits and general lock bits, according to the data in r0. the data in r1 and the address in the z-pointer are ignored. th e blbset bit will automatically be cleared upon completion of the lock bit set, or if no spm instruction is executed within four clock cycles. an lpm instruction within three cycles after blbset and spmen are set in the spmcsr reg- ister, will read either the lock bits or the fuse bits (depending on z0 in the z-pointer) into the destination register. see ?reading the fuse and lock bits from software? on page 259 for details. ? bit 2 ? pgwrt: page write if this bit is written to one at the same time as spmen, the next spm instruction within four clock cycles executes page write, with the data stored in the temporary buffer. the page address is taken from the high part of the z-pointer. the data in r1 and r0 are ignored. the pgwrt bit bit 7 6 5 4 3 2 1 0 spmie rwwsb ? rwwsre blbset pgwrt pgers spmen spmcsr read/write r/w r r r/w r/w r/w r/w r/w initial value 0 0 0 0 0 0 0 0 264 2570n?avr?05/11 atmega325/3250/645/6450 will auto-clear upon co mpletion of a page write, or if no spm instruction is ex ecuted within four clock cycles. the cpu is halted during the ent ire page write operation if the nrww section is addressed. ? bit 1 ? pgers: page erase if this bit is written to one at the same time as spmen, the next spm instruction within four clock cycles executes page erase. the page address is taken from the high part of the z-pointer. the data in r1 and r0 are ignored. the pgers bi t will auto-clear upon comp letion of a page erase, or if no spm instruction is executed within four clock cycles. the cpu is halted during the entire page write operation if the nrww section is addressed. ? bit 0 ? spmen: store program memory enable this bit enables the spm instruction for the next four clock cycles. if written to one together with either rwwsre, blbset, pgwrt? or pgers, t he following spm instruction will have a spe- cial meaning, see description abo ve. if only spmen is written, the following spm instruction will store the value in r1:r0 in the temporary page buffer addressed by the z-pointer. the lsb of the z-pointer is ignored. the spmen bit will aut o-clear upon completion of an spm instruction, or if no spm instruction is executed within four clock cycles. during page erase and page write, the spmen bit remains high until the operation is completed. writing any other combination than ?10001?, ?01001?, ?00101?, ?00011? or ?00001? in the lower five bits will have no effect. 265 2570n?avr?05/11 atmega325/3250/645/6450 27. memory programming 27.1 program and data memory lock bits the atmel atmega325/3250/645/6450 provides six lock bits which can be left unprogrammed (?1?) or can be programmed (?0?) to obtain the additional features listed in table 27-2 . the lock bits can only be erased to ?1? with the chip erase command. note: 1. ?1? means unprogrammed, ?0? means programmed table 27-1. lock bit byte (1) lock bit byte bit no description default value 7 ? 1 (unprogrammed) 6 ? 1 (unprogrammed) blb12 5 boot lock bit 1 (unprogrammed) blb11 4 boot lock bit 1 (unprogrammed) blb02 3 boot lock bit 1 (unprogrammed) blb01 2 boot lock bit 1 (unprogrammed) lb2 1 lock bit 1 (unprogrammed) lb1 0 lock bit 1 (unprogrammed) table 27-2. lock bit protection modes (1)(2) memory lock bits protection type lb mode lb2 lb1 1 1 1 no memory lock features enabled. 210 further programming of the flash and eeprom is disabled in parallel and serial programming mode. the fuse bits are locked in both serial and parallel programming mode. (1) 300 further programming and verification of the flash and eeprom is disabled in parall el and serial programming mode. the boot lock bits and fuse bits are locked in both serial and parallel programming mode. (1) blb0 mode blb02 blb01 111 no restrictions for spm or lpm accessing the application section. 2 1 0 spm is not allowed to write to the application section. 300 spm is not allowed to write to the application section, and lpm executing from the boot loader section is not allowed to read from the application section. if interrupt vectors are placed in the boot loader section, interrupts are disabled while executing from the application section. 401 lpm executing from the boot loader section is not allowed to read from the application section. if interrupt vectors are placed in the boot loader section, interrupts are disabled while executing from the application section. 266 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. program the fuse bits and boot lock bits before programming the lb1 and lb2. 2. ?1? means unprogrammed, ?0? means programmed 27.2 fuse bits the atmel atmega325/3250/645/6450 has three fuse bytes. table 27-3 - table 27-5 describe briefly the functionality of all the fuses and how they are mapped into the fuse bytes. note that the fuses are read as logical zero, ?0?, if they are programmed. note: 1. see table 2 8 -5 on page 301 for bodlevel fuse decoding. 2. port g, pg5 is input only. pull-up is always on. see ?alternate functions of port g? on page 76. blb1 mode blb12 blb11 111 no restrictions for spm or lpm accessing the boot loader section. 2 1 0 spm is not allowed to write to the boot loader section. 300 spm is not allowed to write to the boot loader section, and lpm executing from the application section is not allowed to read from the boot loader section. if interrupt vectors are placed in the application section, interrupts are disabled while executing from the boot loader section. 401 lpm executing from the application section is not allowed to read from the boot loader se ction. if interrupt vectors are placed in the application section, interrupts are disabled while executing from the boot loader section. table 27-2. lock bit protection modes (1)(2) (continued) memory lock bits protection type table 27-3. extended fuse byte extended fuse byte bit no description default value ?7? 1 ?6? 1 ?5? 1 ?4? 1 ?5? 1 bodlevel1 (1) 2 brown-out detector trigger level 1 (unprogrammed) bodlevel0 (1) 1 brown-out detector trigger level 1 (unprogrammed) rstdisbl (2) 0 external reset disable 1 (unprogrammed) 267 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. the spien fuse is not accessible in serial programming mode. 2. the default value of bootsz1..0 results in maximum boot size. see table 26-6 on page 262 for details. 3. see ?register description? on page 47 for details. 4. never ship a product with the ocden fuse prog rammed regardless of the setting of lock bits and jtagen fuse. a programmed ocden fuse en ables some parts of the clock system to be running in all sleep modes. this may increase the power consumption. 5. if the jtag interface is left unconnected, the jt agen fuse should if possible be disabled. this to avoid static current at the tdo pin in the jtag interface. note: 1. the default value of sut1..0 results in maximum start-up time for the default clock source. see table 2 8 -4 on page 301 for details. 2. the default setting of cksel3..0 results in internal rc oscillator @ 8 mhz. see table 9-5 on page 29 for details. 3. the ckout fuse allow the system cl ock to be output on porte7. see ?clock output buffer? on page 31 for details. 4. see ?system clock prescaler? on page 32 for details. table 27-4. fuse high byte fuse high byte bit no description default value ocden (4) 7 enable ocd 1 (unprogrammed, ocd disabled) jtagen (5) 6 enable jtag 0 (programmed, jtag enabled) spien (1) 5 enable serial program and data downloading 0 (programmed, spi prog. enabled) wdton (3) 4 watchdog timer always on 1 (unprogrammed) eesave 3 eeprom memory is preserved through the chip erase 1 (unprogrammed, eeprom not preserved) bootsz1 2 select boot size (see table 27-6 for details) 0 (programmed) (2) bootsz0 1 select boot size (see table 27-6 for details) 0 (programmed) (2) bootrst 0 select reset vector 1 (unprogrammed) table 27-5. fuse low byte fuse low byte bit no description default value ckdiv 8 (4) 7 divide clock by 8 0 (programmed) ckout (3) 6 clock output 1 (unprogrammed) sut1 5 select start-up time 1 (unprogrammed) (1) sut0 4 select start-up time 0 (programmed) (1) cksel3 3 select clock source 0 (programmed) (2) cksel2 2 select clock source 0 (programmed) (2) cksel1 1 select clock source 1 (unprogrammed) (2) cksel0 0 select clock source 0 (programmed) (2) 268 2570n?avr?05/11 atmega325/3250/645/6450 the status of the fuse bits is not affected by chip erase. note that the fuse bits are locked if lock bit1 (lb1) is programmed. program the fuse bits before programming the lock bits. 27.2.1 latching of fuses the fuse values are latched when the device enters programming mode and changes of the fuse values will have no effect until the part leaves programming mode. this does not apply to the eesave fuse which will take effect once it is programmed. the fuse s are also latched on power-up in normal mode. 27.3 signature bytes all atmel microcontrollers have a three-byte signature code which identifies the device. this code can be read in both serial and parallel mode, also when the device is locked. the three bytes reside in a separate address space. for the atmel atmega325/3250/645/6450 the signature bytes are: 1. 0x000: 0x1e (indicates manufactured by atmel). 2. 0x001: 0x95/0x96 (indicates flash memory,refer to ?part number? on page 225 ). 3. 0x002: 0x05/0x06 (indicates device, refer to ?part number? on page 225 ). 27.4 calibration byte the atmel atmega325/3250/645/6450 has a byte calibration value for the internal rc oscilla- tor. this byte resides in t he high byte of address 0x000 in the signature address space. during reset, this byte is automatically written into the osccal register to ensure correct frequency of the calibrated rc oscillator. 27.5 parallel programming paramete rs, pin mapping, and commands this section describes how to parallel program and verify flash program memory, eeprom data memory, memory lock bits, and fuse bits in the atmel atmega325/3250/645/6450. pulses are assumed to be at least 250ns unless otherwise noted. 27.5.1 signal names in this section, some pins of the atmel atmega325/3250/645/6450 are referenced by signal names describing their functionality during parallel programming, see figure 27-1 and table 27- 6 . pins not described in the following table are referenced by pin names. the xa1/xa0 pins determine the action executed when the xtal1 pin is given a positive pulse. the bit coding is shown in table 27- 8 . when pulsing wr or oe , the command loaded determines the action executed. the different commands are shown in table 27-9 . 269 2570n?avr?05/11 atmega325/3250/645/6450 figure 27-1. parallel programming table 27-6. pin name mapping signal name in programming mode pin name i/o function rdy/bsy pd1 o 0: device is busy programming, 1: device is ready for new command. oe pd2 i output enable (active low). wr pd3 i write pulse (active low). bs1 pd4 i byte select 1 (?0? selects low byte, ?1? selects high byte). xa0 pd5 i xtal action bit 0 xa1 pd6 i xtal action bit 1 pagel pd7 i program memory and eeprom data page load. bs2 pa0 i byte select 2 (?0? selects low byte, ?1? selects 2?nd high byte). data pb7-0 i/o bi-directional data bus (output when oe is low). table 27-7. pin values used to enter programming mode pin symbol value pagel prog_enable[3] 0 xa1 prog_enable[2] 0 xa0 prog_enable[1] 0 bs1 prog_enable[0] 0 vcc +5v gnd xtal1 pd1 pd2 pd3 pd4 pd5 pd6 pb7 - pb0 data reset pd7 +12 v bs1 xa0 xa1 oe rdy/bsy pagel pa0 wr bs2 avcc +5v 270 2570n?avr?05/11 atmega325/3250/645/6450 table 27-8. xa1 and xa0 coding xa1 xa0 action when xtal1 is pulsed 0 0 load flash or eeprom addre ss (high or low address byte determined by bs1). 0 1 load data (high or low data byte for flash determined by bs1). 1 0 load command 1 1 no action, idle table 27-9. command byte bit coding command byte command executed 1000 0000 chip erase 0100 0000 write fuse bits 0010 0000 write lock bits 0001 0000 write flash 0001 0001 write eeprom 0000 1000 read signature bytes and calibration byte 0000 0100 read fuse and lock bits 0000 0010 read flash 0000 0011 read eeprom table 27-10. no. of words in a page and no. of pages in the flash flash size page size pcword no. of pages pcpage pcmsb 16/32k words (32/64k bytes) 64/12 8 words pc[5/6:0] 256 pc [13/14:6/7] 13/14 table 27-11. no. of words in a page and no. of pages in the eeprom eeprom size page size pcword no. of pages pcpage eeamsb 1k/2k bytes 4/ 8 bytes eea[1/2:0] 256 eea [13/14:2/3] 13/14 271 2570n?avr?05/11 atmega325/3250/645/6450 27.6 parallel programming 27.6.1 enter programming mode the following algorithm puts the device in parallel (high-voltage) programming mode: 1. set prog_enable pins listed in table 27-7 on page 269 to ?0000?, reset pin and v cc to 0v. 2. apply 4.5 - 5.5v between v cc and gnd. 3. ensure that v cc reaches at least 1. 8 v within the next 20 s. 4. wait 20 - 60 s, and apply 11.5 - 12.5v to reset. 5. keep the prog_enable pins unchanged for at least 10s after the high-voltage has been applied to ensure the prog_enable signature has been latched. 6. wait at least 300 s before giving any parallel programming commands. 7. exit programming mode by power the device down or by bringing reset pin to 0v. if the rise time of the v cc is unable to fulfill the requiremen ts listed above, th e following alterna- tive algorithm can be used. 1. set prog_enable pins listed in table 27-7 on page 269 to ?0000?, reset pin to 0v and v cc to 0v. 2. apply 4.5 - 5.5v between v cc and gnd. 3. monitor v cc , and as soon as v cc reaches 0.9 - 1.1v, appl y 11.5 - 12.5v to reset. 4. keep the prog_enable pins unchanged for at least 10s after the high-voltage has been applied to ensure the prog_enable signature has been latched. 5. wait until v cc actually reaches 4.5 -5.5v before giving any parallel programming commands. 6. exit programming mode by power the device down or by bringing reset pin to 0v. 27.6.2 considerations for efficient programming the loaded command and address are retained in the device during programming. for efficient programming, the following should be considered. ? the command needs only be loaded once when writing or reading multiple memory locations. ? skip writing the data value 0xff, that is t he contents of the enti re eeprom (unless the eesave fuse is programmed) and flash after a chip erase. ? address high byte needs only be loaded before programming or reading a new 256 word window in flash or 256 byte eeprom. this consideration also applies to signature bytes reading. 27.6.3 chip erase the chip erase will erase the flash and eeprom (1) memories plus lock bits. the lock bits are not reset until the program memory has been completely erased. the fuse bits are not changed. a chip erase must be perfor med before the flas h and/or eeprom are reprogrammed. note: 1. the eeprpom memory is preserved duri ng chip erase if the eesave fuse is programmed. load command ?chip erase? 272 2570n?avr?05/11 atmega325/3250/645/6450 1. set xa1, xa0 to ?10?. this enables command loading. 2. set bs1 to ?0?. 3. set data to ?1000 0000?. this is the command for chip erase. 4. give xtal1 a positive pulse. this loads the command. 5. give wr a negative pulse. this starts the chip erase. rdy/bsy goes low. 6. wait until rdy/bsy goes high before loading a new command. 27.6.4 programming the flash the flash is organized in pages, see table 27-10 on page 270 . when programming the flash, the program data is latched into a page buffer. this allows one page of program data to be pro- grammed simultaneously. the following procedure describes how to program the entire flash memory: a. load command ?write flash? 1. set xa1, xa0 to ?10?. this enables command loading. 2. set bs1 to ?0?. 3. set data to ?0001 0000?. this is the command for write flash. 4. give xtal1 a positive pulse. this loads the command. b. load address low byte 1. set xa1, xa0 to ?00?. this enables address loading. 2. set bs1 to ?0?. this selects low address. 3. set data = address low byte (0x00 - 0xff). 4. give xtal1 a positive pulse. this loads the address low byte. c. load data low byte 1. set xa1, xa0 to ?01?. this enables data loading. 2. set data = data low byte (0x00 - 0xff). 3. give xtal1 a positive pulse. this loads the data byte. d. load data high byte 1. set bs1 to ?1?. this selects high data byte. 2. set xa1, xa0 to ?01?. this enables data loading. 3. set data = data high byte (0x00 - 0xff). 4. give xtal1 a positive pulse. this loads the data byte. e. latch data 1. set bs1 to ?1?. this selects high data byte. 2. give pagel a positive pulse. this latches the data bytes. (see figure 27-3 for signal waveforms) f. repeat b through e until the entire buffer is filled or until all data within the page is loaded. while the lower bits in the address are mapped to words within the page, the higher bits address the pages within the flash . this is illustrated in figure 27-2 on page 273 . note that if less than eight bits are required to address words in the page (pagesize < 256), the most significant bit(s) in the address low byte are used to address the page when performing a page write. g. load address high byte 273 2570n?avr?05/11 atmega325/3250/645/6450 1. set xa1, xa0 to ?00?. this enables address loading. 2. set bs1 to ?1?. this selects high address. 3. set data = address high byte (0x00 - 0xff). 4. give xtal1 a positive pulse. this loads the address high byte. h. program page 1. give wr a negative pulse. this starts programming of the entire page of data. rdy/bsy goes low. 2. wait until rdy/bsy goes high (see figure 27-3 for signal waveforms). i. repeat b through h until the entire flash is programmed or until all data has been programmed. j. end page programming 1. 1. set xa1, xa0 to ?10?. this enables command loading. 2. set data to ?0000 0000?. this is the command for no operation. 3. give xtal1 a positive pulse. this loads the command, and the internal write signals are reset. figure 27-2. addressing the flash which is organized in pages (1) note: 1. pcpage and pcword are listed in table 27-10 on page 270 . program memory word address within a page page address within the flash instruction word pag e pcword[pagemsb:0]: 00 01 02 pageend pag e pcword pcpage pcmsb pagemsb program counter 274 2570n?avr?05/11 atmega325/3250/645/6450 figure 27-3. programming the flash waveforms (1) note: 1. ?xx? is don?t care. the letters re fer to the programming description above. 27.6.5 programming the eeprom the eeprom is organized in pages, see table 27-11 on page 270 . when programming the eeprom, the program data is latche d into a page buffer. this al lows one page of data to be programmed simultaneously. th e programming algorithm for th e eeprom data memory is as follows (refer to ?programming the flash? on page 272 for details on command, address and data loading): 1. a: load command ?0001 0001?. 2. g: load address high byte (0x00 - 0xff). 3. b: load address low byte (0x00 - 0xff). 4. c: load data (0x00 - 0xff). 5. e: latch data (give pagel a positive pulse). k: repeat 3 through 5 until the entire buffer is filled. l: program eeprom page 1. set bs1 to ?0?. 2. give wr a negative pulse. this starts pr ogramming of the eeprom page. rdy/bsy goes low. 3. wait until to rdy/bsy goes high before programming the next page (see figure 27-4 for signal waveforms). rdy/bsy wr oe reset +12v pagel bs2 0x10 addr. low addr. high data data low data high addr. low data low data high xa1 xa0 bs1 xtal1 xx xx xx abcdeb cdegh f 275 2570n?avr?05/11 atmega325/3250/645/6450 figure 27-4. programming the eeprom waveforms 27.6.6 reading the flash the algorithm for reading the flash memory is as follows (refer to ?programming the flash? on page 272 for details on command and address loading): 1. a: load command ?0000 0010?. 2. g: load address high byte (0x00 - 0xff). 3. b: load address low byte (0x00 - 0xff). 4. set oe to ?0?, and bs1 to ?0?. the flash word low byte can now be read at data. 5. set bs1 to ?1?. the flash word high byte can now be read at data. 6. set oe to ?1?. 27.6.7 reading the eeprom the algorithm for reading the eeprom memory is as follows (refer to ?programming the flash? on page 272 for details on command and address loading): 1. a: load command ?0000 0011?. 2. g: load address high byte (0x00 - 0xff). 3. b: load address low byte (0x00 - 0xff). 4. set oe to ?0?, and bs1 to ?0?. the eeprom data byte can now be read at data. 5. set oe to ?1?. 27.6.8 programming the fuse low bits the algorithm for programming the fuse low bits is as follows (refer to ?programming the flash? on page 272 for details on command and data loading): 1. a: load command ?0100 0000?. 2. c: load data low byte. bit n = ?0? programs and bit n = ?1? erases the fuse bit. 3. give wr a negative pulse and wait for rdy/bsy to go high. 27.6.9 programming the fuse high bits the algorithm for programming the fuse high bits is as follows (refer to ?programming the flash? on page 272 for details on command and data loading): rdy/bsy wr oe reset +12v pagel bs2 0x11 addr. high data addr. low data addr. low data xx xa1 xa0 bs1 xtal1 xx agbceb c el k 276 2570n?avr?05/11 atmega325/3250/645/6450 1. a: load command ?0100 0000?. 2. c: load data low byte. bit n = ?0? programs and bit n = ?1? erases the fuse bit. 3. set bs1 to ?1? and bs2 to ?0?. this selects high data byte. 4. give wr a negative pulse and wait for rdy/bsy to go high. 5. set bs1 to ?0?. this selects low data byte. 27.6.10 programming the extended fuse bits the algorithm for programming the extended fuse bits is as follows (refer to ?programming the flash? on page 272 for details on command and data loading): 1. 1. a: load command ?0100 0000?. 2. 2. c: load data low byte. bit n = ?0? programs and bit n = ?1? erases the fuse bit. 3. 3. set bs1 to ?0? and bs2 to ?1?. this selects extended data byte. 4. 4. give wr a negative pulse and wait for rdy/bsy to go high. 5. 5. set bs2 to ?0?. this selects low data byte. figure 27-5. programming the fuses waveforms 27.6.11 programming the lock bits the algorithm for programming the lock bits is as follows (refer to ?programming the flash? on page 272 for details on command and data loading): 1. a: load command ?0010 0000?. 2. c: load data low byte. bit n = ?0? programs the lock bit. if lb mode 3 is programmed (lb1 and lb2 is programmed), it is not possible to program the boot lock bits by any external programming mode. 3. give wr a negative pulse and wait for rdy/bsy to go high. the lock bits can only be cleared by executing chip erase. 27.6.12 reading the fuse and lock bits the algorithm for reading the fuse and lock bits is as follows (refer to ?programming the flash? on page 272 for details on command loading): rdy/bsy wr oe reset +12v pagel 0x40 data data xx xa1 xa0 bs1 xtal1 ac 0x40 data xx ac write fuse low byte write fuse high byte 0x40 data xx ac write extended fuse byte bs2 277 2570n?avr?05/11 atmega325/3250/645/6450 1. a: load command ?0000 0100?. 2. set oe to ?0?, bs2 to ?0? and bs1 to ?0?. the status of the fuse low bits can now be read at data (?0? means programmed). 3. set oe to ?0?, bs2 to ?1? and bs1 to ?1?. the status of the fuse high bits can now be read at data (?0? means programmed). 4. set oe to ?0?, bs2 to ?1?, and bs1 to ?0?. the status of the extended fuse bits can now be read at data (?0? means programmed). 5. set oe to ?0?, bs2 to ?0? and bs1 to ?1?. the status of the lock bits can now be read at data (?0? means programmed). 6. set oe to ?1?. figure 27-6. mapping between bs1, bs2 and the fuse and lock bits during read 27.6.13 reading the signature bytes the algorithm for reading the signatur e bytes is as follows (refer to ?programming the flash? on page 272 for details on command and address loading): 1. a: load command ?0000 1000?. 2. b: load address low byte (0x00 - 0x02). 3. set oe to ?0?, and bs1 to ?0?. the selected signature byte can now be read at data. 4. set oe to ?1?. 27.6.14 reading the calibration byte the algorithm for reading the calibration byte is as follows (refer to ?programming the flash? on page 272 for details on command and address loading): 1. a: load command ?0000 1000?. 2. b: load address low byte, 0x00. 3. set oe to ?0?, and bs1 to ?1?. the calibration byte can now be read at data. 4. set oe to ?1?. lock bits 0 1 bs2 fuse high byte 0 1 bs1 data fuse low byte 0 1 bs2 extended fuse byte 278 2570n?avr?05/11 atmega325/3250/645/6450 27.6.15 parallel programming characteristics figure 27-7. parallel programming timing, including some general timing requirements figure 27-8. parallel programming timing, loading sequence with timing requirements (1) note: 1. the timing requirements shown in figure 27-7 (i.e., t dvxh , t xhxl , and t xldx ) also apply to load- ing operation. data & contol (data, xa0/1, bs1, bs2) xtal1 t xhxl t wlwh t dvxh t xldx t plwl t wlrh wr rdy/bsy pagel t phpl t plbx t bvph t xlwl t wlbx t bvwl wlrl xtal1 pagel t plxh xlxh t t xlph addr0 (low byte) data (low byte) data (high byte) addr1 (low byte) data bs1 xa0 xa1 load address (low byte) load data (low byte) load data (high byte) load data load address (low byte) 279 2570n?avr?05/11 atmega325/3250/645/6450 figure 27-9. parallel programming timing, reading sequence (within the same page) with timing requirements (1) note: 1. the timing requirements shown in figure 27-7 (i.e., t dvxh , t xhxl , and t xldx ) also apply to read- ing operation. table 27-12. parallel programming characteristics, v cc = 5v 10% symbol parameter min typ max units v pp programming enable voltage 11.5 12.5 v i pp programming enable current 250 a t dvxh data and control valid before xtal1 high 67 ns t xlxh xtal1 low to xtal1 high 200 ns t xhxl xtal1 pulse width high 150 ns t xldx data and control hold after xtal1 low 67 ns t xlwl xtal1 low to wr low 0 ns t xlph xtal1 low to pagel high 0 ns t plxh pagel low to xtal1 high 150 ns t bvph bs1 valid before pagel high 67 ns t phpl pagel pulse width high 150 ns t plbx bs1 hold after pagel low 67 ns t wlbx bs2/1 hold after wr low 67 ns t plwl pagel low to wr low 67 ns t bvwl bs1 valid to wr low 67 ns t wlwh wr pulse width low 150 ns t wlrl wr low to rdy/bsy low 0 1 s t wlrh wr low to rdy/bsy high (1) 3.7 4.5 ms t wlrh_ce wr low to rdy/bsy high for chip erase (2) 7.5 9 ms t xlol xtal1 low to oe low 0 ns xtal1 oe addr0 (low byte) data (low byte) data (high byte) addr1 (low byte) data bs1 xa0 xa1 load address (low byte) read data (low byte) read data (high byte) load address (low byte) t bvdv t oldv t xlol t ohdz 280 2570n?avr?05/11 atmega325/3250/645/6450 notes: 1. t wlrh is valid for the write flash, write eepro m, write fuse bits and write lock bits commands. 2. t wlrh_ce is valid for the chip erase command. 27.7 serial downloading both the flash and eeprom memo ry arrays can be programmed using the serial spi bus while reset is pulled to gnd. the serial interface consists of pins sck, mosi (input) and miso (out- put). after reset is set low, the programming enable instruction needs to be executed first before program/erase operations can be executed. note, in table 27-13 on page 2 8 0 , the pin mapping for spi programming is listed. not all pa rts use the spi pins dedicated for the internal spi interface. 27.7.1 serial programming pin mapping figure 27-10. serial programming and verify (1) notes: 1. if the device is clocked by the internal oscill ator, it is no need to connect a clock source to the xtal1 pin. 2. v cc - 0.3v < avcc < v cc + 0.3v, however, avcc should always be within 1. 8 - 5.5v when programming the eeprom, an auto-erase cycle is built into the self-timed programming operation (in the serial mode only) and there is no need to first execute the chip erase instruction. the chip erase operation turns the content of every memory location in both the program and eeprom arrays into 0xff. depending on cksel fuses, a valid clock must be present. the minimum low and high periods for the serial clock (sck) input are defined as follows: t bvdv bs1 valid to data valid 0 250 ns t oldv oe low to data valid 250 ns t ohdz oe high to data tri-stated 250 ns table 27-12. parallel programming characteristics, v cc = 5v 10% (continued) symbol parameter min typ max units table 27-13. pin mapping serial programming symbol pins i/o description mosi pb2 i serial data in miso pb3 o serial data out sck pb1 i serial clock vcc gnd xtal1 sck miso mosi reset +1. 8 - 5.5v avcc +1. 8 - 5.5v (2) 281 2570n?avr?05/11 atmega325/3250/645/6450 low: > 2 cpu clock cycles for f ck < 12 mhz, 3 cpu clock cycles for f ck >= 12 mhz high: > 2 cpu clock cycles for f ck < 12 mhz, 3 cpu clock cycles for f ck >= 12 mhz 27.7.2 serial programming algorithm when writing serial data to the atmel atmega 325/3250/645/6450, data is clocked on the rising edge of sck. when reading data from the at mel atmega325/3250/645/6450, da ta is clocked on the falling edge of sck. see figure 27-11 for timing details. to program and verify the atmel atmega325/3250/645/6450 in the serial programming mode, the following sequence is recommended (see four byte instruction formats in table 27-15 ): 1. power-up sequence: apply power between v cc and gnd while reset and sck are set to ?0?. in some sys- tems, the programmer can not guarantee that sck is held low during power-up. in this case, reset must be given a positive pulse of at least two cpu clock cycles duration after sck has been set to ?0?. 2. wait for at least 20ms and enable serial programming by sending the programming enable serial instruction to pin mosi. 3. the serial programming instructions will not wo rk if the communication is out of synchro- nization. when in sync. the se cond byte (0x53), will echo back when issuing the third byte of the programming enable instruction. whether the echo is correct or not, all four bytes of the instruction must be transmitted. if the 0x53 did not echo back, give reset a positive pulse and issue a new programming enable command. 4. the flash is programmed one page at a time. the page size is found in table 27-10 on page 270 . the memory page is loaded one byte at a time by supplying the 6/7 lsb of the address and data together with the load program memory page instruction. to ensure correct loading of the page, the data low byte must be loaded before data high byte is applied for a given address. the program memory page is stored by loading the write program memory page instruction with the 8 msb of the address. if polling is not used, the user must wait at least t wd_flash before issuing the next page. (see table 27-14 .) accessing the serial programming interface before the flash write operation completes can result in incorrect programming. 5. a : the eeprom array is programm ed one byte at a time by supplying th e address and data together with the appropria te write instruction. an eeprom memory location is first automatically erased before new data is written. if polling (rdy/bsy ) is not used, the user must wait at least t wd_eeprom before issuing the next byte (see table 27-14 .) in a chip erased device, no 0xffs in the data file(s) need to be programmed. b : the eeprom array is programmed one page at a time. the memory page is loaded one byte at a time by supplying the 2 lsb of the address and data together with the load eeprom memory page instruction. the eeprom memory page is stored by loading the write eeprom memory page instruction with the 4 msb of the address. when using eeprom page access only byte locations loaded with the load eeprom memory page instruction is altered. th e remaining locations remain unchanged. if polling (rdy/bsy ) is not used, the used must wait at least t wd_eeprom before issuing the next page (see table 27-11 ). in a chip erased device, no 0xff in the data file(s) need to be programmed. 6. any memory location can be verified by using the read instruction which returns the con- tent at the selected address at serial output miso. 7. at the end of the programming session, reset can be set high to commence normal operation. 282 2570n?avr?05/11 atmega325/3250/645/6450 8 . power-off sequence (if needed): set reset to ?1?. tu r n v cc power off. figure 27-11. serial programming waveforms 27.7.3 serial programming instruction set table 27-15 and figure 27-12 on page 2 8 4 describes the instruction set. table 27-14. minimum wait delay before writing the next flash or eeprom location symbol minimum wait delay t wd_fuse 4.5ms t wd_flash 4.5ms t wd_eeprom 9.0ms t wd_erase 9.0ms msb msb lsb lsb serial clock input (sck) serial data input (mosi) (miso) sample serial data output table 27-15. serial programming instruction set instruction/operation instruction format byte 1 byte 2 byte 3 byte4 programming enable $ac $53 $00 $00 chip erase (program memory/eeprom) $ac $ 8 0 $00 $00 poll rdy/bsy $f0 $00 $00 data byte out load instructions load extended address byte (1) $4d $00 extended adr $00 load program memory page, high byte $4 8 $00 adr lsb high data byte in load program memory page, low byte $40 $00 adr lsb low data byte in load eeprom memory page (page access) $c1 $00 0000 00aa / 0000 0aaa data byte in read instructions read program memory, high byte $2 8 adr msb adr lsb high data byte out read program memory, low byte $20 adr msb adr lsb low data byte out read eeprom memory $a0 0000 00aa / 0000 0aaa aaaa aaaa data byte out 283 2570n?avr?05/11 atmega325/3250/645/6450 notes: 1. not all instructions are applicable for all parts 2. a = address 3. bits are programmed ?0?, unprogrammed ?1?. 4. to ensure future compatibility, unused fuses and lock bits should be unprogrammed (?1?) . 5. refer to the correspondig section for fuse and lock bits, calibration and signature bytes and page size. 6. see htt://www.atmel.com/avr for application notes regarding programming and programmers. if the lsb in rdy/bsy data byte out is ?1?, a pr ogramming operation is still pending. wait until this bit returns ?0? before the ne xt instruction is carried out. within the same page, the low data byte must be loaded prior to the high data byte. after data is loaded to the page buffer, program the eeprom page, see figure 27-12 . read lock bits $5 8 $00 $00 data byte out read signature byte $30 $00 0000 000aa data byte out read fuse bits $50 $00 $00 data byte out read fuse high bits $5 8 $0 8 $00 data byte out read extended fuse bits $50 $0 8 $00 data byte out read calibration byte $3 8 $00 $00 data byte out write instructions write program memory page $4c adr msb adr lsb $00 write eeprom memory $c0 0000 00aa / 0000 0aaa aaaa aaaa data byte in write eeprom memory page (page access) $c2 0000 00aa / 0000 0aaa aaaa aa00 / aaaa a000 $00 write lock bits $ac $e0 $00 data byte in write fuse bits $ac $a0 $00 data byte in write fuse high bits $ac $a 8 $00 data byte in write extended fuse bits $ac $a4 $00 data byte in table 27-15. serial programming instruction set instruction/operation instruction format byte 1 byte 2 byte 3 byte4 284 2570n?avr?05/11 atmega325/3250/645/6450 figure 27-12. serial programming instruction example 27.7.4 spi serial programming characteristics for characteristics of the spi module see ?spi timing characteristics? on page 302. 27.8 programming via the jtag interface programming through the jtag interface requires control of the four jtag specific pins: tck, tms, tdi, and tdo. control of the reset and clock pins is not required. to be able to use the jtag interface, the jtagen fuse must be programmed. the device is default shipped with the fuse programmed. in addition, the jtd bit in mcucsr must be cleared. alternatively, if the jtd bit is set, the external reset can be fo rced low. then, the jtd bit will be cleared after two chip clocks, and the jtag pins are available for programming. this provides a means of using the jtag pins as normal port pi ns in running mode while still allowing in-sys- tem programming via the jtag interface. note th at this technique can not be used when using the jtag pins for boundary-scan or on-chip debug. in these cases the jtag pins must be ded- icated for this purpose. during programming the clock frequency of the tck input must be less than the maximum fre- quency of the chip. the system clock prescaler can not be used to divide the tck clock input into a sufficiently low frequency. as a definition in this data sheet, the lsb is shifted in and out first of all shift registers. byte 1 byte 2 byte 3 byte 4 adr lsb bit 15 b 0 serial programming instruction program memory/ eeprom memory page 0 page 1 page 2 page n-1 page buffer write program memory page/ write eeprom memory page load program memory page (high/low byte)/ load eeprom memory page (page access) byte 1 byte 2 byte 3 byte 4 bit 15 b 0 adr msb page offset page number ad r m ms sb a a adr r l lsb b 285 2570n?avr?05/11 atmega325/3250/645/6450 27.8.1 programming specific jtag instructions the instruction register is 4-bit wide, supporting up to 16 instructions. the jtag instructions useful for programming are listed below. the opcode for each instruction is shown behind the instruction name in hex format. the text describes which data register is selected as path between tdi and tdo for each instruction. the run-test/idle state of the tap controller is used to generate internal clocks. it can also be used as an idle state between jtag sequences . the state machine sequence for changing the instruction word is shown in figure 27-13 . figure 27-13. state machine sequence for changing the instruction word 27.8.2 avr_reset (0xc) the avr specific public jtag in struction for setting the avr device in the reset mode or taking the device out from the reset mode. the tap controller is not reset by this instruction. the one bit reset register is selected as data register. no te that the reset will be active as long as there is a logic ?one? in the reset chain. the output from this chain is not latched. the active states are: ? shift-dr: the reset register is shifted by the tck input. test-logic-reset run-test/idle shift-dr exit1-dr pause-dr exit2-dr update-dr select-ir scan capture-ir shift-ir exit1-ir pause-ir exit2-ir update-ir select-dr scan capture-dr 0 1 0 11 1 00 00 11 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 0 0 1 1 286 2570n?avr?05/11 atmega325/3250/645/6450 27.8.3 prog_enable (0x4) the avr specific public jtag instruction for enabling programming via the jtag port. the 16- bit programming enable register is selected as data register. the active states are the following: ? shift-dr: the programming enable signature is shifted into the data register. ? update-dr: the programming enable signature is compared to the correct value, and programming mode is entered if the signature is valid. 27.8.4 prog_commands (0x5) the avr specific public jtag instruction for entering programming commands via the jtag port. the 15-bit programming command register is selected as data register. the active states are the following: ? capture-dr: the result of the previous command is loaded into the data register. ? shift-dr: the data register is shifted by the tck input, shifting out the result of the previous command and shifting in the new command. ? update-dr: the programming command is applied to the flash inputs ? run-test/idle: one clock cycle is generated, executing the applied command (not always required, see table 27-16 below). 27.8.5 prog_pageload (0x6) the avr specific public jtag instruction to directly load the flash data page via the jtag port. an 8 -bit flash data byte register is selected as the data register. this is physically the 8 lsbs of the programming command register. the active states are the following: ? shift-dr: the flash data byte register is shifted by the tck input. ? update-dr: the content of the flash data byte register is copied into a temporary register. a write sequence is initiated that within 11 tck cycles loads the content of the temporary register into the flash page buffer. the avr automatically alternates between writing the low and the high byte for each new update-dr state, starting with the low byte for the first update-dr encountered after entering the prog_pageload command. the program counter is pre-incremented before writing the low byte, except fo r the first written byte. this ensures that the first data is written to the address set up by prog_commands, and loading the last location in the page buffer does not make the program counter increment into the next page. 27.8.6 prog_pageread (0x7) the avr specific public jtag instruction to dire ctly capture the flash content via the jtag port. an 8 -bit flash data byte register is selected as the data register. this is physically the 8 lsbs of the programming command register. the active states are the following: ? capture-dr: the content of the selected flash byte is captured into the flash data byte register. the avr automatically alternates between reading the low and the high byte for each new capture-dr state, starting with the low byte for the first capture-dr encountered after entering the prog_pageread command. the program counter is post-incremented after reading each high byte, including the first read byte. this ensures that the first data is captured from the first address set up by prog_commands, and reading the last location in the page makes the program counter increment into the next page. ? shift-dr: the flash data byte register is shifted by the tck input. 287 2570n?avr?05/11 atmega325/3250/645/6450 27.8.7 data registers the data registers are selected by the jtag instruction registers described in section ?pro- gramming specific jtag instructions? on page 2 8 5 . the data registers relevant for programming operations are: ? reset register ? programming enable register ? programming command register ? flash data byte register 27.8.8 reset register the reset register is a test data register used to reset the part during programming. it is required to reset the part before entering programming mode. a high value in the reset register corresponds to pulling the external reset low. the part is reset as long as there is a high value present in t he reset register. depending on the fuse settings for the clock options, the part will remain reset for a re set time-out period (refer to ?clock sources? on page 27 ) after releasing the reset register. the output from this data register is not latched, so the reset will take place immediately, as shown in figure 25-2 on page 226 . 27.8.9 programming enable register the programming enable register is a 16-bit regist er. the contents of this register is compared to the programming enable signature, binary code 0b1010_0011_0111_0000. when the con- tents of the register is equal to the programming enable signature, programming via the jtag port is enabled. the register is reset to 0 on power-on reset, and should always be reset when leaving programming mode. figure 3. programming enable register 27.8.10 programming command register the programming command register is a 15-bit regist er. this register is us ed to serially shift in programming commands, and to serially shift out the result of the previous command, if any. the jtag programming instruction set is shown in table 27-16 . the state sequence when shifting in the programming comma nds is illustrated in figure 27-15 . tdi tdo d a t a = dq clockdr & prog_enable programming enable 0xa370 288 2570n?avr?05/11 atmega325/3250/645/6450 figure 27-14. programming command register tdi tdo s t r o b e s a d d r e s s / d a t a flash eeprom fuses lock bits 289 2570n?avr?05/11 atmega325/3250/645/6450 table 27-16. jtag programming instruction set a = address high bits, b = address low bits, h = 0 - low byte, 1 - high byte, o = data out, i = data in, x = don?t care instruction tdi sequence tdo sequence notes 1a. chip erase 0100011_10000000 0110001_10000000 0110011_10000000 0110011_10000000 xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx 1b. poll for chip erase complete 0110011_10000000 xxxxx o x_xxxxxxxx (2) 2a. enter flash write 0100011_00010000 xxxxxxx_xxxxxxxx 2b. load address high byte 0000111_ aaaaaaaa xxxxxxx_xxxxxxxx (9) 2c. load address low byte 0000011_ bbbbbbbb xxxxxxx_xxxxxxxx 2d. load data low byte 0010011_ iiiiiiii xxxxxxx_xxxxxxxx 2e. load data high byte 0010111_ iiiiiiii xxxxxxx_xxxxxxxx 2f. latch data 0110111_00000000 1110111_00000000 0110111_00000000 xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx (1) 2g. write flash page 0110111_00000000 0110101_00000000 0110111_00000000 0110111_00000000 xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx (1) 2h. poll for page write complete 0110111_00000000 xxxxx o x_xxxxxxxx (2) 3a. enter flash read 0100011_00000010 xxxxxxx_xxxxxxxx 3b. load address high byte 0000111_ aaaaaaaa xxxxxxx_xxxxxxxx (9) 3c. load address low byte 0000011_ bbbbbbbb xxxxxxx_xxxxxxxx 3d. read data low and high byte 0110010_00000000 0110110_00000000 0110111_00000000 xxxxxxx_xxxxxxxx xxxxxxx_ oooooooo xxxxxxx_ oooooooo low byte high byte 4a. enter eeprom write 0100011_00010001 xxxxxxx_xxxxxxxx 4b. load address high byte 0000111_ aaaaaaaa xxxxxxx_xxxxxxxx (9) 4c. load address low byte 0000011_ bbbbbbbb xxxxxxx_xxxxxxxx 4d. load data byte 0010011_ iiiiiiii xxxxxxx_xxxxxxxx 4e. latch data 0110111_00000000 1110111_00000000 0110111_00000000 xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx (1) 4f. write eeprom page 0110011_00000000 0110001_00000000 0110011_00000000 0110011_00000000 xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx (1) 4g. poll for page write complete 0110011_00000000 xxxxx o x_xxxxxxxx (2) 5a. enter eeprom read 0100011_00000011 xxxxxxx_xxxxxxxx 5b. load address high byte 0000111_ aaaaaaaa xxxxxxx_xxxxxxxx (9) 290 2570n?avr?05/11 atmega325/3250/645/6450 5c. load address low byte 0000011_ bbbbbbbb xxxxxxx_xxxxxxxx 5d. read data byte 0110011_ bbbbbbbb 0110010_00000000 0110011_00000000 xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_ oooooooo 6a. enter fuse write 0100011_01000000 xxxxxxx_xxxxxxxx 6b. load data low byte (6) 0010011_ iiiiiiii xxxxxxx_xxxxxxxx (3) 6c. write fuse extended byte 0111011_00000000 0111001_00000000 0111011_00000000 0111011_00000000 xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx (1) 6d. poll for fuse write complete 0110111_00000000 xxxxx o x_xxxxxxxx (2) 6e. load data low byte (7) 0010011_ iiiiiiii xxxxxxx_xxxxxxxx (3) 6f. write fuse high byte 0110111_00000000 0110101_00000000 0110111_00000000 0110111_00000000 xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx (1) 6g. poll for fuse write complete 0110111_00000000 xxxxx o x_xxxxxxxx (2) 6h. load data low byte (7) 0010011_ iiiiiiii xxxxxxx_xxxxxxxx (3) 6i. write fuse low byte 0110011_00000000 0110001_00000000 0110011_00000000 0110011_00000000 xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx (1) 6j. poll for fuse write complete 0110011_00000000 xxxxx o x_xxxxxxxx (2) 7a. enter lock bit write 0100011_00100000 xxxxxxx_xxxxxxxx 7b. load data byte (9) 0010011_11 iiiiii xxxxxxx_xxxxxxxx (4) 7c. write lock bits 0110011_00000000 0110001_00000000 0110011_00000000 0110011_00000000 xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx (1) 7d. poll for lock bit write complete 0110011_00000000 xxxxx o x_xxxxxxxx (2) 8 a. enter fuse/lock bit read 0100011_00000100 xxxxxxx_xxxxxxxx 8 b. read extended fuse byte (6) 0111010_00000000 0111011_00000000 xxxxxxx_xxxxxxxx xxxxxxx_ oooooooo 8 c. read fuse high byte (7) 0111110_00000000 0111111_00000000 xxxxxxx_xxxxxxxx xxxxxxx_ oooooooo 8 d. read fuse low byte ( 8 ) 0110010_00000000 0110011_00000000 xxxxxxx_xxxxxxxx xxxxxxx_ oooooooo 8 e. read lock bits (9) 0110110_00000000 0110111_00000000 xxxxxxx_xxxxxxxx xxxxxxx_xx oooooo (5) table 27-16. jtag programming instruction set (continued) a = address high bits, b = address low bits, h = 0 - low byte, 1 - high byte, o = data out, i = data in, x = don?t care instruction tdi sequence tdo sequence notes 291 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. this command sequence is not required if the seven msb are correctly set by the previous command sequence (which is normally the case). 2. repeat until o = ?1?. 3. set bits to ?0? to program the corresponding fuse, ?1? to unprogram the fuse. 4. set bits to ?0? to program the corresponding lock bit, ?1? to leave the lock bit unchanged. 5. ?0? = programmed, ?1? = unprogrammed. 6. the bit mapping for fuses extended byte is listed in table 27-3 on page 266 7. the bit mapping for fuses high byte is listed in table 27-4 on page 267 8 . the bit mapping for fuses low byte is listed in table 27-5 on page 267 9. the bit mapping for lock bits byte is listed in table 27-1 on page 265 10. address bits exceeding pcmsb and eeamsb ( table 27-10 and table 27-11 ) are don?t care 11. all tdi and tdo sequences are represented by binary digits (0b...). 8 f. read fuses and lock bits 0111010_00000000 0111110_00000000 0110010_00000000 0110110_00000000 0110111_00000000 xxxxxxx_xxxxxxxx xxxxxxx_ oooooooo xxxxxxx_ oooooooo xxxxxxx_ oooooooo xxxxxxx_ oooooooo (5) fuse ext. byte fuse high byte fuse low byte lock bits 9a. enter signature byte read 0100011_00001000 xxxxxxx_xxxxxxxx 9b. load address byte 0000011_ bbbbbbbb xxxxxxx_xxxxxxxx 9c. read signature byte 0110010_00000000 0110011_00000000 xxxxxxx_xxxxxxxx xxxxxxx_ oooooooo 10a. enter calibration byte read 0100011_00001000 xxxxxxx_xxxxxxxx 10b. load address byte 0000011_ bbbbbbbb xxxxxxx_xxxxxxxx 10c. read calibration byte 0110110_00000000 0110111_00000000 xxxxxxx_xxxxxxxx xxxxxxx_ oooooooo 11a. load no operation command 0100011_00000000 0110011_00000000 xxxxxxx_xxxxxxxx xxxxxxx_xxxxxxxx table 27-16. jtag programming instruction set (continued) a = address high bits, b = address low bits, h = 0 - low byte, 1 - high byte, o = data out, i = data in, x = don?t care instruction tdi sequence tdo sequence notes 292 2570n?avr?05/11 atmega325/3250/645/6450 figure 27-15. state machine sequence for changing/reading the data word 27.8.11 flash data byte register the flash data byte register provides an ef ficient way to load the entire flash page buffer before executing page write, or to read out/verify the content of the flash. a state machine sets up the control signals to the flash and senses the strobe signals from the flash, thus only the data words need to be shifted in/out. the flash data byte register actually consists of the 8 -bit scan chain and a 8 -bit temporary reg- ister. during page load, the update-dr state copies the content of the scan chain over to the temporary register and initiates a write sequence that within 11 tck cycles loads the content of the temporary register into the flash page bu ffer. the avr automatically alternates between writing the low and the high byte for each new update-dr state, starting with the low byte for the first update-dr encountered after entering the prog_pageload command. the program counter is pre-incremented before writing the low byte, except for the first written byte. this ensures that the first data is written to the address set up by prog_commands, and loading the last location in the page buffer does not make the program counter increment into the next page. during page read, the content of the selected flash byte is captured into the flash data byte register during the capture-dr state. the avr automatically alternates between reading the low and the high byte for each new capture-dr state, starting with the low byte for the first cap- test-logic-reset run-test/idle shift-dr exit1-dr pause-dr exit2-dr update-dr select-ir scan capture-ir shift-ir exit1-ir pause-ir exit2-ir update-ir select-dr scan capture-dr 0 1 0 11 1 00 00 11 1 0 1 1 0 1 0 0 1 0 1 1 0 1 0 0 0 0 1 1 293 2570n?avr?05/11 atmega325/3250/645/6450 ture-dr encountered after entering the prog_pageread command. the program counter is post-incremented after reading each high byte, including the first read byte. this ensures that the first data is captured from the first ad dress set up by prog_commands, and reading the last location in the page makes the program counter increment into the next page. figure 27-16. flash data byte register the state machine controlling the flash data by te register is clocked by tck. during normal operation in which eight bits are shifted for eac h flash byte, the clock cycles needed to navigate through the tap controller automatically feeds the state machine for the flash data byte regis- ter with sufficient number of clock pulses to complete its operation transparently for the user. however, if too few bits are shifted between each update-dr state during page load, the tap controller should stay in the run-test/idle state for some tck cycles to ensure that there are at least 11 tck cycles between each update-dr state. 27.8.12 programming algorithm all references below of type ?1a?, ?1b?, and so on, refer to table 27-16 . 27.8.13 entering programming mode 1. enter jtag instruction avr_reset and shift 1 in the reset register. 2. enter instruction prog_enable and shift 0b1010_0011_0111_0000 in the program- ming enable register. 27.8.14 leaving programming mode 1. enter jtag instruction prog_commands. 2. disable all programming instructions by using no operation instruction 11a. 3. enter instruction prog_enable and shift 0b0000_0000_0000_0000 in the program- ming enable register. 4. enter jtag instruction avr_reset and shift 0 in the reset register. tdi tdo d a t a flash eeprom fuses lock bits strobes address state machine 294 2570n?avr?05/11 atmega325/3250/645/6450 27.8.15 performing chip erase 1. enter jtag instruction prog_commands. 2. start chip erase using pr ogramming instruction 1a. 3. poll for chip erase complete using programming instruction 1b, or wait for t wlrh_ce (refer to table 27-12 on page 279 ). 27.8.16 programming the flash before programming the flash a chip erase must be performed, see ?performing chip erase? on page 294. 1. enter jtag instruction prog_commands. 2. enable flash write using programming instruction 2a. 3. load address high byte using programming instruction 2b. 4. load address low byte using programming instruction 2c. 5. load data using programming instructions 2d, 2e and 2f. 6. repeat steps 4 and 5 for all instruction words in the page. 7. write the page using programming instruction 2g. 8 . poll for flash write complete using programming instruction 2h, or wait for t wlrh (refer to table 27-12 on page 279 ). 9. repeat steps 3 to 7 until all data have been programmed. a more efficient data transfer can be achieved using the prog_pageload instruction: 1. enter jtag instruction prog_commands. 2. enable flash write using programming instruction 2a. 3. load the page address using programming instructions 2b and 2c. pcword (refer to table 27-10 on page 270 ) is used to address within one page and must be written as 0. 4. enter jtag instruction prog_pageload. 5. load the entire page by shifting in all instruction words in the page byte-by-byte, starting with the lsb of the first instruction in the page and ending with the msb of the last instruction in the page. use update-dr to copy the contents of the flash data byte reg- ister into the flash page location and to auto-increment the program counter before each new word. 6. enter jtag instruction prog_commands. 7. write the page using programming instruction 2g. 8 . poll for flash write complete using programming instruction 2h, or wait for t wlrh (refer to table 27-12 on page 279 ). 9. repeat steps 3 to 8 until all data have been programmed. 27.8.17 reading the flash 1. enter jtag instruction prog_commands. 2. enable flash read using programming instruction 3a. 3. load address using programming instructions 3b and 3c. 4. read data using programming instruction 3d. 5. repeat steps 3 and 4 until all data have been read. a more efficient data transfer can be ac hieved using the prog_pageread instruction: 1. enter jtag instruction prog_commands. 2. enable flash read using programming instruction 3a. 295 2570n?avr?05/11 atmega325/3250/645/6450 3. load the page address using programming instructions 3b and 3c. pcword (refer to table 27-10 on page 270 ) is used to address within one page and must be written as 0. 4. enter jtag instruction prog_pageread. 5. read the entire page (or flash) by shifting out all instruction words in the page (or flash), starting with the lsb of the first instruction in the page (flash) and ending with the msb of the last instruction in the page (flash). the capture-dr state both captures the data from the flash, and also auto-increments the program counter after each word is read. note that capture-dr comes before the shift-dr state. hence, the first byte which is shifted out contains valid data. 6. enter jtag instruction prog_commands. 7. repeat steps 3 to 6 until all data have been read. 27.8.18 programming the eeprom before programming the eeprom a chip erase must be per formed, see ?performing chip erase? on page 294. 1. enter jtag instruction prog_commands. 2. enable eeprom write using programming instruction 4a. 3. load address high byte using programming instruction 4b. 4. load address low byte using programming instruction 4c. 5. load data using programming instructions 4d and 4e. 6. repeat steps 4 and 5 for all data bytes in the page. 7. write the data using programming instruction 4f. 8 . poll for eeprom write complete using pr ogramming instruction 4g, or wait for t wlrh (refer to table 27-12 on page 279 ). 9. repeat steps 3 to 8 until all data have been programmed. note that the prog_ pageload instruction can not be us ed when program ming the eeprom. 27.8.19 reading the eeprom 1. enter jtag instruction prog_commands. 2. enable eeprom read using programming instruction 5a. 3. load address using programming instructions 5b and 5c. 4. read data using programming instruction 5d. 5. repeat steps 3 and 4 until all data have been read. note that the prog_pageread instructio n can not be used when reading the eeprom. 27.8.20 programming the fuses 1. enter jtag instruction prog_commands. 2. enable fuse write using programming instruction 6a. 3. load data high byte using programming instru ctions 6b. a bit value of ?0? will program the corresponding fuse, a ?1? will unprogram the fuse. 4. write fuse high byte using programming instruction 6c. 5. poll for fuse write complete using prog ramming instruction 6d, or wait for t wlrh (refer to table 27-12 on page 279 ). 6. load data low byte using programming inst ructions 6e. a ?0? will pr ogram the fuse, a ?1? will unprogram the fuse. 7. write fuse low byte using programming instruction 6f. 296 2570n?avr?05/11 atmega325/3250/645/6450 8 . poll for fuse write complete using prog ramming instruction 6g, or wait for t wlrh (refer to table 27-12 on page 279 ). 27.8.21 programming the lock bits 1. enter jtag instruction prog_commands. 2. enable lock bit write using programming instruction 7a. 3. load data using prog ramming instructions 7b. a bit va lue of ?0? will program the corre- sponding lock bit, a ?1? will leave the lock bit unchanged. 4. write lock bits using programming instruction 7c. 5. poll for lock bit write complete using programming instruction 7d, or wait for t wlrh (refer to table 27-12 on page 279 ). 27.8.22 reading the fuses and lock bits 1. enter jtag instruction prog_commands. 2. enable fuse/lock bit read using programming instruction 8 a. 3. to read all fuses and lock bits, use programming instruction 8 e. to only read fuse high byte, use programming instruction 8 b. to only read fuse low byte, use programming instruction 8 c. to only read lock bits, use programming instruction 8 d. 27.8.23 reading the signature bytes 1. enter jtag instruction prog_commands. 2. enable signature byte read using programming instruction 9a. 3. load address 0x00 using programming instruction 9b. 4. read first signature byte using programming instruction 9c. 5. repeat steps 3 and 4 with address 0x01 and address 0x02 to read the second and third signature bytes, respectively. 27.8.24 reading the calibration byte 1. enter jtag instruction prog_commands. 2. enable calibration byte read using programming instruction 10a. 3. load address 0x00 using programming instruction 10b. read the calibration byte using programming instruction 10c. 297 2570n?avr?05/11 atmega325/3250/645/6450 28. electrical characteristics 28.1 absolute maximum ratings* 28.2 dc characteristics operating temperature.................................. -55 c to +125 c *notice: stresses beyond those listed under ?absolute maximum ratings? may cause permanent dam- age to the device. this is a stress rating only and functional operation of the device at these or other conditions beyond those indicated in the operational sections of th is specification is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. storage temperature ..................................... -65c to +150c voltage on any pin except reset with respect to ground ................................-0.5v to v cc +0.5v voltage on reset with respect to ground......-0.5v to +13.0v maximum operating voltage ............................................ 6.0v dc current per i/o pin ............................................... 40.0 ma dc current v cc and gnd pins................................ 200.0 ma table 28-1. t a = -40 c to 8 5 c, v cc = 1. 8 v to 5.5v (unless otherwise noted) symbol parameter condition min. typ. max. units v il input low voltage, except xtal1 pin v cc = 1. 8 v - 2.4v v cc = 2.4v - 5.5v -0.5 -0.5 0.2v cc (1) 0.3v cc (1) v v il1 input low voltage, xtal1 pin v cc = 1. 8 v - 5.5v -0.5 0.1v cc (1) v v ih input high voltage, except xtal1 and reset pins v cc = 1. 8 v - 2.4v v cc = 2.4v - 5.5v 0.7v cc (2) 0.6v cc (2) v cc + 0.5 v cc + 0.5 v v ih1 input high voltage, xtal1 pin v cc = 1. 8 v - 2.4v v cc = 2.4v - 5.5v 0. 8 v cc (2) 0.7v cc (2) v cc + 0.5 v cc + 0.5 v v ih2 input high voltage, reset pin v cc = 1. 8 v - 5.5v 0. 8 5v cc (2) v cc + 0.5 v v ol output low voltage (3) , port a, c, d, e, f, g, h, j i ol = 10ma, v cc = 5v i ol = 5ma, v cc = 3v 0.7 0.5 v v ol1 output low voltage (3) , port b i ol = 20ma, v cc = 5v i ol = 10ma, v cc = 3v 0.7 0.5 v v oh output high voltage (4) , port a, c, d, e, f, g, h, j i oh = -10ma, v cc = 5v i oh = -5ma, v cc = 3v 4.2 2.3 v v oh1 output high voltage (4) , port b i oh = -20ma, v cc = 5v i oh = -10ma, v cc = 3v 4.2 2.3 v i il input leakage current i/o pin v cc = 5.5v, pin low (absolute value) 1a i ih input leakage current i/o pin v cc = 5.5v, pin high (absolute value) 1a r rst reset pull-up resistor 20 100 k r pu i/o pin pull-up resistor 20 100 k 298 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. ?max? means the highest value where the pin is guaranteed to be read as low 2. ?min? means the lowest value where t he pin is guaranteed to be read as high 3. although each i/o port can sink more than the test conditions (20 ma at v cc = 5v, 10 ma at v cc = 3v for port b and 10 ma at v cc = 5v, 5 ma at v cc = 3v for all other ports) under steady state conditions (non-transient), the following must be observed: tqfp and qfn/mlf package: 1] the sum of all iol, for all ports, should not exceed 400 ma. 2] the sum of all iol, for ports a0 - a7, c4 - c7, g2 should not exceed 100 ma. 3] the sum of all iol, for ports b0 - b7, e0 - e7, g3 - g5 should not exceed 100 ma. 4] the sum of all iol, for ports d0 - d7, c0 - c3, g0 - g1 should not exceed 100 ma. 5] the sum of all iol, for ports f0 - f7, should not exceed 100 ma. if iol exceeds the test condition, vol may exceed the related sp ecification. pins are not guar anteed to sink current greater than the listed test condition. 4. although each i/o port can source more than the test conditions (20 ma at v cc = 5v, 10 ma at v cc = 3v for port b and 10ma at v cc = 5v, 5 ma at v cc = 3v for all other ports) under steady state conditions (non-transient), the following must be observed: tqfp and qfn/mlf package: 1] the sum of all iol, for all ports, should not exceed 400 ma. 2] the sum of all iol, for ports a0 - a7, c4 - c7, g2 should not exceed 100 ma. 3] the sum of all iol, for ports b0 - b7, e0 - e7, g3 - g5 should not exceed 100 ma. 4] the sum of all iol, for ports d0 - d7, c0 - c3, g0 - g1 should not exceed 100 ma. 5] the sum of all iol, for ports f0 - f7, should not exceed 100 ma. if ioh exceeds the test condition, voh ma y exceed the related specification. pins are not guaranteed to source current greater than the listed test condition. 5. typical values at 25 c. i cc power supply current active 1mhz, v cc = 2v 0.55 ma active 4mhz, v cc = 3v 2.5 ma active 8 mhz, v cc = 5v 9 ma idle 1mhz, v cc = 2v 0.2 ma idle 4mhz, v cc = 3v 0. 8 5ma idle 8 mhz, v cc = 5v 3 ma power-down mode (5) wdt enabled, v cc = 3v 7 15 a wdt disabled, v cc = 3v 0.25 5 a v acio analog comparator input offset voltage v cc = 5v v in = v cc /2 <10 40 mv i aclk analog comparator input leakage current v cc = 5v v in = v cc /2 -50 50 na t acid analog comparator propagation delay v cc = 2.7v v cc = 4.0v 750 500 ns table 28-1. t a = -40 c to 8 5 c, v cc = 1. 8 v to 5.5v (unless otherwise noted) (continued) symbol parameter condition min. typ. max. units 299 2570n?avr?05/11 atmega325/3250/645/6450 28.3 speed grades maximum frequency is dependent on v cc . as shown in figure 2 8 -1 on page 299 and figure 2 8 - 2 on page 299 , the maximum frequency vs. v cc curve is linear between 1. 8 v < v cc < 2.7v and between 2.7v < v cc < 4.5v. figure 28-1. maximum frequency vs. v cc (4 - 8 mhz). figure 28-2. maximum frequency vs. v cc ( 8 - 16 mhz). 8 mhz 4 mhz 1.8v 2.7v 5.5v safe operating area 16 mhz 8 mhz 2.7v 4.5v 5.5v safe operating area 300 2570n?avr?05/11 atmega325/3250/645/6450 28.4 clock characteristics 28.4.1 calibrated internal oscillator accuracy note: 1. voltage range for atmega325v/3250v/645v/6450v. 2. voltage range for atmel atmega325/3250/645/6450. 28.4.2 external clock drive waveforms figure 28-3. external clock drive waveforms 28.4.3 external clock drive table 28-2. calibration accuracy of internal rc oscillator frequency v cc temperature calibration accuracy factory calibration 8 .0 mhz 3v 25 c10% user calibration 7.3 - 8 .1 mhz 1. 8 v - 5.5v (1) 2.7v - 5.5v (2) -40 c - 8 5 c1% v il1 v ih1 table 28-3. external clock drive symbol parameter v cc =1.8-5.5v v cc =2.7-5.5v v cc =4.5-5.5v units min. max. min. max. min. max. 1/t clcl oscillator frequency 010 8 016mhz t clcl clock period 1000 125 62.5 ns t chcx high time 400 50 25 ns t clcx low time 400 50 25 ns t clch rise time 2.0 1.6 0.5 s t chcl fall time 2.0 1.6 0.5 s t clcl change in period from one clock cycle to the next 22 2% 301 2570n?avr?05/11 atmega325/3250/645/6450 28.5 system and reset characteristics notes: 1. the power-on reset will not work unless the supply voltage has been below v pot (falling) note: 1. v bot may be below nominal minimum operating voltage for some devices. for devices where this is the case, the device is tested down to v cc = v bot during the production test. this guarantees that a brown-out reset will occur before v cc drops to a voltage where correct operation of the microcontroller is no longer guaran teed. the test is performed using bodlevel = 10 for atmel atmega325/3250/645/6450 and bodlevel = 01 for atmel atmega325/3250/645/6450v. table 28-4. reset, brown-out and internal voltage reference characteristics symbol parameter condition min typ max units v pot (1) power-on reset threshold voltage (rising) t a = -40c to 8 5c 0.7 1.0 1.4 v power-on reset threshold voltage (falling) (1) t a = -40c to 8 5c 0.05 0.9 1.3 v v psr power-on slope rate 0.01 4.5 v/ms v rst reset pin threshold voltage v cc = 3v 0.2v cc 0. 8 5v cc v t rst minimum pulse width on reset pin v cc = 3v 8 00 ns v hyst brown-out detector hysteresis 50 mv t bod min pulse width on brown-out reset 2 s v bg bandgap reference voltage v cc = 2.7v, t a = 25 c1.0 1.1 1.2 v t bg bandgap reference start-up time v cc = 2.7v, t a = 25 c4070s i bg bandgap reference current consumption v cc = 2.7v, t a = 25 c15 a table 28-5. bodlevel fuse coding (1) bodlevel 2: 0 fuses min v bot typ v bot max v bot units 11 bod disabled 10 1.7 1. 8 2.0 v 01 2.5 2.7 2.9 00 4.1 4.3 4.5 302 2570n?avr?05/11 atmega325/3250/645/6450 28.6 spi timing characteristics see figure 2 8 -4 and figure 2 8 -5 for details. note: 1. in spi programming mode the minimum sck high/low period is: - 2 t clcl for f ck < 12 mhz - 3 t clcl for f ck > 12 mhz figure 28-4. spi interface timing requirements (master mode) table 28-6. spi timing parameters description mode min typ max 1 sck period master see table 19-5 ns 2 sck high/low master 50% duty cycle 3 rise/fall time master 3.6 4 setup master 10 5holdmaster 10 6 out to sck master 0.5 ? t sck 7 sck to out master 10 8 sck to out high master 10 9ss low to out slave 15 10 sck period slave 4 ? t ck 11 sck high/low (1) slave 2 ? t ck 12 rise/fall time slave 1.6 s 13 setup slave 10 ns 14 hold slave t ck 15 sck to out slave 15 16 sck to ss high slave 20 17 ss high to tri-state slave 10 1 8 ss low to sck slave 20 ? t ck mo si (data output) sck (cpol = 1) mi so (data input) sck (cpol = 0) ss msb lsb lsb msb ... ... 61 22 3 45 8 7 303 2570n?avr?05/11 atmega325/3250/645/6450 figure 28-5. spi interface timing requirements (slave mode) mi so (data output) sck (cpol = 1) mo si (data input) sck (cpol = 0) ss msb lsb lsb msb ... ... 10 11 11 12 13 14 17 15 9 x 16 304 2570n?avr?05/11 atmega325/3250/645/6450 28.7 adc table 28-7. adc characteristics symbol parameter condition min typ max units resolution single ended conversion 10 bits differential conversion 8 bits absolute accuracy (including inl, dnl, quantization error, gain and offset error) single ended conversion v ref = 4v, v cc = 4v, adc clock = 200khz 22.5lsb single ended conversion v ref = 4v, v cc = 4v, adc clock = 1mhz 4.5 lsb single ended conversion v ref = 4v, v cc = 4v, adc clock = 200khz noise reduction mode 2lsb single ended conversion v ref = 4v, v cc = 4v, adc clock = 1 mhz noise reduction mode 4.5 lsb integral non-linearity (inl) single ended conversion v ref = 4v, v cc = 4v, adc clock = 200khz 0.5 lsb differential non-linearity (dnl) single ended conversion v ref = 4v, v cc = 4v, adc clock = 200khz 0.25 lsb gain error single ended conversion v ref = 4v, v cc = 4v, adc clock = 200khz 2lsb offset error single ended conversion v ref = 4v, v cc = 4v, adc clock = 200khz 2lsb conversion time free running conversion 13 260 s clock frequency single ended conversion 50 1000 khz avcc analog supply voltage v cc - 0.3 v cc + 0.3 v v ref reference voltage single ended conversion 1.0 avcc v differential conversion 1.0 avcc - 0.5 v v in pin input voltage single ended channels gnd v ref v differential channels gnd avcc v input range single ended channels gnd v ref v differential channels (1) -0. 8 5v ref v ref v input bandwidth single ended channels 3 8 ,5 khz differential channels 4 khz 305 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. voltage difference between channels v int internal voltage reference 1.0 1.1 1.2 v r ref reference input resistance 32 k r ain analog input resistance 100 m table 28-7. adc characteristics symbol parameter condition min typ max units 306 2570n?avr?05/11 atmega325/3250/645/6450 29. typical characteristics the following charts show typical behavior. t hese figures are not tested during manufacturing. all current consumption measurements are performed with all i/o pins configured as inputs and with internal pull-ups enabled. a sine wave generator with rail-to-rail output is used as clock source. all active- and idle current consumption measurements are done with all bits in the prr register set and thus, the corresponding i/o modules are turned off. also the analog comparator is dis- abled during these measurements. see ?power reduction register? on page 37 for details. the power consumption in power-down mode is independent of clock selection. the current consumption is a function of several factors such as: operating voltage, operating frequency, loading of i/o pins, switching rate of i/o pins, code executed and ambient tempera- ture. the dominating factors are operating voltage and frequency. the current drawn from capacitive loaded pins may be estimated (for one pin) as c l * v cc *f where c l = load capacitance, v cc = operating voltage and f = average switching frequency of i/o pin. the parts are characterized at frequencies higher than test limits. parts are not guaranteed to function properly at frequencies higher than the ordering code indicates. the difference between current consumption in power-down mode with watchdog timer enabled and power-down mode with watchdog timer disabled represents the differential cur- rent drawn by the watchdog timer. 29.1 active supply current figure 29-1. active supply current vs. frequency (0.1 - 1.0mhz) 5.5 v 5.0 v 4.5 v 4.0 v 3.3 v 2.7 v 1.8 v 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0. 9 1 frequency (mhz) i cc (m a) 307 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-2. active supply current vs . frequency (1 - 16mhz)) figure 29-3. active supply current vs. v cc (internal rc oscillator, 8 mhz) 5.5 v 5.0 v 4.5 v 4.0 v 3.3 v 2.7 v 1.8 v 0 2 4 6 8 10 12 14 16 0246810121416 frequency (mhz) i cc (ma) 0 2 4 6 8 10 12 14 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ma) 85 c 25 c -40 c 308 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-4. active supply current vs. v cc (internal rc o scillator, ckdiv 8 programmed, 1mhz) figure 29-5. active supply current vs. v cc (32khz external oscillator) 0 0.5 1 1.5 2 2.5 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ma) 85 c 25 c -40 c 85 c 25 c -40 c 0 10 20 30 40 50 60 70 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (u a) 309 2570n?avr?05/11 atmega325/3250/645/6450 29.2 idle supply current figure 29-6. idle supply current vs. frequency (0.1 - 1.0 mhz) figure 29-7. idle supply current vs. frequency (1 - 16mhz) 5.5 v 5.0 v 4.5 v 4.0 v 3.3 v 2.7 v 1.8 v 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0. 9 1 frequency (mhz) i cc (ma) 5.5 v 5.0 v 4.5 v 4.0 v 3.3 v 2.7 v 0 1 2 3 4 5 6 0246810121416 frequency (mhz) i cc (ma) 1.8 v 310 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-8. idle supply current vs. v cc (internal rc oscillator, 8 mhz) figure 29-9. idle supply current vs. v cc (internal rc oscillator, ckdiv 8 programmed, 1mhz) 0 1 2 3 4 5 6 7 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ma) 85 c 25 c -40 c 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0. 9 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ma) 85 c 25 c -40 c 311 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-10. idle supply current vs. v cc (32khz external oscillator) 29.3 supply current of i/o modules the tables and formulas below can be used to calculate the additional current consumption for the different i/o modules in active and idle mode. the enabling or disabling of the i/o modules are controlled by the power reduction register. see ?prr ? power reduction register? on page 40 for details. it is possible to calculate the typical current consumption based on the numbers from table 29-2 for other v cc and frequency settings than listed in table 29-1 . 85 c 25 c -40 c 0 5 10 15 20 25 30 35 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ua) table 29-1. additional current consumption for the different i/o modules (absolute values) prr bit typical numbers v cc = 2v, f = 1mhz v cc = 3v, f = 4mhz v cc = 5v, f = 8mhz pradc 17a 116a 562a prusart0 9a 59a 24 8 a prspi 10a 62a 257a prtim1 5a 33a 135a table 29-2. additional current consumption (percentage) in active and idle mode prr bit additional current consumption compared to active with external clock (see figure 29-1 and figure 29-2 ) additional current consumption compared to idle with external clock (see figure 29-6 and figure 29-7 ) pradc 5.4% 16. 8 % prusart0 2.7% 8 .5% prspi 2.9% 9.0% prtim1 1.5% 4. 8 % 312 2570n?avr?05/11 atmega325/3250/645/6450 29.3.0.1 example calculate the expected current consumption in idle mode with usart0, timer1, and spi enabled at v cc = 3.0v and f = 1mhz. table 29-2 shows that we need to add 8 .5% for the usart0, 9% for the spi, and 4. 8 % for the timer1 module. from figure 29-6 , we find that the idle current consumption is ~0.16ma at v cc = 3.0v and f = 1mhz. the total current consump- tion in idle mode with usart0, timer1, and spi enabled, gives: 29.4 power-down supply current figure 29-11. power-down supply current vs. v cc (watchdog timer disabled) figure 29-12. power-down supply current vs. v cc (watchdog timer enabled) i cc total 0.16 ma 10.0 8 50.090.04 8 +++ () ? 0.20 ma ? 85 c 25 c -40 c 0 0.5 1 1.5 2 2.5 3 3.5 4 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ua) 85 c 25 c -40 c 0 2 4 6 8 10 12 14 16 18 20 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ua) 313 2570n?avr?05/11 atmega325/3250/645/6450 29.5 power-save supply current figure 29-13. power-save supply current vs. v cc (watchdog timer disabled) 29.6 standby supply current figure 29-14. standby supply current vs. v cc (low power cr ystal oscillator) 0 5 10 15 20 25 30 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ua) 85 c 25 c 6mhz xtal 6mhz res. 4mhz xtal 4mhz res. 455khz res. 32khz xtal 2mhz xtal 2mhz res. 1mhz res. 0 20 40 60 80 100 120 140 160 180 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc ( v ) i cc ( u a) 314 2570n?avr?05/11 atmega325/3250/645/6450 29.7 pin pull-up figure 29-15. i/o pin pull-up resistor current vs. input voltage (v cc = 5v) figure 29-16. i/o pin pull-up resistor current vs. input voltage (v cc = 2.7v) 0 20 40 60 80 100 120 140 160 012345 v io (v) i io (ua) 85 c 25 c -40 c 0 10 20 30 40 50 60 70 80 9 0 0 0.5 1 1.5 2 2.5 3 v io (v) i io (ua) 85 c 25 c -40 c 315 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-17. i/o pin pull-up resistor current vs. input voltage (v cc = 1. 8 v) figure 29-18. reset pull-up resistor curr ent vs. reset pin voltage (v cc = 5v) 0 10 20 30 40 50 60 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 v op (v) i op (ua) 85 c 25 c -40 c 0 20 40 60 80 100 120 012345 v reset (v) i reset (ua) -40 c 25 c 85 c 316 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-19. reset pull-up resistor curr ent vs. reset pin voltage (v cc = 2.7v) figure 29-20. reset pull-up resistor curr ent vs. reset pin voltage (v cc = 1. 8 v) 0 10 20 30 40 50 60 70 0 0.5 1 1.5 2 2.5 3 v reset (v) i reset (ua) -40 c 25 c 85 c 0 5 10 15 20 25 30 35 40 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 v reset (v) i reset (ua) -40 c 25 c 85 c 317 2570n?avr?05/11 atmega325/3250/645/6450 29.8 pin driver strength figure 29-21. i/o pin source current vs. output voltag e, ports a, c, d, e, f, g, h, j (v cc =5v) figure 29-22. i/o pin source current vs. output voltage, ports a, c, d, e, f, g, h, j (v cc =2.7v) 0 10 20 30 40 50 60 70 0123456 v oh ( v ) i oh (ma) 85 c 25 c -40 c 0 5 10 15 20 25 0 0.5 1 1.5 2 2.5 3 v oh (v) i oh (ma) 85 c 25 c -40 c 318 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-23. i/o pin source current vs. output voltage, ports a, c, d, e, f, g, h, j (v cc =1. 8 v) figure 29-24. i/o pin source current vs. output voltage, port b (v cc = 5v) 0 1 2 3 4 5 6 7 8 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 v oh (v) i oh (ma) 85 c 25 c -40 c 0 10 20 30 40 50 60 70 80 01234 v oh (v) i oh (ma) 85 c 25 c -40 c 319 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-25. i/o pin source current vs. output voltage, port b (v cc = 2.7v) figure 29-26. i/o pin source current vs. output voltage, port b (v cc = 1. 8 v) 0 5 10 15 20 25 30 35 0 0.5 1 1.5 2 2.5 3 v oh (v) i oh (ma) 85 c 25 c -40 c 0 1 2 3 4 5 6 7 8 9 10 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 v oh (v) i oh (ma) 85 c 25 c -40 c 320 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-27. i/o pin sink current vs. output voltage, ports a, c, d, e, f, g, h, j (v cc = 5v) figure 29-28. i/o pin sink current vs. output voltage, ports a, c, d, e, f, g, h, j (v cc = 2.7v) 0 5 10 15 20 25 30 35 40 45 50 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 v ol (v) i ol (ma) 85 c 25 c -40 c 0 2 4 6 8 10 12 14 16 18 20 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 v ol (v) i ol (ma) 85 c 25 c -40 c 321 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-29. i/o pin sink current vs. output voltage, ports a, c, d, e, f, g, h, j (v cc = 1. 8 v) figure 29-30. i/o pin sink current vs. output voltage, port b (v cc = 5v) 0 1 2 3 4 5 6 7 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 v ol (v) i ol (ma) 85 c 25 c -40 c 0 10 20 30 40 50 60 70 80 9 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 v ol (v) i ol (ma) 85 c 25 c -40 c 322 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-31. i/o pin sink current vs. output voltage, port b (v cc = 2.7v) figure 29-32. i/o pin sink current vs. output voltage, port b (v cc = 1. 8 v) 0 5 10 15 20 25 30 35 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 v ol (v) i ol (ma) 85 c 25 c -40 c 0 2 4 6 8 10 12 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 v ol (v) i ol (ma) 85 c 25 c -40 c 323 2570n?avr?05/11 atmega325/3250/645/6450 29.9 pin thresholds and hysteresis figure 29-33. i/o pin input threshold voltage vs. v cc (v ih , i/o pin read as ?1?) figure 29-34. i/o pin input threshold voltage vs. v cc (v il , i/o pin read as ?0?) 0 0.5 1 1.5 2 2.5 3 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) threshold (v) 85 c 25 c -40 c 0 0.5 1 1.5 2 2.5 3 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) threshold (v) 85 c 25 c -40 c 324 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-35. i/o pin input hysteresis vs. v cc figure 29-36. reset input threshold voltage vs. v cc (v ih ,reset pin read as ?1?) 0 0.1 0.2 0.3 0.4 0.5 0.6 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) 85 c 25 c -40 c input hysteresis (v) 0 0.5 1 1.5 2 2.5 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) threshold (v) 85 c 25 c -40 c 325 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-37. reset input threshold voltage vs. v cc (v il ,reset pin read as ?0?) figure 29-38. reset input pin hysteresis vs. v cc 0 0.5 1 1.5 2 2.5 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) threshold (v) 85 c 25 c -40 c 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) 85 c 25 c -40 c input hysteresis (v) 326 2570n?avr?05/11 atmega325/3250/645/6450 29.10 bod thresholds and anal og comparator offset figure 29-39. bod thresholds vs. temperature (bod level is 4.3v) figure 29-40. bod thresholds vs. temperature (bod level is 2.7v) rising v cc falling v cc 4 4.1 4.2 4.3 4.4 4.5 4.6 -60 -40 -20 0 20 40 60 80 100 temperature (c) threshold (v) rising v cc falling v cc 2.4 2.5 2.6 2.7 2.8 2. 9 3 -60 -40 -20 0 20 40 60 80 100 temperature (c) threshol d ( v) 327 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-41. bod thresholds vs. temperature (bod level is 1. 8 v) figure 29-42. bandgap voltage vs. v cc 1.7 1.75 1.8 1.85 1. 9 1. 9 5 -60 -40 -20 0 20 40 60 80 100 temperature (c) threshold (v) rising v cc falling v cc 85c 25c -40c 1.068 1.06 9 1.07 1.071 1.072 1.073 1.074 1.075 1.076 1.5 2 2.5 3 3.5 4 4.5 5 v cc (v) bandgap voltage (v) 328 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-43. analog comparator offset voltage vs. common mode voltage (v cc = 5v) figure 29-44. analog comparator offset voltage vs. common mode voltage (v cc =2.7v) 85c 25c -40c 0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 common mode voltage (v) comparator offset voltage (v) 85c 25c -40c 0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0 0.5 1 1.5 2 2.5 3 common mode voltage (v) comparator offset voltage (v) 329 2570n?avr?05/11 atmega325/3250/645/6450 29.11 internal oscillator speed figure 29-45. watchdog oscillato r frequency vs. v cc figure 29-46. calibrated 8 mhz rc oscillator freq uency vs. temperature 85 c 25 c -40 c 1000 1050 1100 1150 1200 1250 1300 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) f rc (khz) 5.5 v 4.5 v 3.3 v 2.7 v 1.8 v 7.2 7.4 7.6 7.8 8 8.2 8.4 8.6 -60 -40 -20 0 20 40 60 80 100 temperature (c) f rc (m hz) 330 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-47. calibrated 8 mhz rc oscillator frequency vs. v cc figure 29-48. calibrated 8 mhz rc oscillator frequen cy vs. osccal value cc 85 c 25 c -40 c 7.2 7.4 7.6 7.8 8 8.2 8.4 8.6 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) f rc (mhz) 85 c 25 c -40 c 4 6 8 10 12 14 16 01632486480 9 6 112 128 144 160 176 1 9 2 208 224 240 256 osccal value f rc (m hz) 331 2570n?avr?05/11 atmega325/3250/645/6450 29.12 current consumption of peripheral units figure 29-49. brownout detector current vs. v cc figure 29-50. adc current vs. v cc (aref = avcc) 85 c 25 c -40 c 0 5 10 15 20 25 30 35 40 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc ( v ) i cc ( u a) 0 50 100 150 200 250 300 350 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ua) 85 c 25 c -40 c 332 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-51. aref external reference current vs. v cc figure 29-52. 32khz tosc current vs. v cc (watchdog timer disabled) 0 20 40 60 80 100 120 140 160 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i aref (ua) 85 c 25 c -40 c 0 5 10 15 20 25 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ua) 85 c 25 c 333 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-53. watchdog timer current vs. v cc figure 29-54. analog comparator current vs. v cc 0 2 4 6 8 10 12 14 16 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ua) 85 c 25 c -40 c 0 20 40 60 80 100 120 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ua) 85 c 25 c -40 c 334 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-55. programming current vs. v cc 29.13 current consumption in reset and reset pulsewidth figure 29-56. reset supply current vs. v cc (0.1 - 1.0mhz, excluding current through the reset pull-up) 85 c 25 c -40 c 0 2 4 6 8 10 12 14 16 18 20 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) i cc (ma) 5.5 v 5.0 v 4.5 v 4.0 v 3.3 v 2.7 v 1.8 v 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0. 9 1 frequency (mhz) i cc (ma) 335 2570n?avr?05/11 atmega325/3250/645/6450 figure 29-57. reset supply current vs. v cc (1 - 16mhz, excluding current through the reset pull-up) figure 29-58. reset pulse width vs. v cc 5.5 v 5.0 v 4.5 v 4.0 v 3.3 v 2.7 v 1.8 v 0 0.5 1 1.5 2 2.5 3 0246810121416 frequency (mhz) i cc (ma) 0 500 1000 1500 2000 2500 1.5 2 2.5 3 3.5 4 4.5 5 5.5 v cc (v) pulsewidth (ns) 85 c 25 c -40 c 336 2570n?avr?05/11 atmega325/3250/645/6450 30. register summary note: registers with bold type only available in atmega3250/6450. address name bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 page (0xff) reserved - - - - - - - - (0xfe) reserved - - - - - - - - (0xfd) reserved - - - - - - - - (0xfc) reserved - - - - - - - - (0xfb) reserved - - - - - - - - (0xfa) reserved - - - - - - - - (0xf9) reserved - - - - - - - - (0xf 8 ) reserved - - - - - - - - (0xf7) reserved - - - - - - - - (0xf6) reserved - - - - - - - - (0xf5) reserved - - - - - - - - (0xf4) reserved - - - - - - - - (0xf3) reserved - - - - - - - - (0xf2) reserved - - - - - - - - (0xf1) reserved - - - - - - - - (0xf0) reserved - - - - - - - - (0xef) reserved - - - - - - - - (0xee) reserved - - - - - - - - (0xed) reserved - - - - - - - - (0xec) reserved - - - - - - - - (0xeb) reserved - - - - - - - - (0xea) reserved - - - - - - - - (0xe9) reserved - - - - - - - - (0xe 8 ) reserved - - - - - - - - (0xe7) reserved - - - - - - - - (0xe6) reserved - - - - - - - - (0xe5) reserved - - - - - - - - (0xe4) reserved - - - - - - - - (0xe3) reserved - - - - - - - - (0xe2) reserved - - - - - - - - (0xe1) reserved - - - - - - - - (0xe0) reserved - - - - - - - - (0xdf) reserved - - - - - - - - (0xde) reserved - - - - - - - - (0xdd) portj - portj6 portj5 portj4 portj3 portj2 portj1 portj0 8 4 (0xdc) ddrj - ddj6 ddj5 ddj4 ddj3 ddj2 ddj1 ddj0 8 4 (0xdb) pinj - pinj6 pinj5 pinj4 pinj3 pinj2 pinj1 pinj0 8 4 (0xda) porth porth7 porth6 porth5 porth4 porth3 porth2 porth1 porth0 8 4 (0xd9) ddrh ddh7 ddh6 ddh5 ddh4 ddh3 ddh2 ddh1 ddh0 8 4 (0xd 8 ) pinh pinh7 pinh6 pinh5 pinh4 pinh3 pinh2 pinh1 pinh0 8 4 (0xd7) reserved - - - - - - - - (0xd6) reserved - - - - - - - - (0xd5) reserved - - - - - - - - (0xd4) reserved - - - - - - - - (0xd3) reserved - - - - - - - - (0xd2) reserved - - - - - - - - (0xd1) reserved - - - - - - - - (0xd0) reserved - - - - - - - - (0xcf) reserved - - - - - - - - (0xce) reserved - - - - - - - - (0xcd) reserved - - - - - - - - (0xcc) reserved - - - - - - - - (0xcb) reserved - - - - - - - - (0xca) reserved - - - - - - - - (0xc9) reserved - - - - - - - - (0xc 8 ) reserved - - - - - - - - (0xc7) reserved - - - - - - - - (0xc6) udr0 usart0 data register 179 (0xc5) ubrr0h usart0 baud rate register high 1 8 4 (0xc4) ubrr0l usart0 baud rate register low 1 8 4 337 2570n?avr?05/11 atmega325/3250/645/6450 (0xc3) reserved - - - - - - - - (0xc2) ucsr0c - umsel0 upm01 upm00 usbs0 ucsz01 ucsz00 ucpol0 1 8 2 (0xc1) ucsr0b rxcie0 txcie0 udrie0 rxen0 txen0 ucsz02 rxb 8 0txb 8 01 8 1 (0xc0) ucsr0a rxc0 txc0 udre0 fe0 dor0 upe0 u2x0 mpcm0 1 8 0 (0xbf) reserved - - - - - - - - (0xbe) reserved - - - - - - - - (0xbd) reserved - - - - - - - - (0xbc) reserved - - - - - - - - (0xbb) reserved - - - - - - - - (0xba) usidr usi data register 192 (0xb9) usisr usisif usioif usipf usidc us icnt3 usicnt2 usicnt1 usicnt0 193 (0xb 8 ) usicr usisie usioie usiwm1 usiwm0 usics1 usics0 usiclk usitc 194 (0xb7) reserved - - - - - - - - (0xb6) assr - - - exclk as2 tcn2ub ocr2ub tcr2ub 145 (0xb5) reserved - - - - - - - - (0xb4) reserved - - - - - - - - (0xb3) ocr2a timer/counter 2 output compare register a 145 (0xb2) tcnt2 timer/counter2 145 (0xb1) reserved - - - - - - - - (0xb0) tccr2a foc2a wgm20 com2a1 com2a0 wgm21 cs22 cs21 cs20 143 (0xaf) reserved - - - - - - - - (0xae) reserved - - - - - - - - (0xad) reserved - - - - - - - - (0xac) reserved - - - - - - - - (0xab) reserved - - - - - - - - (0xaa) reserved - - - - - - - - (0xa9) reserved - - - - - - - - (0xa 8 ) reserved - - - - - - - - (0xa7) reserved - - - - - - - - (0xa6) reserved - - - - - - - - (0xa5) reserved - - - - - - - - (0xa4) reserved - - - - - - - - (0xa3) reserved - - - - - - - - (0xa2) reserved - - - - - - - - (0xa1) reserved - - - - - - - - (0xa0) reserved - - - - - - - - (0x9f) reserved - - - - - - - - (0x9e) reserved - - - - - - - - (0x9d) reserved - - - - - - - - (0x9c) reserved - - - - - - - - (0x9b) reserved - - - - - - - - (0x9a) reserved - - - - - - - - (0x99) reserved - - - - - - - - (0x9 8 ) reserved - - - - - - - - (0x97) reserved - - - - - - - - (0x96) reserved - - - - - - - - (0x95) reserved - - - - - - - - (0x94) reserved - - - - - - - - (0x93) reserved - - - - - - - - (0x92) reserved - - - - - - - - (0x91) reserved - - - - - - - - (0x90) reserved - - - - - - - - (0x 8 f) reserved - - - - - - - - (0x 8 e) reserved - - - - - - - - (0x 8 d) reserved - - - - - - - - (0x 8 c) reserved - - - - - - - - (0x 8 b) ocr1bh timer/counter1 output compare register b high 127 (0x 8 a) ocr1bl timer/counter1 output compare register b low 127 (0x 8 9) ocr1ah timer/counter1 output compare register a high 127 (0x 88 ) ocr1al timer/counter1 output compare register a low 127 (0x 8 7) icr1h timer/counter1 input capture register high 127 (0x 8 6) icr1l timer/counter1 input capture register low 127 (0x 8 5) tcnt1h timer/counter1 high 127 address name bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 page 338 2570n?avr?05/11 atmega325/3250/645/6450 (0x 8 4) tcnt1l timer/counter1 low 127 (0x 8 3) reserved - - - - - - - - (0x 8 2) tccr1c foc1a foc1b - - - - - -126 (0x 8 1) tccr1b icnc1 ices1 - wgm13wgm12cs12cs11cs10 125 (0x 8 0) tccr1a com1a1 com1a0 com1b1 com1b0 - -wgm11wgm10123 (0x7f) didr1 - - - - - - ain1d ain0d 200 (0x7e) didr0 adc7d adc6d adc5d adc4d adc3d adc2d adc1d adc0d 217 (0x7d) reserved - - - - - - - - (0x7c) admux refs1 refs0 adlar mux4 mux3 mux2 mux1 mux0 213 (0x7b) adcsrb -acme - - - adts2 adts1 adts0 19 8 /217 (0x7a) adcsra aden adsc adate adi f adie adps2 adps1 adps0 215 (0x79) adch adc data register high 216 (0x7 8 ) adcl adc data register low 216 (0x77) reserved - - - - - - - - (0x76) reserved - - - - - - - - (0x75) reserved - - - - - - - - (0x74) reserved - - - - - - - - (0x73) pcmsk3 - pcint30 pcint29 pcint28 pcint27 pcint26 pcint25 pcint24 5 8 (0x72) reserved - - - - - - - - (0x71) reserved - - - - - - - - (0x70) timsk2 - - - - - - ocie2a toie2 146 (0x6f) timsk1 - -icie1 - - ocie1b ocie1a toie1 12 8 (0x6e) timsk0 - - - - - - ocie0a toie0 99 (0x6d) pcmsk2 pcint23 pcint22 pcint21 pcint20 pcint19 pcint18 pcint17 pcint16 5 8 (0x6c) pcmsk1 pcint15 pcint14 pcint13 pcint12 pcint11 pcint10 pcint9 pcint 8 59 (0x6b) pcmsk0 pcint7 pcint6 pcint5 pcint4 pcint3 pcint2 pcint1 pcint0 59 (0x6a) reserved - - - - - - - - (0x69) eicra - - - - - -isc01isc0056 (0x6 8 ) reserved - - - - - - - - (0x67) reserved - - - - - - - - (0x66) osccal oscillator calibration register [cal7..0] 32 (0x65) reserved - - - - - - - - (0x64) prr - - - - prtim1 prspi psusart0 pradc 40 (0x63) reserved - - - - - - - - (0x62) reserved - - - - - - - - (0x61) clkpr clkpce - - - clkps3 clkps2 clkps1 clkps0 32 (0x60) wdtcr - - - wdce wde wdp2 wdp1 wdp0 47 0x3f (0x5f) sreg i t h s v n z c 12 0x3e (0x5e) sph stack pointer high 14 0x3d (0x5d) spl stack pointer low 14 0x3c (0x5c) reserved - - - - - - - - 0x3b (0x5b) reserved - - - - - - - - 0x3a (0x5a) reserved - - - - - - - - 0x39 (0x59) reserved - - - - - - - - 0x3 8 (0x5 8 ) reserved - - - - - - - - 0x37 (0x57) spmcsr spmie rwwsb - rwwsre blbset pgwrt pgers spmen 263 0x36 (0x56) reserved 0x35 (0x55) mcucr jtd - -pud --ivselivce53/ 8 1/227 0x34 (0x54) mcusr - - - jtrf wdrf borf extrf porf 47 0x33 (0x53) smcr - - - - sm2 sm1 sm0 se 35 0x32 (0x52) reserved - - - - - - - - 0x31 (0x51) ocdr idrd/ocdr7 ocdr6 ocdr5 o cdr4 ocdr3 ocdr2 ocdr1 ocdr0 223 0x30 (0x50) acsr acd acbg aco aci acie acic acis1 acis0 19 8 0x2f (0x4f) reserved - - - - - - - - 0x2e (0x4e) spdr spi data register 156 0x2d (0x4d) spsr spif wcol - - - - - spi2x 156 0x2c (0x4c) spcr spie spe dord mstr cpol cpha spr1 spr0 154 0x2b (0x4b) gpior2 general purpose i/o register 25 0x2a (0x4a) gpior1 general purpose i/o register 25 0x29 (0x49) reserved - - - - - - - - 0x2 8 (0x4 8 ) reserved - - - - - - - - 0x27 (0x47) ocr0a timer/counter0 output compare a 9 8 0x26 (0x46) tcnt0 timer/counter0 9 8 address name bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 page 339 2570n?avr?05/11 atmega325/3250/645/6450 note: 1. for compatibility with future devices, reserved bits s hould be written to zero if accessed. reserved i/o memory addresse s should never be written. 2. i/o registers within the address range 0x00 - 0x1f are directly bit-accessible using the sbi and cbi instructions. in these registers, the value of single bits can be ch ecked by using the sbis and sbic instructions. 3. some of the status flags are cleared by writing a logical o ne to them. note that, unlike most other avrs, the cbi and sbi instructions will only operate on the specif ied bit, and can therefore be used on regi sters containing such status flags. the cbi and sbi instructions work wit h registers 0x00 to 0x1f only. 4. when using the i/o specific commands in and out, the i/o addresses 0x00 - 0x3f must be used. when addressing i/o registers as data space using ld and st instructi ons, 0x20 must be added to these addresses. the atmel atmega325/3250/645/6450 is a complex microcontroller with mo re peripheral units than can be supported within the 64 location reserved in opcode for the in and out instructions . for the extended i/o space from 0x60 - 0xff in sram, only the st/sts/std and ld/lds/ldd instructions can be used. 0x25 (0x45) reserved - - - - - - - - 0x24 (0x44) tccr0a foc0a wgm00 com0a1 com0a0 wgm01 cs02 cs01 cs00 96 0x23 (0x43) gtccr tsm - - - - - psr2 psr10 101/147 0x22 (0x42) eearh - - - - - eeprom address register high 22 0x21 (0x41) eearl eeprom address register low 22 0x20 (0x40) eedr eeprom data register 22 0x1f (0x3f) eecr - - - - eerie eemwe eewe eere 22 0x1e (0x3e) gpior0 general purpose i/o register 25 0x1d (0x3d) eimsk pcie3 pcie2 pcie1 pcie0 - - -int057 0x1c (0x3c) eifr pcif3 pcif2 pcif1 pcif0 - - - intf0 57 0x1b (0x3b) reserved - - - - - - - - 0x1a (0x3a) reserved - - - - - - - - 0x19 (0x39) reserved - - - - - - - - 0x1 8 (0x3 8 ) reserved - - - - - - - - 0x17 (0x37) tifr2 - - - - - -ocf2atov2147 0x16 (0x36) tifr1 - -icf1 - -ocf1bocf1atov112 8 0x15 (0x35) tifr0 - - - - - -ocf0atov099 0x14 (0x34) portg - - - portg4 portg3 portg2 portg1 portg0 8 3 0x13 (0x33) ddrg - - - ddg4 ddg3 ddg2 ddg1 ddg0 8 4 0x12 (0x32) ping - - ping5 ping4 ping3 ping2 ping1 ping0 8 4 0x11 (0x31) portf portf7 portf6 portf5 portf4 portf3 portf2 portf1 portf0 8 3 0x10 (0x30) ddrf ddf7 ddf6 ddf5 ddf4 ddf3 ddf2 ddf1 ddf0 8 3 0x0f (0x2f) pinf pinf7 pinf6 pinf5 pinf4 pinf3 pinf2 pinf1 pinf0 8 3 0x0e (0x2e) porte porte7 porte6 porte5 porte4 porte3 porte2 porte1 porte0 8 3 0x0d (0x2d) ddre dde7 dde6 dde5 dde4 dde3 dde2 dde1 dde0 8 3 0x0c (0x2c) pine pine7 pine6 pine5 pine4 pine3 pine2 pine1 pine0 8 3 0x0b (0x2b) portd portd7 portd6 portd5 portd4 portd3 portd2 portd1 portd0 8 2 0x0a (0x2a) ddrd ddd7 ddd6 ddd5 ddd4 ddd3 ddd2 ddd1 ddd0 8 2 0x09 (0x29) pind pind7 pind6 pind5 pind4 pind3 pind2 pind1 pind0 8 3 0x0 8 (0x2 8 ) portc portc7 portc6 portc5 portc4 portc3 portc2 portc1 portc0 8 2 0x07 (0x27) ddrc ddc7 ddc6 ddc5 ddc4 ddc3 ddc2 ddc1 ddc0 8 2 0x06 (0x26) pinc pinc7 pinc6 pinc5 pinc4 pinc3 pinc2 pinc1 pinc0 8 2 0x05 (0x25) portb portb7 portb6 portb5 portb4 portb3 portb2 portb1 portb0 8 2 0x04 (0x24) ddrb ddb7 ddb6 ddb5 ddb4 ddb3 ddb2 ddb1 ddb0 8 2 0x03 (0x23) pinb pinb7 pinb6 pinb5 pinb4 pinb3 pinb2 pinb1 pinb0 8 2 0x02 (0x22) p o rta p o rta 7 p o rta 6 p o rta 5 p o rta 4 p o rta 3 p o rta 2 p o rta 1 p o rta 0 8 1 0x01 (0x21) ddra dda7 dda6 dda5 dda4 dda3 dda2 dda1 dda0 8 1 0x00 (0x20) pina pina7 pina6 pina5 pina4 pina3 pina2 pina1 pina0 8 1 address name bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 page 340 2570n?avr?05/11 atmega325/3250/645/6450 31. instruction set summary mnemonics operands description operation flags #clocks arithmetic and logic instructions add rd, rr add two registers rd rd + rr z,c,n,v,h 1 adc rd, rr add with carry two registers rd rd + rr + c z,c,n,v,h 1 adiw rdl,k add immediate to word rdh:rdl rdh:rdl + k z,c,n,v,s 2 sub rd, rr subtract two registers rd rd - rr z,c,n,v,h 1 subi rd, k subtract constant from register rd rd - k z,c,n,v,h 1 sbc rd, rr subtract with carry two registers rd rd - rr - c z,c,n,v,h 1 sbci rd, k subtract with carry constant from reg. rd rd - k - c z,c,n,v,h 1 sbiw rdl,k subtract immediate from word rdh:rdl rdh:rdl - k z,c,n,v,s 2 and rd, rr logical and registers rd rd ? rr z,n,v 1 andi rd, k logical and register and constant rd rd ? k z,n,v 1 or rd, rr logical or registers rd rd v rr z,n,v 1 ori rd, k logical or register and constant rd rd v k z,n,v 1 eor rd, rr exclusive or registers rd rd rr z,n,v 1 com rd one?s complement rd 0xff ? rd z,c,n,v 1 neg rd two?s complement rd 0x00 ? rd z,c,n,v,h 1 sbr rd,k set bit(s) in register rd rd v k z,n,v 1 cbr rd,k clear bit(s) in register rd rd ? (0xff - k) z,n,v 1 inc rd increment rd rd + 1 z,n,v 1 dec rd decrement rd rd ? 1 z,n,v 1 tst rd test for zero or minus rd rd ? rd z,n,v 1 clr rd clear register rd rd rd z,n,v 1 ser rd set register rd 0xff none 1 mul rd, rr multiply unsigned r1:r0 rd x rr z,c 2 muls rd, rr multiply signed r1:r0 rd x rr z,c 2 mulsu rd, rr multiply signed with unsigned r1:r0 rd x rr z,c 2 fmul rd, rr fractional multiply unsigned r1:r0 (rd x rr) << 1 z,c 2 fmuls rd, rr fractional multiply signed r1:r0 (rd x rr) << 1 z,c 2 fmulsu rd, rr fractional multiply signed with unsigned r1:r0 (rd x rr) << 1 z,c 2 branch instructions rjmp k relative jump pc pc + k + 1 none 2 ijmp indirect jump to (z) pc z none 2 jmp k direct jump pc knone3 rcall k relative subroutine call pc pc + k + 1 none 3 icall indirect call to (z) pc znone3 call k direct subroutine call pc knone4 ret subroutine return pc stack none 4 reti interrupt return pc stack i 4 cpse rd,rr compare, skip if equal if (rd = rr) pc pc + 2 or 3 none 1/2/3 cp rd,rr compare rd ? rr z, n,v,c,h 1 cpc rd,rr compare with carry rd ? rr ? c z, n,v,c,h 1 cpi rd,k compare register with immediate rd ? k z, n,v,c,h 1 sbrc rr, b skip if bit in register cleared if (rr(b)=0) pc pc + 2 or 3 none 1/2/3 sbrs rr, b skip if bit in register is set if (rr(b)=1) pc pc + 2 or 3 none 1/2/3 sbic p, b skip if bit in i/o register cleared if (p(b)=0) pc pc + 2 or 3 none 1/2/3 sbis p, b skip if bit in i/o register is set if (p(b)=1) pc pc + 2 or 3 none 1/2/3 brbs s, k branch if status flag set if (sreg(s) = 1) then pc pc+k + 1 none 1/2 brbc s, k branch if status flag cleared if (sreg(s) = 0) then pc pc+k + 1 none 1/2 breq k branch if equal if (z = 1) then pc pc + k + 1 none 1/2 brne k branch if not equal if (z = 0) then pc pc + k + 1 none 1/2 brcs k branch if carry set if (c = 1) then pc pc + k + 1 none 1/2 brcc k branch if carry cleared if (c = 0) then pc pc + k + 1 none 1/2 brsh k branch if same or higher if (c = 0) then pc pc + k + 1 none 1/2 brlo k branch if lower if (c = 1) then pc pc + k + 1 none 1/2 brmi k branch if minus if (n = 1) then pc pc + k + 1 none 1/2 brpl k branch if plus if (n = 0) then pc pc + k + 1 none 1/2 brge k branch if greater or equal, signed if (n v= 0) then pc pc + k + 1 none 1/2 brlt k branch if less than zero, signed if (n v= 1) then pc pc + k + 1 none 1/2 brhs k branch if half carry flag set if (h = 1) then pc pc + k + 1 none 1/2 brhc k branch if half carry flag cleared if (h = 0) then pc pc + k + 1 none 1/2 brts k branch if t flag set if (t = 1) then pc pc + k + 1 none 1/2 341 2570n?avr?05/11 atmega325/3250/645/6450 brtc k branch if t flag cleared if (t = 0) then pc pc + k + 1 none 1/2 brvs k branch if overflow flag is set if (v = 1) then pc pc + k + 1 none 1/2 brvc k branch if overflow flag is cleared if (v = 0) then pc pc + k + 1 none 1/2 brie k branch if interrupt enabled if ( i = 1) then pc pc + k + 1 none 1/2 brid k branch if interrupt disabled if ( i = 0) then pc pc + k + 1 none 1/2 bit and bit-test instructions sbi p,b set bit in i/o register i/o(p,b) 1none2 cbi p,b clear bit in i/o register i/o(p,b) 0none2 lsl rd logical shift left rd(n+1) rd(n), rd(0) 0 z,c,n,v 1 lsr rd logical shift right rd(n) rd(n+1), rd(7) 0 z,c,n,v 1 rol rd rotate left through carry rd(0) c,rd(n+1) rd(n),c rd(7) z,c,n,v 1 ror rd rotate right through carry rd(7) c,rd(n) rd(n+1),c rd(0) z,c,n,v 1 asr rd arithmetic shift right rd(n) rd(n+1), n=0..6 z,c,n,v 1 swap rd swap nibbles rd(3..0) rd(7..4),rd(7..4) rd(3..0) none 1 bset s flag set sreg(s) 1 sreg(s) 1 bclr s flag clear sreg(s) 0 sreg(s) 1 bst rr, b bit store from register to t t rr(b) t 1 bld rd, b bit load from t to register rd(b) tnone1 sec set carry c 1c1 clc clear carry c 0 c 1 sen set negative flag n 1n1 cln clear negative flag n 0 n 1 sez set zero flag z 1z1 clz clear ze ro flag z 0 z 1 sei global interrupt enable i 1i1 cli global interrupt disable i 0 i 1 ses set signed test flag s 1s1 cls clear signed test flag s 0 s 1 sev set twos complement overflow. v 1v1 clv clear twos complement overflow v 0 v 1 set set t in sreg t 1t1 clt clear t in sreg t 0 t 1 seh set half carry flag in sreg h 1h1 clh clear half carry flag in sreg h 0 h 1 data transfer instructions mov rd, rr move between registers rd rr none 1 movw rd, rr copy register word rd+1:rd rr+1:rr none 1 ldi rd, k load immediate rd knone1 ld rd, x load indirect rd (x) none 2 ld rd, x+ load indirect and post-inc. rd (x), x x + 1 none 2 ld rd, - x load indirect and pre-dec. x x - 1, rd (x) none 2 ld rd, y load indirect rd (y) none 2 ld rd, y+ load indirect and post-inc. rd (y), y y + 1 none 2 ld rd, - y load indirect and pre-dec. y y - 1, rd (y) none 2 ldd rd,y+q load indirect with displacement rd (y + q) none 2 ld rd, z load indirect rd (z) none 2 ld rd, z+ load indirect and post-inc. rd (z), z z+1 none 2 ld rd, -z load indirect and pre-dec. z z - 1, rd (z) none 2 ldd rd, z+q load indirect with displacement rd (z + q) none 2 lds rd, k load direct from sram rd (k) none 2 st x, rr store indirect (x) rr none 2 st x+, rr store indirect and post-inc. (x) rr, x x + 1 none 2 st - x, rr store indirect and pre-dec. x x - 1, (x) rr none 2 st y, rr store indirect (y) rr none 2 st y+, rr store indirect and post-inc. (y) rr, y y + 1 none 2 st - y, rr store indirect and pre-dec. y y - 1, (y) rr none 2 std y+q,rr store indirect with displacement (y + q) rr none 2 st z, rr store indirect (z) rr none 2 st z+, rr store indirect and post-inc. (z) rr, z z + 1 none 2 st -z, rr store indirect and pre-dec. z z - 1, (z) rr none 2 std z+q,rr store indirect with displacement (z + q) rr none 2 sts k, rr store direct to sram (k) rr none 2 lpm load program memory r0 (z) none 3 lpm rd, z load program memory rd (z) none 3 lpm rd, z+ load program memory and post-inc rd (z), z z+1 none 3 spm store program memory (z) r1:r0 none - mnemonics operands description operation flags #clocks 342 2570n?avr?05/11 atmega325/3250/645/6450 in rd, p in port rd pnone1 out p, rr out port p rr none 1 push rr push register on stack stack rr none 2 pop rd pop register from stack rd stack none 2 mcu control instructions nop no operation none 1 sleep sleep (see specific descr. for sleep function) none 1 wdr watchdog reset (see specific descr. for wdr/timer) none 1 break break for on-chip debug only none n/a mnemonics operands description operation flags #clocks 343 2570n?avr?05/11 atmega325/3250/645/6450 32. ordering information notes: 1. this device can also be supplied in wafer form. please contact your local atmel sales office for detailed ordering info rmation and minimum quantities. 2. pb-free packaging alternative, complies to the european direc tive for restriction of hazardous substances (rohs direc- tive). also halide free and fully green. 3. for speed grades see figure 2 8 -1 on page 299 and figure 2 8 -2 on page 299 . 4. tape & reel 32.1 atmega325 speed (mhz) (3) power supply ordering code (2) package type (1) operational range 8 1. 8 - 5.5v atmega325v- 8 au atmega325v- 8 aur (4) atmega325v- 8 mu atmega325v- 8 mur (4) 64a 64a 64m1 64m1 industrial (-4 0 c to 8 5 c) 16 2.7 - 5.5v atmega325-16au atmega325-16aur (4) atmega325-16mu atmega325-16mur (4) 64a 64a 64m1 64m1 package type 64a 64-lead, 14 x 14 x 1.0mm, thin profil e plastic quad flat package (tqfp) 64m1 64-pad, 9 x 9 x 1.0mm, quad flat no -lead/micro lead frame package (qfn/mlf) 344 2570n?avr?05/11 atmega325/3250/645/6450 notes: 1. this device can also be supplied in wafer form. please contact your local atmel sales office for detailed ordering info rmation and minimum quantities. 2. pb-free packaging alternative, complies to the european direc tive for restriction of hazardous substances (rohs direc- tive). also halide free and fully green. 3. for speed grades see figure 2 8 -1 on page 299 and figure 2 8 -2 on page 299 . 4. tape & reel 32.2 atmega3250 speed (mhz) (3) power supply ordering code (2) package type (1) operational range 8 1. 8 - 5.5v atmega3250v- 8 au atmega3250v- 8 aur (4) 100a 100a industrial (-4 0 c to 8 5 c) 16 2.7 - 5.5v atmega3250-16au atmega3250-16aur (4) 100a 100a package type 100a 100-lead, 14 x 14 x 1.0mm, 0.5m m lead pitch, thin profile pl astic quad flat package (tqfp) 345 2570n?avr?05/11 atmega325/3250/645/6450 notes: 1. this device can also be supplied in wafer form. please contact your local atmel sales office for detailed ordering info rmation and minimum quantities. 2. pb-free packaging alternative, complies to the european direc tive for restriction of hazardous substances (rohs direc- tive). also halide free and fully green. 3. for speed grades see figure 2 8 -1 on page 299 and figure 2 8 -2 on page 299 . 4. tape & reel 32.3 atmega645 speed (mhz) (3) power supply ordering code (2) package type (1) operational range 8 1. 8 - 5.5v atmega645v- 8 au atmega645v- 8 aur (4) atmega645v- 8 mu atmega645v- 8 mur (4) 64a 64a 64m1 64m1 industrial (-4 0 c to 8 5 c) 16 2.7 - 5.5v atmega645-16au atmega645-16aur (4) atmega645-16mu atmega645-16mur (4) 64a 64a 64m1 64m1 package type 64a 64-lead, 14 x 14 x 1.0mm, thin profil e plastic quad flat package (tqfp) 64m1 64-pad, 9 x 9 x 1.0mm, quad flat no -lead/micro lead frame package (qfn/mlf) 346 2570n?avr?05/11 atmega325/3250/645/6450 notes: 1. this device can also be supplied in wafer form. please contact your local atmel sales office for detailed ordering info rmation and minimum quantities. 2. pb-free packaging alternative, complies to the european direc tive for restriction of hazardous substances (rohs direc- tive). also halide free and fully green. 3. for speed grades see figure 2 8 -1 on page 299 and figure 2 8 -2 on page 299 . 4. tape & reel 32.4 atmega6450 speed (mhz) (3) power supply ordering code (2) package type (1) operational range 8 1. 8 - 5.5v atmega6450v- 8 au atmega6450v- 8 aur (4) 100a 100a industrial (-4 0 c to 8 5 c) 16 2.7 - 5.5v atmega6450-16au atmega6450-16aur (4) 100a 100a package type 100a 100-lead, 14 x 14 x 1.0mm, 0.5m m lead pitch, thin profile pl astic quad flat package (tqfp) 347 2570n?avr?05/11 atmega325/3250/645/6450 33. packaging information 33.1 64a 2 3 25 orch a rd p a rkw a y sa n jo s e, ca 9 51 3 1 title drawing no. r rev. 64a, 64-le a d, 14 x 14 mm body s ize, 1.0 mm body thickne ss , 0. 8 mm le a d pitch, thin profile pl as tic q ua d fl a t p a ck a ge (tqfp) c 64a 2010-10-20 pin 1 identifier 0~7 pin 1 l c a1 a2 a d1 d e e1 e b common dimen s ion s (unit of me asu re = mm) s ymbol min nom max note note s : 1.thi s p a ck a ge conform s to jedec reference m s -026, v a ri a tion aeb. 2. dimen s ion s d1 a nd e1 do not incl u de mold protr us ion. allow ab le protr us ion i s 0.25 mm per s ide. dimen s ion s d1 a nd e1 a re m a xim u m pl as tic b ody s ize dimen s ion s incl u ding mold mi s m a tch. 3 . le a d copl a n a rity i s 0.10 mm m a xim u m. a ? ? 1.20 a1 0.05 ? 0.15 a2 0. 9 5 1.00 1.05 d 15.75 16.00 16.25 d1 1 3 . 9 0 14.00 14.10 note 2 e 15.75 16.00 16.25 e1 1 3 . 9 0 14.00 14.10 note 2 b 0. 3 0 ? 0.45 c 0.0 9 ? 0.20 l 0.45 ? 0.75 e 0. 8 0 typ 348 2570n?avr?05/11 atmega325/3250/645/6450 33.2 64m1 2 3 25 orch a rd p a rkw a y sa n jo s e, ca 9 51 3 1 title drawing no. r rev. 64m1 , 64-p a d, 9 x 9 x 1.0 mm body, le a d pitch 0.50 mm, h 64m1 2010-10-1 9 common dimen s ion s (unit of me asu re = mm) s ymbol min nom max note a 0. 8 0 0. 9 0 1.00 a1 ? 0.02 0.05 b 0.1 8 0.25 0. 3 0 d d2 5.20 5.40 5.60 8 . 9 0 9 .00 9 .10 8 . 9 0 9 .00 9 .10 e e2 5.20 5.40 5.60 e 0.50 b s c l0. 3 5 0.40 0.45 note s : 1. jedec s t a nd a rd mo-220, ( s aw s ing u l a tion) fig. 1, vmmd. 2. dimen s ion a nd toler a nce conform to a s mey14.5m-1 99 4. top view s ide view bottom view d e m a rked pin# 1 id s eating plane a1 c a c 0.0 8 1 2 3 k 1.25 1.40 1.55 e2 d2 b e pin #1 corner l pin #1 tr i a ngle pin #1 ch a mfer (c 0. 3 0) option a option b pin #1 notch (0.20 r) option c k k 5.40 mm expo s ed p a d, micro le a d fr a me p a ck a ge (mlf) 349 2570n?avr?05/11 atmega325/3250/645/6450 33.3 100a 2 3 25 orch a rd p a rkw a y sa n jo s e, ca 9 51 3 1 title drawing no. r rev. 100a, 100-le a d, 14 x 14 mm body s ize, 1.0 mm body thickne ss , 0.5 mm le a d pitch, thin profile pl as tic q ua d fl a t p a ck a ge (tqfp) d 100a 2010-10-20 pin 1 identifier 0~7 pin 1 l c a1 a2 a d1 d e e1 e b a ? ? 1.20 a1 0.05 ? 0.15 a2 0. 9 5 1.00 1.05 d 15.75 16.00 16.25 d1 1 3 . 9 0 14.00 14.10 note 2 e 15.75 16.00 16.25 e1 1 3 . 9 0 14.00 14.10 note 2 b 0.17 ? 0.27 c 0.0 9 ? 0.20 l 0.45 ? 0.75 e 0.50 typ note s : 1. thi s p a ck a ge conform s to jedec reference m s -026, v a ri a tion aed. 2. dimen s ion s d1 a nd e1 do not incl u de mold protr us ion. allow ab le protr us ion i s 0.25 mm per s ide. dimen s ion s d1 a nd e1 a re m a xim u m pl as tic b ody s ize dimen s ion s incl u ding mold mi s m a tch. 3 . le a d copl a n a rity i s 0.0 8 mm m a xim u m. common dimen s ion s (unit of me asu re = mm) s ymbol min nom max note 350 2570n?avr?05/11 atmega325/3250/645/6450 34. errata 34.1 errata atmega325 the revision letter in this section refers to the revision of the atmega325 device. 34.1.1 atmega325 rev. c ? interrupts may be lost when writing the timer registers in th e asynchronous timer 1. interrupts may be lost when writing the timer registers in the asynchronous timer the interrupt will be lo st if a timer register that is synchr onous timer clock is written when the asynchronous timer/counter register (tcntx) is 0x00. problem fix/ workaround always check that the asynchronous timer/counter register neither have the value 0xff nor 0x00 before writing to the asynchronous timer control register (tccrx), asynchronous timer counter register (tcntx), or asynchronous output compare register (ocrx). 34.1.2 atmega325 rev. b not sampled. 34.1.3 atmega325 rev. a ? interrupts may be lost when writing the timer registers in th e asynchronous timer 1. interrupts may be lost when writing the timer registers in the asynchronous timer the interrupt will be lo st if a timer register that is synchr onous timer clock is written when the asynchronous timer/counter register (tcntx) is 0x00. problem fix/ workaround always check that the asynchronous timer/counter register neither have the value 0xff nor 0x00 before writing to the asynchronous timer control register (tccrx), asynchronous timer counter register (tcntx), or asynchronous output compare register (ocrx). 34.2 errata atmega3250 the revision letter in this section refers to the revision of the atmega3250 device. 34.2.1 atmega3250 rev. c ? interrupts may be lost when writing the timer registers in th e asynchronous timer 1. interrupts may be lost when writing the timer registers in the asynchronous timer the interrupt will be lo st if a timer register that is synchr onous timer clock is written when the asynchronous timer/counter register (tcntx) is 0x00. problem fix/ workaround always check that the asynchronous timer/counter register neither have the value 0xff nor 0x00 before writing to the asynchronous timer control register (tccrx), asynchronous timer counter register (tcntx), or asynchronous output compare register (ocrx). 34.2.2 atmega3250 rev. b not sampled. 351 2570n?avr?05/11 atmega325/3250/645/6450 34.2.3 atmega3250 rev. a ? interrupts may be lost when writing the timer registers in th e asynchronous timer 1. interrupts may be lost when writing the timer registers in the asynchronous timer the interrupt will be lo st if a timer register that is synchr onous timer clock is written when the asynchronous timer/counter register (tcntx) is 0x00. problem fix/ workaround always check that the asynchronous timer/counter register neither have the value 0xff nor 0x00 before writing to the asynchronous timer control register (tccrx), asynchronous timer counter register (tcntx), or asynchronous output compare register (ocrx). 34.3 errata atmega645 the revision letter in this section refers to the revision of the atmega645 device. 34.3.1 atmega645 rev. a ? interrupts may be lost when writing the timer registers in th e asynchronous timer 1. interrupts may be lost when writing the timer registers in the asynchronous timer the interrupt will be lo st if a timer register that is synchr onous timer clock is written when the asynchronous timer/counter register (tcntx) is 0x00. problem fix/ workaround always check that the asynchronous timer/counter register neither have the value 0xff nor 0x00 before writing to the asynchronous timer control register (tccrx), asynchronous timer counter register (tcntx), or asynchronous output compare register (ocrx). 34.4 errata atmega6450 the revision letter in this section refers to the revision of the atmega6450 device. 34.4.1 atmega6450 rev. a ? interrupts may be lost when writing the timer registers in th e asynchronous timer 1. interrupts may be lost when writing the timer registers in the asynchronous timer the interrupt will be lo st if a timer register that is synchr onous timer clock is written when the asynchronous timer/counter register (tcntx) is 0x00. problem fix/ workaround always check that the asynchronous timer/counter register neither have the value 0xff nor 0x00 before writing to the asynchronous timer control register (tccrx), asynchronous timer counter register (tcntx), or asynchronous output compare register (ocrx). 352 2570n?avr?05/11 atmega325/3250/645/6450 35. datasheet revision history please note that the referring page numbers in this section are referring to this document. the referring revision in this section are referring to the document revision. 35.1 rev. 2570n ? 05/11 35.2 rev. 2570m ? 04/11 35.3 rev. 2570l ? 08/07 35.4 rev. 2570k ? 04/07 35.5 rev. 2570j ? 11/06 1. added atmel qtouch library support and qtouch sensing capablity features. 2. updated the last page with atmel ? trademarks and microsft windows ? trademarks. 1. removed ?preliminary? from the front page 2. removed ?disclaimer? section from the datasheet 3. updated table 2 8 -5 on page 301 ?bodlevel fuse coding(1)? 4. updated ?ordering information? on page 343 to include the ?tape & reel? devices. removed ?ai? and ?mi? devices. 5. updated ?errata? on page 350 . 6. updated the datasheet according to the atmel new drand style guide, including the last page. 1. updated ?features? on page 1 . 2. added ?data retention? on page 9 3. updated ?serial programming algorithm? on page 2 8 1 . 4. updated ?speed grades? on page 299 . 5. updated ?system and reset characteristics? on page 301 . 6. updated the register description at the end of each chapter. 1. updated ?errata? on page 350 . 1. updated table 2 8 -7 on page 304 . 2. updated note in table 2 8 -7 on page 304 . 353 2570n?avr?05/11 atmega325/3250/645/6450 35.6 rev. 2570i ? 07/06 35.7 rev. 2570h ? 06/06 35.8 rev. 2570g ? 04/06 35.9 rev. 2570f ? 03/06 35.10 rev. 2570e ? 03/06 1. updated table 15-6 on page 92 . 2. updated table 15-2 on page 97 , table 15-4 on page 97 , table 17-3 on page 124 , table 17-5 on page 125 , table 1 8 -2 on page 143 and table 1 8 -4 on page 144 . 3. updated ?fast pwm mode? on page 115 . 4. updated features in ?usi ? universal serial interface? on page 1 8 5 . 5. added ?clock speed considerations.? on page 191 . 6. updated ?errata? on page 350 . 1. updated ?calibrated internal rc oscillator? on page 29 . 2. updated ?osccal ? oscillator calibration register? on page 32 . 3. added table 2 8 -2 on page 300 . 1. updated ?calibrated internal rc oscillator? on page 29 . 1. updated ?errata? on page 350 . 1. added addresses in register descriptions. 2. updated number of genearl purpose i/o pins. 3. correction of bitnames in ?register summary? on page 336 . 4. added ?resources? on page 9 . 5. updated ?power management and sleep modes? on page 35 . 6. updated ?bit 0 ? ivce: interrupt vector change enable? on page 54 . 7. updated introduction in ?i/o-ports? on page 60 . 8 . updated 19. ?spi ? serial peripheral interface? on page 14 8 . 9. updated ?bit 6 ? acbg: analog comparator bandgap select? on page 199 . 10 updated features in ?analog to digital converter? on page 201 . 11. updated ?prescaling and conversion timing? on page 204 . 12. updated ?atmel atmega325/3250/645/6450 boot loader parameters? on page 262 . 13. updated ?dc characteristics? on page 297 . 354 2570n?avr?05/11 atmega325/3250/645/6450 35.11 rev. 2570d ? 05/05 35.12 rev. 2570c ? 11/04 35.13 rev. 2570b ? 09/04 35.14 rev. 2570a ? 09/04 1. mlf-package alternative changed to ?quad flat no-lead/micro lead frame package qfn/mlf?. 2. added ?pin change interrupt timing? on page 55 . 3. updated ?signature bytes? on page 26 8 . 4. updated table 27-15 on page 2 8 2 . 5. added figure 27-12 on page 2 8 4 . 6. updated figure 23-9 on page 209 and figure 27-5 on page 276 . 7. updated algorithm ?enter programming mode? on page 271 . 8 . added ?supply current of i/o modules? on page 311 . 9. updated ?ordering information? on page 343 . 1. ?0 - 8 mhz @ 2.7 - 5.5v; 0 - 16mhz @ 4.5 - 5.5v? on page 1 updated. 2. table 9- 8 on page 30 updated. 3. com01:0 renamed com0a1:0 in ? 8 -bit timer/counter0 with pwm? on page 8 5 . 4. prr-bit descripton added to ?16-bit timer/counter1? on page 102 , ?spi ? serial peripheral interface? on page 14 8 , and ?usart0? on page 157 . 5. ?part number? on page 225 updated. 6. ?typical characteristics? on page 306 updated. 7. ?dc characteristics? on page 297 updated. 8 . ?alternate functions of port g? on page 76 updated. 1. updated ?ordering information? on page 343 . 1. initial revision. i 2570n?avr?05/11 atmega325/3250/645/6450 table of contents features ................ ................ .............. ............... .............. .............. ............ 1 1 pin configurations ..... ................ ................. ................ ................. ............ 2 2 overview ............ ................ ................ ............... .............. .............. ............ 4 2.1 block diagram ...................................................................................................4 2.2 comparison between atmega325, atmega3250, atmega645 and atmega6450 6 2.3 pin descriptions .................................................................................................6 3 resources .............. .............. .............. ............... .............. .............. ............ 9 4 data retention .......... ................ ................ ................. ................ ............... 9 5 about code examples ........ .............. ............... .............. .............. ............ 9 6 capacitive touch sensing ................. ............... .............. .............. ............ 9 7 avr cpu core ................. ................ ................. .............. .............. .......... 10 7.1 overview ..........................................................................................................10 7.2 architectural overview .....................................................................................10 7.3 alu ? arithmetic logic unit .............................................................................11 7.4 status register ................................................................................................12 7.5 general purpose register file ........................................................................13 7.6 stack pointer ...................................................................................................14 7.7 instruction execution timing ...........................................................................14 7. 8 reset and interrupt handling ...........................................................................15 8 avr memories .......... ................ ................ ................. ................ ............. 18 8 .1 in-system reprogrammable flash program memory .....................................1 8 8 .2 sram data memory ........................................................................................19 8 .3 eeprom data memory ..... ................ ................ ................ ................ .............20 8 .4 i/o memory ......................................................................................................21 8 .5 register description ........................................................................................22 9 system clock and clock options ................ ................. .............. .......... 26 9.1 clock systems and their distribution ...............................................................26 9.2 clock sources .................................................................................................27 9.3 crystal oscillator .............................................................................................2 8 9.4 low-frequency crystal oscillator .....................................................................29 9.5 calibrated internal rc oscillator .....................................................................29 ii 2570n?avr?05/11 atmega325/3250/645/6450 9.6 external clock .................................................................................................30 9.7 clock output buffer .........................................................................................31 9. 8 timer/counter oscillator ..................................................................................31 9.9 system clock prescaler ..................................................................................32 9.10 register description ........................................................................................32 10 power management and sleep modes ........ ................. .............. .......... 35 10.1 sleep modes ....................................................................................................35 10.2 idle mode .........................................................................................................35 10.3 adc noise reduction mode ............................................................................36 10.4 power-down mode ...........................................................................................36 10.5 power-save mode ............................................................................................36 10.6 standby mode .................................................................................................37 10.7 power reduction register ...............................................................................37 10. 8 minimizing power consumption ......................................................................37 10.9 register description ........................................................................................39 11 system control and reset .... .............. .............. .............. .............. ........ 41 11.1 resetting the avr ...........................................................................................41 11.2 reset sources .................................................................................................41 11.3 power-on reset ...............................................................................................42 11.4 external reset .................................................................................................43 11.5 brown-out detection ........................................................................................43 11.6 watchdog reset ..............................................................................................44 11.7 internal voltage reference ..............................................................................44 11. 8 watchdog timer ..............................................................................................45 11.9 timed sequences for changing the configuration of the watchdog timer ....46 11.10 register description ........................................................................................47 12 interrupts ............... .............. .............. ............... .............. .............. .......... 49 12.1 interrupt vectors in atmel atmega325/3250/645/6450 ..................................49 12.2 moving interrupts between application and boot space .................................53 12.3 register description ........................................................................................53 13 external interrupts .......... ................ ................. .............. .............. .......... 55 13.1 pin change interrupt timing ............................................................................55 13.2 register description ........................................................................................56 14 i/o-ports ........ ................ ................. ................ ................. .............. .......... 60 iii 2570n?avr?05/11 atmega325/3250/645/6450 14.1 overview ..........................................................................................................60 14.2 ports as general digital i/o .............................................................................61 14.3 alternate port functions ..................................................................................66 14.4 register description ........................................................................................ 8 1 15 8-bit timer/counter0 with pw m .............. ................. ................ ............. 85 15.1 features .......................................................................................................... 8 5 15.2 overview .......................................................................................................... 8 5 15.3 timer/counter clock sources ......................................................................... 8 6 15.4 counter unit .................................................................................................... 8 7 15.5 output compare unit ....................................................................................... 8 7 15.6 compare match output unit ............................................................................ 8 9 15.7 modes of operation .........................................................................................90 15. 8 timer/counter timing diagrams .....................................................................95 15.9 register description ........................................................................................96 16 timer/counter0 and timer/ counter1 prescalers ........ .............. .......... 99 16.1 register description ......................................................................................101 17 16-bit timer/counter1 ......... .............. ............... .............. .............. ........ 102 17.1 features ........................................................................................................102 17.2 overview ........................................................................................................102 17.3 accessing 16-bit registers ............................................................................104 17.4 timer/counter clock sources .......................................................................107 17.5 counter unit ..................................................................................................10 8 17.6 input capture unit .........................................................................................109 17.7 output compare units ...................................................................................111 17. 8 compare match output unit ..........................................................................112 17.9 modes of operation .......................................................................................114 17.10 timer/counter timing diagrams ...................................................................121 17.11 register description ......................................................................................123 18 8-bit timer/counter2 with pw m and asynchronous operation ...... 130 1 8 .1 features ........................................................................................................130 1 8 .2 overview ........................................................................................................130 1 8 .3 timer/counter clock sources .......................................................................131 1 8 .4 counter unit ..................................................................................................131 1 8 .5 output compare unit .....................................................................................132 1 8 .6 compare match output unit ..........................................................................134 iv 2570n?avr?05/11 atmega325/3250/645/6450 1 8 .7 modes of operation .......................................................................................135 1 8 . 8 timer/counter timing diagrams ...................................................................139 1 8 .9 asynchronous operation of timer/counter2 .................................................141 1 8 .10 timer/counter prescaler ...............................................................................142 1 8 .11 register description ......................................................................................143 19 spi ? serial peripheral interface ......... .............. .............. ............ ........ 148 19.1 features ........................................................................................................14 8 19.2 overview ........................................................................................................14 8 19.3 ss pin functionality ......................................................................................152 19.4 data modes ...................................................................................................153 19.5 register description ......................................................................................154 20 usart0 .............. ................ .............. .............. .............. .............. ........... 157 20.1 features ........................................................................................................157 20.2 overview ........................................................................................................157 20.3 clock generation ...........................................................................................159 20.4 frame formats ..............................................................................................162 20.5 usart initialization .......................................................................................163 20.6 data transmission ? the usart transmitter ..............................................165 20.7 data reception ? the usart receiver .......................................................167 20. 8 asynchronous data reception ......................................................................171 20.9 multi-processor communication mode ..........................................................174 20.10 examples of baud rate setting .....................................................................176 20.11 register description ......................................................................................179 21 usi ? universal seri al interface ............ ................. ................ ............. 185 21.1 overview ........................................................................................................1 8 5 21.2 functional descriptions .................................................................................1 8 6 21.3 alternative usi usage ...................................................................................192 21.4 register descriptions ....................................................................................192 22 analog comparator .......... .............. .............. .............. .............. ........... 197 22.1 analog comparator multiplexed input ...........................................................19 8 22.2 register description ......................................................................................19 8 23 analog to digital converter ............. ............... .............. .............. ........ 201 23.1 features ........................................................................................................201 23.2 operation .......................................................................................................202 v 2570n?avr?05/11 atmega325/3250/645/6450 23.3 starting a conversion ....................................................................................203 23.4 prescaling and conversion timing ................................................................204 23.5 changing channel or reference selection ...................................................206 23.6 adc noise canceler .....................................................................................207 23.7 adc conversion result .................................................................................211 23. 8 register description ......................................................................................213 24 jtag interface and on-chi p debug system ............ .............. ........... 218 24.1 features ........................................................................................................21 8 24.2 overview ........................................................................................................21 8 24.3 tap ? test access port ................................................................................21 8 24.4 tap controller ...............................................................................................220 24.5 using the boundary-scan chain ....................................................................221 24.6 using the on-chip debug system .................................................................221 24.7 on-chip debug specific jtag instructions ...................................................222 24. 8 using the jtag programming capabilities ...................................................223 24.9 bibliography ...................................................................................................223 24.10 register description ......................................................................................223 25 ieee 1149.1 (jtag) boundary-scan ....... ................. ................ ........... 224 25.1 features ........................................................................................................224 25.2 system overview ...........................................................................................224 25.3 data registers ...............................................................................................224 25.4 boundary-scan specific jtag instructions ...................................................226 25.5 boundary-scan related register in i/o memory ...........................................227 25.6 boundary-scan chain ....................................................................................22 8 25.7 boundary-scan order ....................................................................................237 25. 8 boundary-scan description language files ..................................................250 26 boot loader support ? read-while-wri te self-programming ......... 251 26.1 features ........................................................................................................251 26.2 overview ........................................................................................................251 26.3 application and boot loader flash sections .................................................251 26.4 read-while-write and no read-while-write flash sections ........................252 26.5 boot loader lock bits ...................................................................................254 26.6 entering the boot loader program ................................................................255 26.7 addressing the flash during self-programming ...........................................256 26. 8 self-programming the flash ..........................................................................257 vi 2570n?avr?05/11 atmega325/3250/645/6450 26.9 register description ......................................................................................263 27 memory programming ........ .............. ............... .............. .............. ........ 265 27.1 program and data memory lock bits ...........................................................265 27.2 fuse bits ........................................................................................................266 27.3 signature bytes .............................................................................................26 8 27.4 calibration byte .............................................................................................26 8 27.5 parallel programming parameters, pin mapping, and commands ...............26 8 27.6 parallel programming ....................................................................................271 27.7 serial downloading ........................................................................................2 8 0 27. 8 programming via the jtag interface ............................................................2 8 4 28 electrical characteristics ... .............. ............... .............. .............. ........ 297 2 8 .1 absolute maximum ratings* .........................................................................297 2 8 .2 dc characteristics .........................................................................................297 2 8 .3 speed grades ...............................................................................................299 2 8 .4 clock characteristics .....................................................................................300 2 8 .5 system and reset characteristics ................................................................301 2 8 .6 spi timing characteristics ............................................................................302 2 8 .7 adc ...............................................................................................................304 29 typical characteristics .... .............. .............. .............. .............. ........... 306 29.1 active supply current ....................................................................................306 29.2 idle supply current ........................................................................................309 29.3 supply current of i/o modules ......................................................................311 29.4 power-down supply current ..........................................................................312 29.5 power-save supply current ...........................................................................313 29.6 standby supply current ................................................................................313 29.7 pin pull-up .....................................................................................................314 29. 8 pin driver strength ........................................................................................317 29.9 pin thresholds and hysteresis ......................................................................323 29.10 bod thresholds and analog comparator offset ..........................................326 29.11 internal oscillator speed ...............................................................................329 29.12 current consumption of peripheral units ......................................................331 29.13 current consumption in reset and reset pulsewidth ..................................334 30 register summary ............ .............. .............. .............. .............. ........... 336 31 instruction set summary ... .............. ............... .............. .............. ........ 340 vii 2570n?avr?05/11 atmega325/3250/645/6450 32 ordering information .......... .............. ............... .............. .............. ........ 343 32.1 atmega325 ...................................................................................................343 32.2 atmega3250 .................................................................................................344 32.3 atmega645 ...................................................................................................345 32.4 atmega6450 .................................................................................................346 33 packaging information .......... ................ ................. ................ ............. 347 33.1 64a ................................................................................................................347 33.2 64m1 ..............................................................................................................34 8 33.3 100a ..............................................................................................................349 34 errata ........... ................ ................ ................. ................ .............. ........... 350 34.1 errata atmega325 ........................................................................................350 34.2 errata atmega3250 ......................................................................................350 34.3 errata atmega645 ........................................................................................351 34.4 errata atmega6450 ......................................................................................351 35 datasheet revision history .. ................ ................. ................ ............. 352 35.1 rev. 2570n ? 05/11 .......................................................................................352 35.2 rev. 2570m ? 04/11 ......................................................................................352 35.3 rev. 2570l ? 0 8 /07 .......................................................................................352 35.4 rev. 2570k ? 04/07 .......................................................................................352 35.5 rev. 2570j ? 11/06 .......................................................................................352 35.6 rev. 2570i ? 07/06 ........................................................................................353 35.7 rev. 2570h ? 06/06 .......................................................................................353 35. 8 rev. 2570g ? 04/06 ......................................................................................353 35.9 rev. 2570f ? 03/06 .......................................................................................353 35.10 rev. 2570e ? 03/06 .......................................................................................353 35.11 rev. 2570d ? 05/05 .......................................................................................354 35.12 rev. 2570c ? 11/04 .......................................................................................354 35.13 rev. 2570b ? 09/04 .......................................................................................354 35.14 rev. 2570a ? 09/04 .......................................................................................354 table of contents.......... ................. ................ ................. ................ ........... i 2570n?avr?05/11 atmel corporation 2325 orchard parkway san jose, ca 95131 usa tel : (+1)(40 8 ) 441-0311 fax : (+1)(40 8 ) 4 8 7-2600 www.atmel.com atmel asia limited unit 1-5 & 16, 19/f bea tower, millennium city 5 41 8 kwun tong road kwun tong, kowloon hong kong tel : (+ 8 52) 2245-6100 fax : (+ 8 52) 2722-1369 atmel munich gmbh business campus parkring 4 d- 8 574 8 garching b. munich germany tel : (+49) 8 9-31970-0 fax : (+49) 8 9-3194621 atmel japan 9f, tonetsu shinkawa bldg. 1-24- 8 shinkawa chuo-ku, tokyo 104-0033 japan tel : (+ 8 1)(3) 3523-3551 fax : (+ 8 1)(3) 3523-75 8 1 ? 2011 atmel corporation. all rights reserved. atmel ? , atmel logo and combinations thereof, avr ? , qtouch ? , qmatrix ? , avr studio ? and others are registered trademarks or trade- marks of atmel corporation or its subsidiaries. windows ? and others are registered trademarks of microsoft corporation in u.s. and other countries. other terms and product names may be trademarks of others. disclaimer: the information in this document is provided in connection wi th atmel products. no license, ex press or implied, by estoppel or otherwise, to any intellectual property right is granted by this document or in connection with the sale of atmel products. except as set forth in the atmel terms and conditions of sales located on the atmel website, atmel assumes no liability whatsoever and disclaims any express, implied or statutory warranty relating to its pro ducts including, but not limited to, the implied warranty of merchantability, fitness for a particular purp ose, or non-infringement. in no even t shall atmel be liable for any direct, indirect, consequential, punitive, special 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