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this product conforms to specifications per the terms of the ramtron ramtron international corporation standard warranty. the product has completed ramtron?s internal 1850 ramtron drive, colorado springs, co 80921 qualification testing and has reached production status. (800) 545-fram, (719) 481-7000 http://www.ramtron.com rev. 3.1 july 2010 page 1 of 25 fm31l278/l276/l274/l272 3v integrated processor companion with memory features high integration device replaces multiple parts ? serial nonvolatile memory ? real-time clock (rtc) ? low voltage reset ? watchdog timer ? early power-fail warning/nmi ? two 16-bit event counters ? serial number with write-lock for security ferroelectric nonvolatile ram ? 4kb, 16kb, 64kb, and 256kb versions ? unlimited read/write endurance ? 45 year data retention ? nodelay? writes real-time clock/calendar ? backup current under 1 a ? seconds through centuries in bcd format ? tracks leap years through 2099 ? uses standard 32.768 khz crystal (12.5pf) ? software calibration ? supports battery or capacitor backup processor companion ? active-low reset output for v dd and watchdog ? programmable v dd reset trip point ? manual reset filtered and debounced ? programmable watchdog timer ? dual battery-backed event counter tracks system intrusions or other events ? comparator for early power-fail interrupt ? 64-bit programmable serial number with lock fast two-wire serial interface ? up to 1 mhz maximum bus frequency ? supports legacy timing for 100 khz & 400 khz ? device select pins for up to 4 memory devices ? rtc, supervisor controlled via 2-wire interface easy to use configurations ? operates from 2.7 to 3.6v ? 14-pin ?green?/rohs soic package (-g) ? low operating current ? -40 c to +85 c operation ? underwriters laboratory (ul) recognized description the fm31l27x is a family of integrated devices that includes the most commonly needed functions for processor-based systems. major features include nonvolatile memory available in various sizes, real- time clock, low-vdd reset, watchdog timer, nonvolatile event counter, lockable 64-bit serial number area, and general purpose comparator that can be used for an early power-fail (nmi) interrupt or other purpose. the family operates from 2.7 to 3.6v. each fm31l27x provides nonvolatile ram available in sizes including 4kb, 16kb, 64kb, and 256kb versions. fast write speed and unlimited endurance allow the memory to serve as extra ram or conventional nonvolatile storage. this memory is truly nonvolatile rather than battery backed. the real-time clock (rtc) provides time and date information in bcd format. it can be permanently powered from external backup voltage source, either a battery or a capacitor. the timekeeper uses a common external 32.768 khz crystal and provides a calibration mode that allows software adjustment of timekeeping accuracy. the processor companion includes commonly needed cpu support functions. supervisory functions include a reset output signal controlled by either a low vdd condition or a watchdog timeout. /rst goes active when vdd drops below a programmable threshold and remains active for 100 ms after vdd rises above the trip point. a programmable watchdog timer runs from 100 ms to 3 seconds. the watchdog timer is optional, but if enabled it will assert the reset signal for 100 ms if not restarted by the host before the timeout. a flag-bit indicates the source of the reset. a general-purpose comparator compares an external input pin to the onboard 1.2v reference. this is useful for generating a power-fail interrupt (nmi) but can be used for any purpose. the family also includes a programmable 64-bit serial number that can be locked making it unalterable. additionally it offers a dual battery-backed event counter that tracks the number of rising or falling edges detected on dedicated input pins.
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 2 of 25 pin configuration pin name function cnt1, cnt2 event counter inputs a0, a1 device select inputs cal/pfo clock calibration and early power-fail output /rst reset input/output pfi early power-fail input x1, x2 crystal connections sda serial data scl serial clock vbak battery-backup supply vdd supply voltage vss ground ordering information base configuration memory size operating voltage reset threshold ordering part number fm31l278 256kb 2.7-3.6v 2.6v, 2.9v fm31l278-g 256kb 2.7-3.6v 2.6v, 2.9v FM31L278-GTR (tape&reel) fm31l276 64kb 2.7-3.6v 2.6v, 2.9v fm31l276-g 64kb 2.7-3.6v 2.6v, 2.9v fm31l276-gtr (tape&reel) fm31l274 16kb 2.7-3.6v 2.6v, 2.9v fm31l274-g 16kb 2.7-3.6v 2.6v, 2.9v fm31l274-gtr (tape&reel) fm31l272 4kb 2.7-3.6v 2.6v, 2.9v fm31l272-g 4kb 2.7-3.6v 2.6v, 2.9v fm31l272-gtr (tape&reel) other memory configurations may be available. please contact the factory for more information. vdd vbak scl sda vss x1 x2 cal/pfo cnt1 pfi rst a0 a1 cnt2 1 2 3 4 5 6 7 14 13 12 11 10 9 8
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 3 of 25 figure 1. block diagram pin descriptions pin name type pin description a0, a1 input device select inputs are used to address multiple memories on a serial bus. to select the device the address value on the two pins must match the corresponding bits contained in the device address. the device select pins are pulled down internally. cnt1, cnt2 input event counter inputs: these battery-backed inputs increment counters when an edge is detected on the corresponding cnt pin. the polarity is programmable. these pins should not be left floating. tie to ground if these pins are not used. cal/pfo output in calibration mode, this pin supplies a 512 hz square-wave output for clock calibration. in normal operation, this is the early power-fail output. x1, x2 i/o 32.768 khz crystal connection. when using an external oscillator, apply the clock to x1 and a dc mid-level to x2 (see crystal oscillator section for suggestions). /rst i/o active low reset output with weak pull-up. also input for manual reset. sda i/o serial data & address: this is a bi-directional line for the two-wire interface. it is open- drain and is intended to be wire-or?d with other devices on the two-wire bus. the input buffer incorporates a schmitt trigger for noise immunity and the output driver includes slope control for falling edges. a pull-up resistor is required. scl input serial clock: the serial clock line for the two-wire interface. data is clocked out of the part on the falling edge, and in on the rising edge. the scl input also incorporates a schmitt trigger input for noise immunity. pfi input early power-fail input: typically connected to an unregulated power supply to detect an early power failure. this pin should not be left floating. vbak supply backup supply voltage: a 3v battery or a large value capacitor. if no backup supply is used, this pin should be tied to ground and the vbc bit should be cleared. the trickle charger is ul recognized and ensures no excessive current when using a lithium battery. vdd supply supply voltage vss supply ground f-ram array 2-wire interface scl sda rst a1, a0 cal/pfo pfi vdd vbak rtc 2.5v - + rtc re g isters event counters cnt1 cnt2 special function registers s/n x1 x2 lockout lockout + - 1.2v watchdog lv detect switched power 512hz rtc cal. battery backed nonvolatile
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 4 of 25 overview the fm31l27x family combines a serial nonvolatile ram with a real-time clock (rtc) and a processor companion. the companion is a highly integrated peripheral including a processor supervisor, a comparator used for early power-fail warning, nonvolatile event counters, and a 64-bit serial number. the fm31l27x integrates these complementary but distinct functions that share a common interface in a single package. although monolithic, the product is organized as two logical devices, the f-ram memory and the rtc/companion. from the system perspective they appear to be two separate devices with unique ids on the serial bus. the memory is organized as a stand-alone 2-wire nonvolatile memory with a standard device id value. the real-time clock and supervisor functions are accessed with a separate 2-wire device id. this allows clock/calendar data to be read while maintaining the most recently used memory address. the clock and supervisor functions are controlled by 25 special function registers. the rtc and event counter circuits are maintained by the power source on the vbak pin, allowing them to operate from battery or backup capacitor power when v dd drops below an internally set threshold. each functional block is described below. memory operation the fm31l27x is a family of products available in different memory sizes including 4kb, 16kb, 64kb, and 256kb. the family is software compatible, all versions use consistent two-byte addressing for the memory device. this makes the lowest density device different from its stand-alone memory counterparts but makes them compatible within the entire family. memory is organized in bytes, for example the 4kb memory is 512 x 8 and the 256kb memory is 32,768 x 8. the memory is based on f-ram technology. therefore it can be treated as ram and is read or written at the speed of the two-wire bus with no delays for write operations. it also offers effectively unlimited write endurance unlike other nonvolatile memory technologies. the 2-wire interface protocol is described further on page 13. the memory array can be write-protected by software. two bits in the processor companion area (wp0, wp1 in register 0bh) control the protection setting as shown in the following table. based on the setting, the protected addresses cannot be written and the 2-wire interface will not acknowledge any data to protected addresses. the special function registers containing these bits are described in detail below. write protect addresses wp1 wp0 none 0 0 bottom 1/4 0 1 bottom 1/2 1 0 full array 1 1 processor companion in addition to nonvolatile ram, the fm31l27x family incorporates a highly integrated processor companion. it includes a low voltage reset, a programmable watchdog timer, battery-backed event counters, a comparator for early power-fail detection or other purposes, and a 64-bit serial number. processor supervisor supervisors provide a host processor two basic functions: detection of power supply fault conditions and a watchdog timer to escape a software lockup condition. all fm31l27x devices have a reset pin (/rst) to drive the processor reset input during power faults (and power-up) and software lockups. it is an open drain output with a weak internal pull-up to v dd . this allows other reset sources to be wire- or?d to the /rst pin. when v dd is above the programmed trip point, /rst output is pulled weakly to v dd . if v dd drops below the reset trip point voltage level (v tp ) the /rst pin will be driven low. it will remain low until v dd falls too low for circuit operation which is the v rst level. when v dd rises again above v tp , /rst will continue to drive low for at least 100 ms (t rpu ) to ensure a robust system reset at a reliable v dd level. after t rpu has been met, the /rst pin will return to the weak high state. while /rst is asserted, serial bus activity is locked out even if a transaction occurred as v dd dropped below v tp . a memory operation started while v dd is above v tp will be completed internally. figure 2 below illustrates the reset operation in response to the v dd voltage. figure 2. low voltage reset the bit vtp controls the trip point of the low voltage detect circuit. it is located in register 0bh, bit 0. note that the bit 1 location is a ?don?t care?. vdd vtp t rpu rst
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 5 of 25 v tp vtp 2.6v 0 2.9v 1 the watchdog timer can also be used to assert the reset signal (/rst). the watchdog is a free running programmable timer. the period can be software programmed from 100 ms to 3 seconds in 100 ms increments via a 5-bit nonvolatile register. all programmed settings are minimum values and vary with temperature according to the operating specifications. the watchdog has two additional controls associated with its operation, a watchdog enable bit (wde) and timer restart bits (wr). both the enable bit must be set and the watchdog must timeout in order to drive /rst active. if a reset event occurs, the timer will automatically restart on the rising edge of the reset pulse. if wde=0, the watchdog timer runs but a watchdog fault will not cause /rst to be asserted low. the wtr flag will be set, indicating a watchdog fault. this setting is useful during software development and the developer does not want /rst to drive. note that setting the maximum timeout setting (11111b) disables the counter to save power. the second control is a nibble that restarts the timer preventing a reset. the timer should be restarted after changing the timeout value. the watchdog timeout value is located in register 0ah, bits 4-0, and the watchdog enable is bit 7. the watchdog is restarted by writing the pattern 1010b to the lower nibble of register 09h. writing this pattern will also cause the timer to load new timeout values. writing other patterns to this address will not affect its operation. note the watchdog timer is free- running. prior to enabling it, users should restart the timer as described above. this assures that the full timeout period will be set immediately after enabling. the watchdog is disabled when v dd is below v tp . the following table summarizes the watchdog bits. a block diagram follows. watchdog timeout wdt4-0 0ah, bits 4-0 watchdog enable wde 0ah, bit 7 watchdog restart wr3-0 09h, bits 3-0 figure 3. watchdog timer manual reset the /rst pin is bi-directional and allows the fm31l27x to filter and de-bounce a manual reset switch. the /rst input detects an external low condition and responds by driving the /rst signal low for 100 ms. figure 4. manual reset note that an internal weak pull-up on /rst eliminates the need for additional external components. reset flags in case of a reset condition, a flag will be set to indicate the source of the reset. a low v dd reset is indicated by the por flag, register 09h bit 6. a watchdog reset is indicated by the wtr flag, register 09h bit 7. note that the flags are internally set in response to reset sources, but they must be cleared by the user. when the register is read, it is possible that both flags are set if both have occurred since the user last cleared them. early power fail comparator an early power fail warning can be provided to the processor well before v dd drops out of spec. the comparator is used to create a power fail interrupt (nmi). this can be accomplished by connecting the pfi pin to the unregulated power supply via a resistor divider. an application circuit is shown below. figure 5. comparator as early power-fail warning + - 1.2v ref regulato r vdd fm31l27x to mcu nmi input cal/pfo pfi timebase counter watchdog timeou t 100 ms clock wde /rst wr3-0 = 1010b to restart fm31l27x reset switch rst mcu switch behavio r rst fm31l27x drives 100 ms (min.)
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 6 of 25 the voltage on the pfi input pin is compared to an onboard 1.2v reference. when the pfi input voltage drops below this threshold, the comparator will drive the cal/pfo pin to a low state. the comparator has 100 mv (max) of hysteresis to reduce noise sensitivity, only for a rising pfi signal. for a falling pfi edge, there is no hysteresis. the comparator is a general purpose device and its application is not limited to the nmi function. the comparator is not integrated into the special function registers except as it shares its output pin with the cal output. when the rtc calibration mode is invoked by setting the cal bit (register 00h, bit 2), the cal/pfo output pin will be driven with a 512 hz square wave and the comparator will be ignored. since most users only invoke the calibration mode during production, this should have no impact on system operations using the comparator. note: the maximum voltage on the comparator input pfi is limited to 3.75v under normal operating conditions. event counter the fm31l27x offers the user two battery-backed event counters. input pins cnt1 and cnt2 are programmable edge detectors. each clocks a 16-bit counter. when an edge occurs, the counters will increment their respective registers. counter 1 is located in registers 0dh and 0eh, counter 2 is located in registers 0fh and 10h. these register values can be read anytime vdd is above vtp, and they will be incremented as long as a valid vbak power source is provided. to read, set the rc bit register 0ch bit 3 to 1. this takes a snapshot of all four counter bytes allowing a stable value even if a count occurs during the read. the registers can be written by software allowing the counters to be cleared or initialized by the system. counts are blocked during a write operation. the two counters can be cascaded to create a single 32-bit counter by setting the cc control bit (register 0ch). when cascaded, the cnt1 input will cause the counter to increment. cnt2 is not used in this mode. figure 6. event counter the control bits for event counting are located in register 0ch. counter 1 polarity is bit c1p, bit 0; counter 2 polarity is c2p, bit 1; the cascade control is cc, bit 2; and the read counter bit is rc bit 3. the polarity bits must be set prior to setting the counter value(s). if a polarity bit is changed, the counter may inadvertently increment. if the counter pins are not being used, tie them to ground. serial number a memory location to write a 64-bit serial number is provided. it is a writeable nonvolatile memory block that can be locked by the user once the serial number is set. the 8 bytes of data and the lock bit are all accessed via the device id for the processor companion. therefore the serial number area is separate and distinct from the memory array. the serial number registers can be written an unlimited number of times, so these locations are general purpose memory. however once the lock bit is set the values cannot be altered and the lock cannot be removed. once locked the serial number registers can still be read by the system. the serial number is located in registers 11h to 18h. the lock bit is snl, register 0bh bit 7. setting the snl bit to a 1 disables writes to the serial number registers, and the snl bit cannot be cleared . real-time clock operation the real-time clock (rtc) is a timekeeping device that can be battery or capacitor backed for permanently-powered operation. it offers a software calibration feature that allows high accuracy. the rtc consists of an oscillator, clock divider, and a register system for user access. it divides down the 32.768 khz time-base and provides a minimum resolution of seconds (1hz). static registers provide the user with read/write access to the time values. it includes registers for seconds, minutes, hours, day- of-the-week, date, months, and years. a block diagram (figure 7) illustrates the rtc function. the user registers are synchronized with the timekeeper core using r and w bits in register 00h described below. changing the r bit from 0 to 1 transfers timekeeping information from the core into holding registers that can be read by the user. if a timekeeper update is pending when r is set, then the core will be updated prior to loading the user registers. the registers are frozen and will not be updated again until the r bit is cleared to 0. r is used for reading the time. setting the w bit to 1 locks the user registers. clearing it to 0 causes the values in the user registers 16-bit counte r cnt1 cc cnt2 c1p c2p 16-bit counte r
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 7 of 25 to be loaded into the timekeeper core. w is used for writing new time values. users should be certain not to load invalid values, such as ffh, to the timekeeping registers. updates to the timekeeping core occur continuously except when locked. backup power the real-time clock/calendar is intended to be permanently powered. when the primary system power fails, the voltage on the v dd pin will drop. when v dd is less 2.5v the rtc (and event counters) will switch to the backup power supply on v bak . the clock operates at extremely low current in order to maximize battery or capacitor life. however, one of the advantages of combining a clock function with the f-ram memory is that data is not lost regardless of the backup power source. a battery may be inserted into a system board without any concern for excessive current draw on the fm31l27x?s v bak pin. trickle charger to facilitate capacitor backup the v bak pin can optionally provide a trickle charge current. when the vbc bit, register 0bh bit 2, is set to ?1?, the v bak pin will source approximately 80 a until v bak reaches v dd . this charges the capacitor to v dd without an external diode and resistor charger. there is a fast charge mode which is enabled by the fc bit (register 0bh, bit 5). in this mode the trickle charger current is set to approximately 1 ma, allowing a large backup capacitor to charge more quickly. in the case where no backup supply is used, the v bak pin should be tied to v ss . be sure to turn off the trickle charger (vbc=0), otherwise charger current will be shunted to ground from v dd . , , , , note: systems using lithium batteries should clear the vbc bit to 0 to prevent battery charging. the v bak circuitry includes an internal 1 k ? series resistor as a safety element. the trickle charger is ul recognized. figure 7. real-time clock core block diagram calibration when the cal bit in a register 00h is set to 1, the clock enters calibration mode. in calibration mode, the cal/pfo output pin is dedicated to the calibration function and the power fail output is temporarily unavailable. calibration operates by applying a digital correction to the counter based on the frequency error. in this mode, the cal/pfo pin is driven with a 512 hz (nominal) square wave. any measured deviation from 512 hz translates into a timekeeping error. the user converts the measured error in ppm and writes the appropriate correction value to the calibration register. the correction factors are listed in the table below. positive ppm errors require a negative adjustment that removes pulses. negative ppm errors require a positive correction that adds pulses. positive ppm adjustments have the cals (sign) bit set to 1, where as negative ppm adjustments have cals = 0. after calibration, the clock will have a maximum error of 2.17 ppm or 0.09 minutes per month at the calibrated temperature. the calibration setting is stored in f-ram so is not lost should the backup source fail. it is accessed with bits cal.4-0 in register 01h. this value only can be written when the cal bit is set to a 1. to exit the calibration mode, the user must clear the cal bit to a 0. when the cal bit is 0, the cal/pfo pin will revert to the power fail output function. 32.768 khz crystal oscillato r cloc k divide r update logic 512 hz w r seconds 7 bits minutes 7 bits hours 6 bits date 6 bits months 5 bits years 8 bits cf days 3 bits user interface registers 1 hz /oscen
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 8 of 25 crystal oscillator the crystal oscillator is designed to use a 12.5pf crystal without the need for external components, such as loading capacitors. the fm31l27x device has built-in loading capacitors that match the crystal. if a 32.768khz crystal is not used, an external oscillator may be connected to the fm31l27x. apply the oscillator to the x1 pin. its high and low voltage levels can be driven rail-to-rail or amplitudes as low as approximately 500mv p-p. to ensure proper operation, a dc bias must be applied to the x2 pin. it should be centered between the high and low levels on the x1 pin. this can be accomplished with a voltage divider. in the example, r1 and r2 are chosen such that the x2 voltage is centered around the x1 oscillator drive levels. if you wish to avoid the dc current, you may choose to drive x1 with an external clock and x2 with an inverted clock using a cmos inverter. figure 8. external oscillator layout requirements the x1 and x2 crystal pins employ very high impedance circuits and the oscillator connected to these pins can be upset by noise or extra loading. to reduce rtc clock errors from signal switching noise, a guard ring must be placed around these pads and the guard ring grounded. sda and scl traces should be routed away from the x1/x2 pads. the x1 and x2 trace lengths should be less than 5 mm. the use of a ground plane on the backside or inner board layer is preferred. see layout example. red is the top layer, green is the bottom layer. layout for surface mount crystal layout for through hole crystal (red = top layer, green = bottom layer) (red = top layer, green = bottom layer) x1 x2 vd d fm31l27x r1 r2 vdd scl sda x2 x1 pfi vbak vdd scl sda x2 x1 pfi vbak
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 9 of 25 calibration adjustments positive calibration for slow clocks: calibration will achieve 2.17 ppm after calibration measured frequency range error range (ppm) min max min max program calibration register to: 0 512.0000 511.9989 0 2.17 000000 1 511.9989 511.9967 2.18 6.51 100001 2 511.9967 511.9944 6.52 10.85 100010 3 511.9944 511.9922 10.86 15.19 100011 4 511.9922 511.9900 15.20 19.53 100100 5 511.9900 511.9878 19.54 23.87 100101 6 511.9878 511.9856 23.88 28.21 100110 7 511.9856 511.9833 28.22 32.55 100111 8 511.9833 511.9811 32.56 36.89 101000 9 511.9811 511.9789 36.90 41.23 101001 10 511.9789 511.9767 41.24 45.57 101010 11 511.9767 511.9744 45.58 49.91 101011 12 511.9744 511.9722 49.92 54.25 101100 13 511.9722 511.9700 54.26 58.59 101101 14 511.9700 511.9678 58.60 62.93 101110 15 511.9678 511.9656 62.94 67.27 101111 16 511.9656 511.9633 67.28 71.61 110000 17 511.9633 511.9611 71.62 75.95 110001 18 511.9611 511.9589 75.96 80.29 110010 19 511.9589 511.9567 80.30 84.63 110011 20 511.9567 511.9544 84.64 88.97 110100 21 511.9544 511.9522 88.98 93.31 110101 22 511.9522 511.9500 93.32 97.65 110110 23 511.9500 511.9478 97.66 101.99 110111 24 511.9478 511.9456 102.00 106.33 111000 25 511.9456 511.9433 106.34 110.67 111001 26 511.9433 511.9411 110.68 115.01 111010 27 511.9411 511.9389 115.02 119.35 111011 28 511.9389 511.9367 119.36 123.69 111100 29 511.9367 511.9344 123.70 128.03 111101 30 511.9344 511.9322 128.04 132.37 111110 31 511.9322 511.9300 132.38 136.71 111111 negative calibration for fast clocks: calibration will achieve 2.17 ppm after calibration measured frequency range error range (ppm) min max min max program calibration register to: 0 512.0000 512.0011 0 2.17 000000 1 512.0011 512.0033 2.18 6.51 000001 2 512.0033 512.0056 6.52 10.85 000010 3 512.0056 512.0078 10.86 15.19 000011 4 512.0078 512.0100 15.20 19.53 000100 5 512.0100 512.0122 19.54 23.87 000101 6 512.0122 512.0144 23.88 28.21 000110 7 512.0144 512.0167 28.22 32.55 000111 8 512.0167 512.0189 32.56 36.89 001000 9 512.0189 512.0211 36.90 41.23 001001 10 512.0211 512.0233 41.24 45.57 001010 11 512.0233 512.0256 45.58 49.91 001011 12 512.0256 512.0278 49.92 54.25 001100 13 512.0278 512.0300 54.26 58.59 001101 14 512.0300 512.0322 58.60 62.93 001110 15 512.0322 512.0344 62.94 67.27 001111 16 512.0344 512.0367 67.28 71.61 010000 17 512.0367 512.0389 71.62 75.95 010001 18 512.0389 512.0411 75.96 80.29 010010 19 512.0411 512.0433 80.30 84.63 010011 20 512.0433 512.0456 84.64 88.97 010100 21 512.0456 512.0478 88.98 93.31 010101 22 512.0478 512.0500 93.32 97.65 010110 23 512.0500 512.0522 97.66 101.99 010111 24 512.0522 512.0544 102.00 106.33 011000 25 512.0544 512.0567 106.34 110.67 011001 26 512.0567 512.0589 110.68 115.01 011010 27 512.0589 512.0611 115.02 119.35 011011 28 512.0611 512.0633 119.36 123.69 011100 29 512.0633 512.0656 123.70 128.03 011101 30 512.0656 512.0678 128.04 132.37 011110 31 512.0678 512.0700 132.38 136.71 011111
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 10 of 25 register map the rtc and processor companion functions are accessed via 25 special function registers mapped to a separate 2- wire device id. the interface protocol is described below. the registers contain timekeeping data, control bits, or information flags. a description of each register follows the summary table below. register map summary table nonvolatile = battery-backed = address d7 d6 d5 d4 d3 d2 d1 d0 function range serial number b y te 7 serial number 7 ffh serial number byte 6 serial number 6 ffh serial number b y te 5 serial number 5 ffh serial number byte 4 serial number 4 ffh serial number b y te 3 serial number 3 ffh serial number b y te 2 serial number 2 ffh serial number byte 1 serial number 1 ffh serial number b y te 0 serial number 0 ffh 10h counter 2 msb event counter 2 msb ffh 0fh counter 2 lsb event counter 2 lsb ffh 0eh counter 1 msb event counter 1 msb ffh 0dh counter 1 lsb event counter 1 lsb ffh 0ch rc cc c2p c1p event count control 0bh snl - fc wp1 wp0 vbc - vtp companion control 0ah wde - - wdt4 wdt3 wdt2 wdt1 wdt0 watchdog control 09h wtr por lb - wr3 wr2 wr1 wr0 watchdo g restart/fla g s 08h 10 years years years 00-99 07h 0 0 0 10 mo months month 1-12 06h 00 10 date date date 1-31 05h 00000 day day 1-7 04h 00 10 hours hours hours 0-23 03h 0 10 minutes minutes minutes 0-59 02h 0 10 seconds seconds seconds 0-59 01h /oscen reserved cals cal4 cal3 cal2 cal1 cal0 cal/control 00h reserved cf reserved reserved reserved cal w r rtc control 18h 17h 11h 16h 15h 14h 13h 12h note: when the device is first powered up and programmed, all registers must be written because the battery- backed register values cannot be guaranteed. the table below shows the default values of the non-volatile registers. all other register values should be treated as unknown. default register values address hex value 18h 0x00 17h 0x00 16h 0x00 15h 0x00 14h 0x00 13h 0x00 12h 0x00 11h 0x00 0bh 0x00 0ah 0x1f 01h 0x80
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 11 of 25 register description address description 18h serial number byte 7 d7 d6 d5 d4 d3 d2 d1 d0 sn.63 sn.62 sn.61 sn.60 sn.59 sn.58 sn.57 sn.56 upper byte of the serial number. read/write when snl=0, read-only when snl=1. nonvolatile. 17h serial number byte 6 d7 d6 d5 d4 d3 d2 d1 d0 sn.55 sn.54 sn.53 sn.52 sn.51 sn.50 sn.49 sn.48 byte 6 of the serial number. read/write when snl=0, read-only when snl=1. nonvolatile. 16h serial number byte 5 d7 d6 d5 d4 d3 d2 d1 d0 sn.47 sn.46 sn.45 sn.44 sn.43 sn.42 sn.41 sn.40 byte 5 of the serial number. read/write when snl=0, read-only when snl=1. nonvolatile. 15h serial number byte 4 d7 d6 d5 d4 d3 d2 d1 d0 sn.39 sn.38 sn.37 sn.36 sn.35 sn.34 sn.33 sn.32 byte 4 of the serial number. read/write when snl=0, read-only when snl=1. nonvolatile. 14h serial number byte 3 d7 d6 d5 d4 d3 d2 d1 d0 sn.31 sn.30 sn.29 sn.28 sn.27 sn.26 sn.25 sn.24 byte 3 of the serial number. read/write when snl=0, read-only when snl=1. nonvolatile. 13h serial number byte 2 d7 d6 d5 d4 d3 d2 d1 d0 sn.23 sn.22 sn.21 sn.20 sn.19 sn.18 sn.17 sn.16 byte 2 of the serial number. read/write when snl=0, read-only when snl=1. nonvolatile. 12h serial number byte 1 d7 d6 d5 d4 d3 d2 d1 d0 sn.15 sn.14 sn.13 sn.12 sn.11 sn.10 sn.9 sn.8 byte 1 of the serial number. read/write when snl=0, read-only when snl=1. nonvolatile. 11h serial number byte 0 d7 d6 d5 d4 d3 d2 d1 d0 sn.7 sn.6 sn.5 sn.4 sn.3 sn.2 sn.1 sn.0 lsb of the serial number. read/write when snl=0, read-only when snl=1. nonvolatile. 10h counter 2 msb d7 d6 d5 d4 d3 d2 d1 d0 c2.15 c2.14 c2.13 c2.12 c2.11 c2.10 c2.9 c2.8 event counter 2 msb. increments on overflows from counter 2 lsb. battery-backed, read/write. 0fh counter 2 lsb d7 d6 d5 d4 d3 d2 d1 d0 c2.7 c2.6 c2.5 c2.4 c2.3 c2.2 c2.1 c2.0 event counter 2 lsb. increments on programmed edge event on cnt2 input or overflows from counter 1 msb when cc=1. battery-backed, read/write . 0eh counter 1 msb d7 d6 d5 d4 d3 d2 d1 d0 c1.15 c1.14 c1.13 c1.12 c1.11 c1.10 c1.9 c1.8 event counter 1 msb. increments on overflows from counter 1 lsb. battery-backed, read/write. 0dh counter 1 lsb d7 d6 d5 d4 d3 d2 d1 d0 c1.7 c1.6 c1.5 c1.4 c1.3 c1.2 c1.1 c1.0 event counter 1 lsb. increments on programmed edge event on cnt1 input. battery-backed, read/write.
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 12 of 25 0ch event counter control d7 d6 d5 d4 d3 d2 d1 d0 - - - - rc cc c2p c1p rc read counter. setting this bit to 1 takes a snapshot of the four counters bytes allowing the system to read the values without missing count events. the rc bit will be automatically cleared. cc counter cascade. when cc=0, the event counters operate independently according to the edge programmed by c1p and c2p respectively. when cc=1, the counters are cascaded to create one 32-bit counter. the registers of counter 2 represent the most significant 16-bits of the counter and cnt1 is the controlling input. bit c2p is ?don?t care? when cc=1. battery-backed, read/write. c2p cnt2 detects falling edges when c2p = 0, rising edges when c2p = 1. c2p is ?don?t care? when cc=1. the value of event counter 2 may inadvertently increment if c2p is changed. battery-backed, read/write. c1p cnt1 detects falling edges when c1p = 0, rising edges when c1p = 1. the value of event counter 1 may inadvertently increment if c1p is changed. battery-backed, read/write. 0bh companion control d7 d6 d5 d4 d3 d2 d1 d0 snl - fc wp1 wp0 vbc - vtp snl serial number lock. setting to a 1 makes registers 11h to 18h and snl permanently read-only. snl cannot be cleared once set to 1. nonvolatile, read/write. fc fast charge: setting fc to ?1? (and vbc=1) causes a ~1 ma trickle charge current to be supplied on v bak . clearing vbc to ?0? disables the charge current. nonvolatile, read/write. wp1-0 write protect. these bits control the write protection of the memory array. nonvolatile, read/write. write protect addresses wp1 wp0 none 0 0 bottom 1/4 0 1 bottom 1/2 1 0 full array 1 1 vbc vbak charger control. setting vbc to ?1? (and fc=0) causes a ~80 a (1 ma if fc=1) trickle charge current to be supplied on v ba k . clearing vbc to ?0? disables the charge current. nonvolatile, read/write. vtp vtp select. this bit controls the reset trip point for the low vdd reset function. nonvolatile, read/write. trip voltage vtp 2.6v 0 2.9v 1 0ah watchdog control d7 d6 d5 d4 d3 d2 d1 d0 wde - - wdt4 wdt3 wdt2 wdt1 wdt0 wde watchdog enable. when wde=1, a watchdog timer fault will cause the /rst signal to go active. when wde = 0 the timer runs but has no effect on /rst, however the wtr flag will be set when a fault occurs. note as the timer is free-running, users should restart the timer using wr3-0 prior to setting wde=1. this assures a full watchdog timeout interval occurs. nonvolatile, read/write. wdt4-0 watchdog timeout. indicates the minimum watchdog timeout interval with 100 ms resolution. new watchdog timeouts are loaded when the timer is restarted by writing the 1010b pattern to wr3-0. nonvolatile, read/write. watchdog timeout wdt4 wdt3 wdt2 wdt1 wdt0 invalid ? default 100 ms 0 0 0 0 0 100 ms 0 0 0 0 1 200 ms 0 0 0 1 0 300 ms 0 0 0 1 1 . . . 2000 ms 1 0 1 0 0 2100 ms 1 0 1 0 1 2200 ms 1 0 1 1 0 . . . 2900 ms 1 1 1 0 1 3000 ms 1 1 1 1 0 disable counter 1 1 1 1 1
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 13 of 25 09h watchdog restart & flags d7 d6 d5 d4 d3 d2 d1 d0 wtr por lb - wr3 wr2 wr1 wr0 wtr watchdog timer reset flag: when a watchdog timer fault occurs, the wtr bit will be set to 1. it must be cleared by the user. note that both wtr and por could be set if both reset sources have occurred since the flags were cleared by the user. battery-backed. read/write (internally set, user can clear bit). por power-on reset flag: when the /rst pin is activated by v dd < v tp , the por bit will be set to 1. it must be cleared by the user. note that both wtr and por could be set if both reset sources have occurred since the flags were cleared by the user. battery-backed. read/write (internally set, user can clear bit). lb low backup flag: on power up, if the vbak source is below the minimum voltage to operate the rtc and event counters, this bit will be set to 1. the user should clear it to 0 when initializing the system. battery-backed. read/write (internally set, user can clear bit). wr3-0 watchdog restart: writing a pattern 1010b to wr3-0 restarts the watchdog timer. the upper nibble contents do not affect this operation. writing any pattern other than 1010b to wr3-0 has no effect on the timer. this allows users to clear the wtr, por, and lb flags without affecting the watchdog timer. battery-backed, write-only. 08h timekeeping ? years d7 d6 d5 d4 d3 d2 d1 d0 10 year.3 10 year.2 10 year.1 10 year.0 year.3 year.2 year.1 year.0 contains the lower two bcd digits of the year. lower nibble contains the value for years; upper nibble contains the value for 10s of years. each nibble operates from 0 to 9. the range for the register is 0-99. battery-backed, read/write. 07h timekeeping ? months d7 d6 d5 d4 d3 d2 d1 d0 0 0 0 10 month month.3 month.2 month.1 month.0 contains the bcd digits for the month. lower nibble contains the lower digit and operates from 0 to 9; upper nibble (one bit) contains the upper digit and operates from 0 to 1. the range for the register is 1-12. battery- backed, read/write. 06h timekeeping ? date of the month d7 d6 d5 d4 d3 d2 d1 d0 0 0 10 date.1 10 date.0 date.3 date.2 date.1 date.0 contains the bcd digits for the date of the month. lower nibble contains the lower digit and operates from 0 to 9; upper nibble contains the upper digit and operates from 0 to 3. the range for the register is 1-31. battery-backed, read/write. 05h timekeeping ? day of the week d7 d6 d5 d4 d3 d2 d1 d0 0 0 0 0 0 day.2 day.1 day.0 lower nibble contains a value that correlates to day of the week. day of the week is a ring counter that counts from 1 to 7 then returns to 1. the user must assign meaning to the day value, as the day is not integrated with the date. battery-backed, read/write. 04h timekeeping ? hours d7 d6 d5 d4 d3 d2 d1 d0 0 0 10 hours.1 10 hours.0 hours.3 hours2 hours.1 hours.0 contains the bcd value of hours in 24-hour format. lower nibble contains the lower digit and operates from 0 to 9; upper nibble (two bits) contains the upper digit and operates from 0 to 2. the range for the register is 0-23. battery-backed, read/write. 03h timekeeping ? minutes d7 d6 d5 d4 d3 d2 d1 d0 0 10 min.2 10 min.1 10 min.0 min.3 min.2 min.1 min.0 contains the bcd value of minutes. lower nibble contains the lower digit and operates from 0 to 9; upper nibble contains the upper minutes digit and operates from 0 to 5. the range for the register is 0-59. battery-backed, read/write. 02h timekeeping ? seconds d7 d6 d5 d4 d3 d2 d1 d0 0 10 sec.2 10 sec.1 10 sec.0 seconds.3 seconds.2 seconds.1 seconds.0 contains the bcd value of seconds. lower nibble contains the lower digit and operates from 0 to 9; upper nibble contains the upper digit and operates from 0 to 5. the range for the register is 0-59. battery-backed, read/write.
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 14 of 25 01h cal/control d7 d6 d5 d4 d3 d2 d1 d0 oscen reserved cals cal.4 cal.3 cal.2 cal.1 cal.0 /oscen /oscillator enable. when set to 1, the oscillator is halted. when set to 0, the oscillator runs. disabling the oscillator can save battery power during storage. on a power-up without battery, this bit is set to 1. battery- backed, read/write. reserved reserved bits. do not use. should remain set to 0. cals calibration sign. determines if the calibration adjustment is applied as an addition to or as a subtraction from the time-base. calibration is explained on page 7. nonvolatile, read/write. cal.4-0 these five bits control the calibration of the clock. nonvolatile, read/write. 00h flags/control d7 d6 d5 d4 d3 d2 d1 d0 reserved cf reserved reserved reserved cal w r cf century overflow flag. this bit is set to a 1 when the values in the years register overflows from 99 to 00. this indicates a new century, such as going from 1999 to 2000 or 2099 to 2100. the user should record the new century information as needed. this bit is cleared to 0 when the flag register is read. it is read-only for the user. battery-backed. cal calibration mode. when set to 1, the clock enters calibration mode. when cal is set to 0, the clock operates normally, and the cal/pfo pin is controlled by the power fail comparator. battery-backed, read/write. w write time. setting the w bit to 1 freezes the clock. the user can then write the timekeeping registers with updated values. resetting the w bit to 0 causes the contents of the time registers to be transferred to the timekeeping counters and restarts the clock. battery-backed, read/write. r read time. setting the r bit to 1 copies a static image of the timekeeping core and place it into the user registers. the user can then read them without concerns over changing values causing system errors. the r bit going from 0 to 1 causes the timekeeping capture, so the bit must be returned to 0 prior to reading again. battery-backed, read/write. reserved reserved bits. do not use. should remain set to 0.
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 15 of 25 two-wire interface the fm31l27x employs an industry standard two- wire bus that is familiar to many users. this product is unique since it incorporates two logical devices in one chip. each logical device can be accessed individually. although monolithic, it appears to the system software to be two separate products. one is a memory device. it has a slave address (slave id = 1010b) that operates the same as a stand-alone memory device. the second device is a real-time clock and processor companion which have a unique slave address (slave id = 1101b). by convention, any device that is sending data onto the bus is the transmitter while the target device for this data is the receiver. the device that is controlling the bus is the master. the master is responsible for generating the clock signal for all operations. any device on the bus that is being controlled is a slave. the fm31l27x is always a slave device. the bus protocol is controlled by transition states in the sda and scl signals. there are four conditions: start, stop, data bit, and acknowledge. the figure below illustrates the signal conditions that specify the four states. detailed timing diagrams are shown in the electrical specifications section. stop (master) start (master) 7 data bits (transmitter) 6 0 data bit (transmitter) acknowledge (receiver) scl sda figure 9. data transfer protocol start condition a start condition is indicated when the bus master drives sda from high to low while the scl signal is high. all read and write transactions begin with a start condition. an operation in progress can be aborted by asserting a start condition at any time. aborting an operation using the start condition will ready the fm31l27x for a new operation. if the power supply drops below the specified vtp during operation, any 2-wire transaction in progress will be aborted and the system must issue a start condition prior to performing another operation. stop condition a stop condition is indicated when the bus master drives sda from low to high while the scl signal is high. all operations must end with a stop condition. if an operation is pending when a stop is asserted, the operation will be aborted. the master must have control of sda (not a memory read) in order to assert a stop condition. data/address transfer all data transfers (including addresses) take place while the scl signal is high. except under the two conditions described above, the sda signal should not change while scl is high. acknowledge the acknowledge (ack) takes place after the 8 th data bit has been transferred in any transaction. during this state the transmitter must release the sda bus to allow the receiver to drive it. the receiver drives the sda signal low to acknowledge receipt of the byte. if the receiver does not drive sda low, the condition is a no-acknowledge (nack) and the operation is aborted. the receiver might nack for two distinct reasons. first is that a byte transfer fails. in this case, the nack ends the current operation so that the part can be addressed again. this allows the last byte to be recovered in the event of a communication error. second and most common, the receiver does not send an ack to deliberately terminate an operation. for example, during a read operation, the fm31l27x will continue to place data onto the bus as long as the receiver sends acks (and clocks). when a read operation is complete and no more data is needed, the receiver must nack the last byte. if the receiver acks the last byte, this will cause the fm31l27x to attempt to drive the bus on the next clock while the master is sending a new command such as a stop.
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 16 of 25 slave address the first byte that the fm31l27x expects after a start condition is the slave address. as shown in figures below, the slave address contains the slave id, device select address, and a bit that specifies if the transaction is a read or a write. the fm31l27x has two slave addresses (slave ids) associated with two logical devices. to access the memory device, bits 7-4 should be set to 1010b. the other logical device within the fm31l27x is the real-time clock and companion. to access this device, bits 7-4 of the slave address should be set to 1101b. a bus transaction with this slave address will not affect the memory in any way. the figures below illustrate the two slave addresses. the device select bits allow multiple devices of the same type to reside on the 2-wire bus. the device select bits (bits 2-1) select one of four parts on a two- wire bus. they must match the corresponding value on the external address pins in order to select the device. bit 0 is the read/write bit. a ?1? indicates a read operation, and a ?0? indicates a write operation. 1010xa1a0r/w slave id device select 76543 21 0 figure 10. slave address - memory figure 11. slave address ? companion addressing overview ? memory after the fm31l27x acknowledges the slave address, the master can place the memory address on the bus for a write operation. the address requires two bytes. this is true for all members of the family. therefore the 4kb and 16kb configurations will be addressed differently from stand alone serial memories but the entire family will be upwardly compatible with no software changes. the first is the msb (upper byte). for a given density unused address bits are don?t cares, but should be set to 0 to maintain upward compatibility. following the msb is the lsb (lower byte) which contains the remaining eight address bits. the address is latched internally. each access causes the latched address to be incremented automatically. the current address is the value that is held in the latch, either a newly written value or the address following the last access. the current address will be held as long as vdd > vtp or until a new value is written. accesses to the clock do not affect the current memory address. reads always use the current address. a random read address can be loaded by beginning a write operation as explained below. after transmission of each data byte, just prior to the acknowledge, the fm31l27x increments the internal address. this allows the next sequential byte to be accessed with no additional addressing externally. after the last address is reached, the address latch will roll over to 0000h. there is no limit to the number of bytes that can be accessed with a single read or write operation. addressing overview ? rtc & companion the rtc and processor companion operate in a similar manner to the memory, except that it uses only one byte of address. addresses 00h to 18h correspond to special function registers. attempting to load addresses above 18h is an illegal condition; the fm31l27x will return a nack and abort the 2- wire transaction. data transfer after the address information has been transmitted, data transfer between the bus master and the fm31l27x begins. for a read, the fm31l27x will place 8 data bits on the bus then wait for an ack from the master. if the ack occurs, the fm31l27x will transfer the next byte. if the ack is not sent, the fm31l27x will end the read operation. for a write operation, the fm31l27x will accept 8 data bits from the master then send an acknowledge. all data transfer occurs msb (most significant bit) first. memory write operation all memory writes begin with a slave address, then a memory address. the bus master indicates a write operation by setting the slave address lsb to a 0. after addressing, the bus master sends each byte of data to the memory and the memory generates an acknowledge condition. any number of sequential bytes may be written. if the end of the address range is reached internally, the address counter will wrap to 0000h. internally, the actual memory write occurs after the 8 th data bit is transferred. it will be complete before the acknowledge is sent. therefore, if the 1 101x a 1 a 0r/w slave id 76543 21 0 device select
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 17 of 25 user desires to abort a write without altering the memory contents, this should be done using a start or stop condition prior to the 8 th data bit. the figures below illustrate a single- and multiple-writes to memory. figure 12. single byte memory write figure 13. multiple byte memory write memory read operation there are two types of memory read operations. they are current address read and selective address read. in a current address read, the fm31l27x uses the internal address latch to supply the address. in a selective read, the user performs a procedure to first set the address to a specific value. current address & sequential read as mentioned above the fm31l27x uses an internal latch to supply the address for a read operation. a current address read uses the existing value in the address latch as a starting place for the read operation. the system reads from the address immediately following that of the last operation. to perform a current address read, the bus master supplies a slave address with the lsb set to 1. this indicates that a read operation is requested. after receiving the complete device address, the fm31l27x will begin shifting data out from the current address on the next clock. the current address is the value held in the internal address latch. beginning with the current address, the bus master can read any number of bytes. thus, a sequential read is simply a current address read with multiple byte transfers. after each byte the internal address counter will be incremented. each time the bus master acknowledges a byte, this indicates that the fm31l27x should read out the next sequential byte. there are four ways to terminate a read operation. failing to properly terminate the read will most likely create a bus contention as the fm31l27x attempts to read out additional data onto the bus. the four valid methods follow. 1. the bus master issues a nack in the 9 th clock cycle and a stop in the 10 th clock cycle. this is illustrated in the diagrams below and is preferred. 2. the bus master issues a nack in the 9 th clock cycle and a start in the 10 th . 3. the bus master issues a stop in the 9 th clock cycle. 4. the bus master issues a start in the 9 th clock cycle. if the internal address reaches the top of memory, it will wrap around to 0000h on the next read cycle. the figures below show the proper operation for current address reads. selective (random) read there is a simple technique that allows a user to select a random address location as the starting point for a read operation. this involves using the first s a slave address 0 address msb a data byte a p by master by fm31l27x start address & data stop acknowledge address lsb a data byte a s a slave address 0 address msb a data byte a p by master by fm31l27x start a ddress & data stop a cknowledge a ddress lsb a
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 18 of 25 three bytes of a write operation to set the internal address followed by subsequent read operations. to perform a selective read, the bus master sends out the slave address with the lsb set to 0. this specifies a write operation. according to the write protocol, the bus master then sends the address bytes that are loaded into the internal address latch. after the fm31l27x acknowledges the address, the bus master issues a start condition. this simultaneously aborts the write operation and allows the read command to be issued with the slave address lsb set to a 1. the operation is now a read from the current address. read operations are illustrated below. rtc/companion write operation all rtc and companion writes operate in a similar manner to memory writes. the distinction is that a different device id is used and only one byte address is needed instead of two. figure 16 illustrates a single byte write to this device. rtc/companion read operation as with writes, a read operation begins with the slave address. to perform a register read, the bus master supplies a slave address with the lsb set to 1. this indicates that a read operation is requested. after receiving the complete slave address, the fm31l27x will begin shifting data out from the current register address on the next clock. auto- increment operates for the special function registers as with the memory address. a current address read for the registers look exactly like the memory except that the device id is different. the fm31l27x contains two separate address registers, one for the memory address and the other for the register address. this allows the contents of one address register to be modified without affecting the current address of the other register. for example, this would allow an interrupted read to the memory while still providing fast access to an rtc register. a subsequent memory read will then continue from the memory address where it previously left off, without requiring the load of a new memory address. however, a write sequence always requires an address to be supplied. figure 14. current address memory read figure 15. sequential memory read s a slave address 1 data byte 1 p by master by fm31l27x start a ddress stop a cknowledge no a cknowledge data data byte a a cknowledge s a slave address 1 data byte 1 p by master by fm31l27x start address stop acknowledge no acknowledge data
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 19 of 25 figure 16. selective (random) memory read figure 17. byte register write although not required, it is recommended that a5-a7 in the register address byte are zeros in order to preserve compatibility with future devices. addressing f-ram array in the fm31l27x family the fm31l27x family includes 256kb, 64kb, 16kb, and 4kb memory densities. the following 2-byte address field is shown for each density. table 4. two-byte memory address part # 1 s t address byte 2 n d address byte fm31l278 x a14 a13 a12 a11 a10 a9 a8 a7 a6 a5 a4 a3 a2 a1 a0 fm31l276 x x x a12 a11 a10 a9 a8 a7 a6 a5 a4 a3 a2 a1 a0 fm31l274 x x x x x a10 a9 a8 a7 a6 a5 a4 a3 a2 a1 a0 fm31l272 x x x x x x x a8 a7 a6 a5 a4 a3 a2 a1 a0 s a slave address 0 address a data byte a p by master start address & data stop acknowledge 000 by fm31l27x s a slave address 1 data byte 1 p by master by fm31l27x start address stop no acknowledge data s a slave address 0 address msb a start address acknowledge address lsb a
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 20 of 25 electrical specifications absolute maximum ratings symbol description ratings v dd power supply voltage with respect to v ss -1.0v to +5.0v v in voltage on any signal pin with respect to v ss -1.0v to +5.0v * and v in v dd +1.0v ** v bak backup supply voltage -1.0v to +4.5v t stg storage temperature -55 c to + 125 c t lead lead temperature (soldering, 10 seconds) 300 c v esd electrostatic discharge voltage - human body model (jedec std jesd22-a114-b) - charged device model (jedec std jesd22-c101-a) 3kv 1kv package moisture sensitivity level msl-1 * pfi input voltage must not exceed 4.5v. ** the ?v in < v dd +1.0v? restriction does not apply to the scl and sda inputs which do not employ a diode to v dd . stresses above those listed under absolute maximum ratings may cause permanent damage to the device. this is a stress rating on ly, and the functional operation of the device at these or any other conditions above those listed in the operational section of th is specification is not implied. exposure to absolute maximum ratings conditions for extended periods may affect device reliabilit y. dc operating conditions (t a = -40 c to + 85 c, v dd = 2.7v to 3.6v unless otherwise specified) symbol parameter min typ max units notes v dd main power supply 2.7 3.6 v 7 i dd v dd supply current @ scl = 100 khz @ scl = 400 khz @ scl = 1 mhz 500 900 1500 a a a 1 i sb standby current 120 a a 10 v tp1 v dd trip point voltage, vtp = 0 2.55 2.6 2.70 v 5 v tp2 v dd trip point voltage, vtp = 1 2.85 2.9 3.00 v 5 v rst v dd for valid /rst @ i ol = 80 1 1 ? continued ?
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 21 of 25 dc operating conditions, continued (t a = -40 c to + 85 c, v dd = 2.7v to 3.6v unless otherwise specified) symbol parameter min typ max units notes r in input resistance (pulldown) a1-a0 for v in = v il max a1-a0 for v in = v ih min 20 1 k ? m ? v pfi power fail input reference voltage 1.175 1.20 1.225 v v hys power fail input (pfi) hysteresis (rising) - 100 mv notes 1. scl toggling between v dd -0.3v and v ss , other inputs v ss or v dd -0.3v. 2. all inputs at v ss or v dd, static. stop command issued. 3. v in or v out = v ss to v dd . does not apply to a0, a1, or /rst pins. 4. v bak = 3.0v, v dd < 2.4v, oscillator running, cnt1-2 at v bak . 5. /rst is asserted low when v dd < v tp . 6. the minimum v dd to guarantee the level of /rst remains a valid v ol level. 7. full complete operation. supervisory circuits, rtc, etc operate to lower voltages as specified. 8. includes /rst input detection of external reset condition to trigger driving of /rst signal by fm31l27x. 9. the vbak trickle charger automatically regulates the maximum voltage on this pin for capacitor backup applications. 10. v bak will source current when trickle charge is enabled (vbc bit=1), v dd > v bak , and v bak < v bak max. ac parameters (t a = -40 c to + 85 c, v dd = 2.7v to 3.6v, c l = 100 pf unless otherwise specified) symbol parameter min max min max min max units notes f scl scl clock frequency 0 100 0 400 0 1000 khz t low clock low period 4.7 1.3 0.6 capacitance (t a = 25 c, f=1.0 mhz, v dd = 3.0v) symbol parameter typ max units notes c io input/output capacitance - 8 pf 1 c xtal x1, x2 crystal pin capacitance 25 - pf 1, 2 notes 1 this parameter is characterized but not tested. 2 the crystal attached to the x1/x2 pins must be rated as 12.5pf. data retention (v dd = 2.7v to 3.6v) symbol parameter min units notes t dr data retention @ +75c @ +80c @ +85c 45 20 10 years years years
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 22 of 25 supervisor timing (t a = -40 c to + 85 c, v dd = 2.7v to 3.6v) symbol parameter min max units notes t rpu /rst active (low) after v dd >v tp 100 200 ms t rnr v dd < v tp noise immunity 10 25 notes 1 this parameter is characterized but not tested. 2 slope measured at any point on v dd waveform. 3 t dog is the programmed time in register 0ah, v dd > v tp and t rpu satisfied. /rst timing vdd vtp vrst rst t rpu t rnr
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 23 of 25 ac test conditions equivalent ac load circuit input pulse levels 0.1 v dd to 0.9 v dd input rise and fall times 10 ns input and output timing levels 0.5 v dd diagram notes all start and stop timing parameters apply to both read and write cycles. clock specifications are identical for read and write cycles. write timing parameters apply to slave address, word address, and write data bits. functional relationships are illustrated in the relevant data sheet sections. these diagrams illustrate the timing parameters only. read bus timing t su:sta start t r ` t f stop start t buf t high 1/f scl t low t sp t sp acknowledge t hd:dat t su:dat t aa t dh scl sda write bus timing t su:sto start stop start acknowledge t aa t hd:dat t hd:sta t su:dat scl sda 3.6v output 1066 ? 100 pf
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 24 of 25 mechanical drawing 14-pin soic (jedec standard ms-012, variation ab) pin 1 3. 90 0.13 6.00 0. 20 8.64 0.10 0.10 0.25 1.35 1.75 0.33 0.51 1.27 0.10 mm 0. 25 0. 50 45 0. 40 1. 27 0. 19 0. 25 0 -8 recommended pcb footprint 7.70 0. 6 5 1.27 2.00 3.70 . . . . . . refer to jedec ms-012 for complete dimensions and notes. all dimensions in millimeters . soic package marking scheme legend: xxxx= part number, p= package type (-s, -g) lllllll= lot code ric=ramtron int?l corp, yy=year, ww=work week example: fm31l278, ?green?/rohs soic package, year 2007, work week 36 fm31l278-g a70023g ric 0736 xxxxxxx-p lllllll ric yyww
fm31l278/l276/l274/l272 - 3v i2c companion rev. 3.1 july 2010 page 25 of 25 revision history revision date summary 2.0 12/14/2007 initial release. 3.0 2/9/2009 changed status to production. added tape and reel ordering information. expanded data retention ratings. added ul recognition of trickle charger. 3.1 7/27/2010 removed text indicating that a manual reset sets the por flag.

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