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product preview this is a product under development. characteristic data and other ramtron international corporation specifications are design goals. ramtron reserves the right to change 1850 ramtron drive, colorado springs, co 80921 or discontinue the product without notice. (800) 545-fram, (719) 481-7000, fax (719) 481-7058 www.ramtron.com rev 0.2 sept 2001 page 1 of 18 FM30C256 256kb data collector features 256k bit ferroelectric nonvolatile ram ? organized as 32,768 x 8 bits ? high endurance 100 billion (10 11 ) read/writes ? 10 year data retention ? nodelay? writes ? advanced high-reliability ferroelectric process fast two-wire serial interface ? up to 1 mhz maximum bus frequency ? supports legacy timing for 100 khz & 400 khz ? clock registers accessed via 2-wire interface real-time clock/calendar ? backup current under 1 a ? tracks seconds through centuries (bcd format) ? tracks leap years through 2099 ? uses standard 32.768 khz crystal (6pf) ? software calibration system supervisor ? active-low reset output for v dd out-of-tolerance ? tamper detect input with battery backup and time stamp description the FM30C256 is a 256-kilobit data collection subsystem including nonvolatile ram, timekeeping, cpu supervisor, and system tamper detection. non- volatile ram is provided by fram technology, which is ideal for collection data and requires no battery backup for nonvolatile storage. in other respects, it provides the same features as sram. fram performs write operations at bus speed with no write delays. write cycles can be continuous without block limitations. in addition, it offers much higher write endurance than other nonvolatile memories. the FM30C256 supports up to 10 11 read/write cycles. the FM30C256 also includes timekeeping with external battery backup. the timekeeper consists of registers that represent time and date information in bcd format. the clock includes a calibration mode that allows a software adjustment for timekeeping accuracy. to maintain system data integrity, the FM30C256 provides a reset signal asserted when vdd is out of tolerance. /rst remains active for 100 ms after vdd returns to proper levels. the FM30C256 also provides a battery-backed tamper detect circuit that records a rising edge on the tin input. a battery- backed flag is set when the event occurs, but can only be cleared by software. the FM30C256 is provided in a 20-pin sop package and is guaranteed over an industrial temperature range of -40c to +85c. pin configuration pin names function tin tamper detect input a0-a2 device select inputs cal clock calibration output /rst reset output x1, x2 crystal connections sda serial data scl serial clock vdd supply voltage 5v vbak battery-backup input vss ground ordering information FM30C256-s 20-pin sop vdd vbak scl sda vss x1 x2 cal tin nc nc nc nc rst nc a0 a1 a2 nc nc 1 2 3 4 5 6 7 8 9 10 20 19 18 17 16 15 14 13 12 11
FM30C256 rev 0.2 sept 2001 page 2 of 18 figure 1. block diagram pin descriptions pin name type pin description a2-a0 input device select inputs are used to address the part on a serial bus. to select the device, the address value on the three pins must match the corresponding bits contained in the device address. note that these are not address pins for read/write operations. the address pins are pulled down internally. tin input tamper detect is a battery backed input that stores a 1 in the flags/control register when it detects a rising edge on the tin pin. cal output 512 hz square-wave output for clock calibration x1, x2 i/o 32.768 khz crystal connection /rst output active low reset output (open drain) 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-ored 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 schmit trigger input for noise immunity. vbak supply battery backup supply voltage (3v) vdd supply supply voltage (5v) vss supply ground nc - no connect address latch & counter 8,192 x 32 fram array rtc address latch & counter serial to parallel converter data latch 8 protocol & device select real-time clock registers power isolation tamper flag counters power management rtc oscillator tamper latch battery-backed power cal tin x2 x1 rst vbak vdd scl sda a2-a0
FM30C256 rev 0.2 sept 2001 page 3 of 18 overview the FM30C256 data collector combines a 256kb serial nonvolatile ram with a real-time clock (rtc), a power monitor, and a tamper detect circuit. the FM30C256 integrates these complementary but distinct functions under a common interface in a single package. despite providing multiple interface ids as explained below, the product is a single monolithic device. the memory is organized as 32kx8 of fram and is accessed via a separate 2-wire device id from the remaining functions. this allows the user to preserve addressing information when switching between memory and rtc functions. modularity in software design is preserved as well. the real-time clock function and the tamper detection is accessed under its own 2-wire device id. this allows clock data to be read while maintaining the last (most recently used) memory address in the other device. the clock and tamper functions are controlled by 9 registers that are backed up by the external battery. clock and tamper functions continue to operate from battery power when v dd drops below the battery voltage. in addition to the software-controlled functions, the FM30C256 also provides reset signal for an external microcontroller host. this signal is asserted when v dd drops below the specified trip point (v tp ). it remains asserted until v dd returns above v tp for the hold-off period (t rpu ). the power monitor has no interaction with other software-controlled functions. any access to the device will be ignored when v dd < v tp . memory operation when accessing the FM30C256, the user addresses 32,768 locations each with 8 data bits. these data bits are shifted in and out serially. the 32,768 addresses are accessed using the two-wire protocol, which includes a slave address (to distinguish from other non-memory devices), and an extended 16-bit address. the decoder uses only the lower 15 bits for accessing the memory. the upper address bit should be set to 0 for compatibility with larger devices in the future. the memory is read or written at the speed of the two-wire bus. the interface protocol is described further below. rtc register map the interface to clock and tamper functions is via 9 address locations 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 short description of each register follows. detailed descriptions follow the register summary section. register map summary table data address d7 d6 d5 d4 d3 d2 d1 d0 function range 9-f 8 10 years years years 00-99 7 00010 mo months month 1-12 6 00 10 date date date 1-31 5 00000 day da y 1-7 4 00 10 hours hours hours 0-23 3 0 10 minutes minutes minutes 0-59 2 0 10 seconds seconds seconds 0-59 1 /oscen tsen cals cal4 cal3 cal2 cal1 cal0 cal/control 0 tamper cf reserved reserved tst cal w r fla g s/control illegal addresses
FM30C256 rev 0.2 sept 2001 page 4 of 18 table 1. register map address description 8h 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. 7h 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. 6h 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. 5h 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. 4h 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. 3h 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. 2h 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.
FM30C256 rev 0.2 sept 2001 page 5 of 18 address description 1h cal/control d7 d6 d5 d4 d3 d2 d1 d0 oscen tsen 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. tsen time stamp enable. when set to 1, a tamper detect event will record the date and time of the event. on a power-up without battery, this bit is 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 below. cal.4-0 these five bits control the calibration of the clock. 0h flags/control d7 d6 d5 d4 d3 d2 d1 d0 tamper cf reserved reserved tst cal w r tamper tamper detect. this bit is set to 1 when rising edge is detected on the tin pin. it can only be cleared to 0 by the user. 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. tst invokes factory test mode. users should always set this bit to 0. 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 pin is driven low. w write time. setting the w bit to 1 freezes updates of the timekeeping registers. the user can then write them with updated values. setting the w bit to 0 causes the contents of the time registers to be transferred to the timekeeping counters. r read time. setting the r bit to 1 copies a static image of the timekeeping registers and places them in a holding register. 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. reserved reserved bits. do not use. should remain set to 0. real-time clock operation the real-time clock (rtc) consists of an oscillator, divider, and a register system for accessing the information. it divides down the 32.768 khz time- base and provides a minimum resolution of seconds (1hz) to the user. static registers provide the user with read/write access to the time values. the synchronization of these registers with the timekeeper core is performed using r and w bits in register 0. changing the r bit from 0 to 1 causes a transfer of the timekeeping information to holding registers that can be read by the user. if a timekeeper update is pending when r is set, then the update will be completed prior to loading the registers. another update cannot be performed until the r bit is cleared to 0. setting the w bit to 1 causes the timekeeper to freeze updates. clearing it to 0 causes the values in the time registers to be written into the timekeeper core. 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 frozen. a diagram of the timekeeping core follows. backup power the real-time clock/calendar is intended for permanently powered operation. when the primary system power fails, the voltage on the vdd pin will drop. when vdd is less than the voltage on the vbak pin, the clock will switch to the backup power supply. the clock operates at extremely low current in order to maximize battery life. however, an advantage of combining a clock function with fram is that the 256k memory data is not lost regardless of the backup power source.
FM30C256 rev 0.2 sept 2001 page 6 of 18 32.768 khz crystal oscillator clock divider 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 figure 2. real-time clock core block diagram calibration when the cal bit in register 0 is set to 1, the clock enters calibration mode. calibration operates by applying a digital correction to the counter based on the frequency error. in cal mode, the cal pin is driven with a 512 hz (nominal) square wave. any measured deviation from 512 hz is converted to an error in ppm. this error corresponds to a correction value that is then written by the user into 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 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 battery backed and is stored in bits cal.4-0. this value only can be written when the cal bit is set to a 1. to exit the calibration mode, the user should clear the cal bit to a 0. when the cal bit is 0, the cal pin will be driven low. when the calibration mode is entered, the user can measure the frequency error on the cal pin. this error expressed in ppm translates directly into timekeeping error. an offsetting calibration adjustment corrects this error. however, the correction is applied by adding or removing pulses on a periodic basis. therefore, the correction will not appear on the 512 hz output. the calibration correction must be applied using the lookup table below. the timekeeping accuracy can be verified by comparing the FM30C256 time to a reference source.
FM30C256 rev 0.2 sept 2001 page 7 of 18 table 2. calibration adjustments 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 1 10000 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 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 positive calibration for slow clocks: calibration will achieve +/- 2.17 ppm after calibration ne g ative calibration for fast clocks: calibration will achieve +/- 2.17 ppm after calibration
FM30C256 rev 0.2 sept 2001 page 8 of 18 tamper detection and time stamp the tin pin is a battery backed input that is used to detect a tamper event in the system. when a rising edge occurs on tin, this tamper detect event is recorded in the msb of register 0. this action will occur only when either v bak or v dd is applied. any further activity on tin, such as a falling edge, will be ignored. the user is responsible for reading and clearing the tamper flag. clearing the tamper flag allows the tin to detect another rising edge. the tamper flag can only be read or cleared when v dd 4.5v. on a power-up without battery, this bit is set to zero. the tamper input tin can be used to timestamp the exact time a tamper event occurred. this feature can be enabled by setting the timestamp enable bit tsen in the calibration control register (rtc address 1, bit d6). at power-up, tsen is cleared and must be set by the user. when a rising edge occurs on tin and the tsen bit is set, the date and time of the event will be recorded. the current time is loaded into the timekeeping registers. when the system is checked for a tamper event, the time of the event can be read. after a tamper event, the timekeeping registers can be overwritten if the r bit is set before reading the timekeeping registers. to prevent overwriting the timestamp, the control register should be read first to check that the tamper bit is set. if it is set, the timekeeping registers should be read to collect the time of the last tamper event. checking for a tamper event before setting the r bit will ensure accurate tamper timestamp information. if the tsen bit is not set, then a rising edge on tin will not trigger a timestamp. system reset control the /rst pin allows the user to easily control a system level reset function. it is an open drain output and requires an external pullup resistor to v dd for proper operation. when v dd is within the specified operating range, /rst is tri-stated and pulled to v dd by the external resistor. if v dd drops below the reset trip point voltage level (v tp ) and remains below this level for the v tp noise immunity duration (t rnr ), the /rst pin will be driven low. it will continue to drive low until v dd falls below the v rst level. when v dd rises again above v tp , /rst will continue to drive low for a duration (t rpu ) to ensure a robust system reset at a reliable v dd level. after t rpu has been met, the /rst pin tri-states and is pulled high by the external pullup resistor. refer to the figure on page 16 for a graphical description of the /rst function and timing. 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
FM30C256 rev 0.2 sept 2001 page 9 of 18 two-wire interface the FM30C256 employs an industry standard two- wire bus that is familiar to many users and for convenience is described in this section. the FM30C256 is unique since it incorporates two logical devices in one chip. each logical device can be accessed individually. 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 tamper detect which share 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 FM30C256 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. figure 4 illustrates the signal conditions that specify the four states. detailed timing diagrams are shown in the electrical specifications. 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 FM30C256 for a new operation. if the power supply drops below the specified vdd minimum during operation, the system should 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 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 and the operation is aborted. the receiver would fail to acknowledge for two distinct reasons. first is that a byte transfer fails. in this case, the no-acknowledge 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 acknowledge to deliberately end an operation. for example, during a read operation, the FM30C256 will continue to place data onto the bus as long as the receiver sends acknowledges (and clocks). when a read operation is complete and no more data is needed, the receiver must not acknowledge the last byte. if the receiver acknowledges the last byte, this will cause the FM30C256 to attempt to drive the bus on the next clock while the master is sending a new command such as a stop. stop (master) start (master) 7 data bits (transmitter) 6 0 data bit (transmitter) acknowledge (receiver) scl sda figure 3. data transfer protocol
FM30C256 rev 0.2 sept 2001 page 10 of 17 slave address the first byte that the FM30C256 expects after a start condition is the slave address. as shown in figure 4, 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 FM30C256 has two slave addresses (slave ids) associated with two logical devices. to access the memory device, bits 7-4 should be set to 1010b. see figure 4. the other logical device within the FM30C256 is the real-time clock and tamper detect. 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. see figure 5. the slave id bits allow other function types to reside on the 2-wire bus for a given device select address. the device select bits (bits 3-1) are used to select one of eight chips on a two-wire bus. they must match the corresponding value on the external address pins in order to select the device. up to eight devices can reside on the same two-wire bus by assigning a different address to each device. bit 0 is the read/write bit. a ?1? indicates a read operation, and a ?0? indicates a write operation. 1010 r/w slave id 7654321 0 device select a2 a1 a0 figure 4. slave address - memory 1101 r/w slave id 7654321 0 device select a2 a1 a0 figure 5. slave address - rtc addressing overview - memory after the FM30C256 acknowledges the slave address, the master can place the memory address on the bus for a write operation. the address requires two bytes. the first is the msb (upper byte). since the device uses only 15 address bits, the value of the upper bit is a ?don?t care?. 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 power remains 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 FM30C256 increments the internal address. this allows the next sequential byte to be accessed with no additional addressing externally. after the last address (7fffh) 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 the rtc operates in a similar manner to the memory, except that it uses only one byte of address. the low four bits of address specify register 0-8, and the upper four bits are ?don?t care?. only addresses 0 through 8 should be loaded during an rtc write command. loading addresses 9-f is an illegal condition and should not be attempted since unpredictable results could occur. data transfer after the address information has been transmitted, data transfer between the bus master and the FM30C256 begins. for a read, the FM30C256 will place 8 data bits on the bus then wait for an acknowledge from the master. if the acknowledge occurs, the FM30C256 will transfer the next byte. if the acknowledge is not sent, the FM30C256 will end the read operation. for a write operation, the FM30C256 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 from 7fffh 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 user desires to abort a write without
FM30C256 rev 0.2 sept 2001 page 11 of 18 altering the memory contents, this should be done using a start or stop condition prior to the 8 th data bit. figures 6 and 7 illustrate a single- and multiple- writes to memory. s a slave address 0 address msb a data byte a p by master by FM30C256 start address & data stop acknowledge address lsb a figure 6. single byte memory write s a slave address 0 address msb a data byte a p by master by FM30C256 start address & data stop acknowledge address lsb a data byte a figure 7. 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 FM30C256 uses the internal address latch to supply the address. in a selective read, the user performs a procedure to set the address to a specific value. current address & sequential read as mentioned above the FM30C256 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 FM30C256 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 FM30C256 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 FM30C256 attempts to read out additional data onto the bus. the four valid methods follow. 1. the bus master issues a no-acknowledge in the 9 th clock cycle and a stop in the 10 th clock cycle. this is illustrated in the diagrams below. this is preferred. 2. the bus master issues a no-acknowledge 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 7fffh, it will wrap around to 0000h on the next read cycle. figures 8 and 9 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 three bytes of a write operation to set the internal address followed by subsequent read operations.
FM30C256 rev 0.2 sept 2001 page 12 of 18 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 FM30C256 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. figure 10 shows the proper operation for a selective read. rtc write operation all rtc 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 11 illustrates a single byte write to the clock. rtc 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 FM30C256 will begin shifting data out from the current register address on the next clock. auto- increment operates for the rtc address as with the memory address. a current address read for the rtc looks exactly like the memory except that the device id is different. the FM30C256 contains two separate address registers, one for the 256k memory address and the other for the rtc 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. s a slave address 1 data byte 1 p by master by FM30C256 start address stop acknowledge no acknowledge data figure 8. current address memory read s a slave address 1 data byte 1 p by master by FM30C256 start address stop acknowledge no acknowledge data data byte a acknowledge figure 9. sequential memory read
FM30C256 rev 0.2 sept 2001 page 13 of 18 s a slave address 1 data byte 1 p by master by FM30C256 start address stop no acknowledge data s a slave address 0 address msb a start address acknowledge address lsb a figure 10. selective (random) memory read s a slave address 0 address a data byte a p by master by FM30C256 start address & data stop acknowledge xx x x figure 11. byte rtc write
FM30C256 rev 0.2 sept 2001 page 14 of 18 electrical specifications absolute maximum ratings symbol description ratings v dd power supply voltage with respect to v ss -1.0v to +7.0v v in voltage on any signal pin with respect to v ss -1.0v to +7.0v and v in < v dd +1.0v t stg storage temperature -40 c to + 85 c t lead lead temperature (soldering, 10 seconds) 300 c stresses above those listed under absolute maximum ratings may cause permanent damage to the device. this is a stress rating only, and the functional operation of the device at these or any other conditions above those listed in the operational section of this specification is not implied. exposure to absolute maximum ratings conditions for extended periods may affect device reliability. dc operating conditions (t a = -40 c to + 85 c, v dd = 4.5v to 5.5v unless otherwise specified) symbol parameter min typ max units notes v dd main power supply 4.5 5.0 5.5 v i dd v dd supply current @ scl = 100 khz @ scl = 400 khz @ scl = 1 mhz 300 650 1.35 a a ma 1 i sb standby current 150 a 2 v bak clock backup voltage 2.5 3.0 3.5 v i bak clock backup current 1 a 5 v tp reset trip point 4.2 4.45 v 6 v rst v dd min for active /rst @ i ol = 10 a, v ol = 0.4v 1.2 - v 7 i li input leakage current 10 a 3 i lo output leakage current 10 a 3 v il input low voltage -0.3 0.3 v dd v v ih input high voltage 0.7 v dd v dd + 0.5 v v ilb input low voltage (tin) for v dd < v bak -0.3 0.5 v 4 v ihb input high voltage (tin) for v dd < v bak v bak - 0.5 v bak + 0.5 v 4 v ol output low voltage (cal, /rst, sda) @ i ol = 3 ma 0.4 v v oh output high voltage (cal) @ i oh = -2 ma 2.4 v r in address input resistance (a2-a0) for v in = v il (max) for v in = v ih (min) 2 0 1 k ? m ? v hys input hysteresis 0.05 v dd v 4 notes 1. scl toggling between v dd -0.3v and v ss , other inputs v ss or v dd -0.3v 2. scl = sda = v dd . all inputs v ss or v dd . stop command issued. 3. v in or v out = v ss to v dd . does not apply to pins with internal pull down resistors. 4. this parameter is characterized but not tested. 5. v bak = 3.0v, v dd < v bak ; oscillator running. 6. /rst is asserted active when v dd < v tp . 7. the minimum v dd to guarantee the level of /rst remains a valid v ol level.
FM30C256 rev 0.2 sept 2001 page 15 of 18 ac parameters (t a = -40 c to + 85 c, v dd = 4.5v to 5.5v, 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 s t high clock high period 4.0 0.6 0.4 s t aa scl low to sda data out valid 3 0.9 0.55 s t buf bus free before new transmission 4.7 1.3 0.5 s t hd:sta start condition hold time 4.0 0.6 0.25 s t su:sta start condition setup for repeated start 4.7 0.6 0.25 s t hd:dat data in hold 0 0 0 ns t su:dat data in setup 250 100 100 ns t r input rise time 1000 300 300 ns 1 t f input fall time 300 300 100 ns 1 t su:sto stop condition setup 4.0 0.6 0.25 s t dh data output hold (from scl @ vil) 0 0 0 ns t sp noise suppression time constant on scl, sda 50 50 50 ns notes: all scl specifications as well as start and stop conditions apply to both read and write operations. 1 this parameter is periodically sampled and not 100% tested. power cycle timing (t a = -40 c to + 85 c) symbol parameter min typ max units notes t rpu reset active after v dd >v tp 100 - 200 ms t rnr v dd < v tp noise immunity 10 - 25 s 1 t r rise time of v dd from v bak to v tp 100 - s 1,2 t f fall time of v dd from v tp to v bak 100 - s 1,2 notes 1 this parameter is periodically sampled and not 100% tested. 2 slew rate for proper transition between the battery-backed and normal operation. data retention (v dd = 4.5v to 5.5v unless otherwise specified) parameter min units notes data retention 10 years 1 notes 1. the relationship between retention, temperature, and the associated reliability level is characterized separately. capacitance (t a = 25 c, f=1.0 mhz, v dd = 5v) symbol parameter max units notes c io input/output capacitance (sda) 8 pf 1 c i input capacitance 6 pf 1 c xtal x1, x2 crystal pin capacitance 12 pf 1, 2 notes 1 this parameter is periodically sampled and not 100% tested. 2 the crystal attached to the x1/x2 pins must be rated as 6pf.
FM30C256 rev 0.2 sept 2001 page 16 of 18 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:sda start t r ` t f stop start t buf t high 1/fscl t low t sp t sp acknowledge t hd:dat t su:d at 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 /rst timing vdd vtp vrst rst t rpu vbak t f t r t rnr 5.5v output 1700 ? 100 pf
FM30C256 rev 0.2 sept 2001 page 17 of 18 20-pin sop (jedec standard ms-013 variation ac) pin 1 index area e h d a1 a b e 0.10 mm 0.004 in. h 45 l c controlling dimensions in millimeters. conversions to inches are not necessarily exact. symbol dim min nom. max a mm in. 2.35 0.093 2.65 0.104 a1 mm in. 0.10 0.004 0.30 0.012 b mm in. 0.33 0.013 0.51 0.020 c mm in. 0.23 0.009 0.32 0.013 d mm in. 12.60 0.496 13.00 0.512 e mm in. 7.40 0.291 7.50 0.295 7.60 0.299 e mm in. 1.27 bsc 0.050 bsc h mm in. 10.00 0.393 10.65 0.419 l mm in. 0.40 0.016 1.27 0.05 0 8
FM30C256 rev 0.2 sept 2001 page 18 of 18 revision history revision date summary 0.1 5/10/01 initial release 0.2 9/17/01 updated package & pinout. changed idd and capacitance specifications. cal pin changed from open drain to push/pull. cal pin drives low when cal bit is reset. tin pin powered by vbak, added dc specs for tin. timestamp feature added to tamper detect. changed test load to 1700 ohms to reflect 3ma v ol test condition.

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