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general description the ds1388 i 2 c real-time clock (rtc), supervisor, and eeprom is a multifunction device that provides a clock/calendar, programmable watchdog timer, power- supply monitor with reset, and 512 bytes of eeprom. the clock provides hundredths of seconds, seconds, minutes, and hours, and operates in 24-hour or 12-hour format with an am/pm indicator. the calendar provides day, date, month, and year information. the date at the end of the month is automatically adjusted for months with fewer than 31 days, including corrections for leap year. a watchdog timer provides a reset for an unre- sponsive microprocessor. it is programmable in 10ms intervals from 0.01 to 99.99 seconds. a temperature- compensated voltage reference and comparator circuit monitors the status of v cc . if a primary power failure is detected, the device automatically switches to the backup supply and drives the reset output to the active state. the backup supply maintains time and date operation in the absence of v cc . when v cc returns to nominal levels, the reset is held low for a period to allow the power supply and processor to stabilize. the device also has a pushbutton reset controller, which debounces a reset input signal. the device is accessed through an i 2 c serial interface. applications portable instruments point-of-sale equipment network interface cards wireless equipment features ? fast (400khz) i 2 c interface ? rtc counts hundredths of seconds, seconds, minutes, hours, day, date, month, and year with leap year compensation valid up to 2100 ? programmable watchdog timer ? automatic power-fail detect and switch circuitry ? reset output with pushbutton reset input capability ? 512 x 8 bits of eeprom ? integrated trickle-charge capability for backup supply ? three operating voltages: 5.0v, 3.3v, and 3.0v ? low timekeeping voltage down to 1.3v ? -40? to +85? temperature range ? ul recognized ds1388 i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom ______________________________________________ maxim integrated products 1 1 2 3 4 8 7 6 5 v cc rst scl sda v backup gnd x2 x1 top view ds1388 so pin configuration rst v cc x1 scl x2 cpu v cc ds1388 sda gnd v cc rpu rpu = t r /c b rpu v cc crystal v backup t ypical operating circuit rev 0; 4/05 for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. a ??symbol near the pin one indicator indicates lead-free. + = lead free. ordering information part temp range pin- package top mark ds1388z-3 -40? to +85? 8 so (150 mils) ds1388-3 ds1388z-33 -40? to +85? 8 so (150 mils) ds138833 ds1388z-5 -40? to +85? 8 so (150 mils) ds1388-5 ds1388z-5+ -40? to +85? 8 so (150 mils) ds1388-5 ds1388z-33+ -40? to +85? 8 so (150 mils) ds138833 ds1388z-3+ -40? to +85? 8 so (150 mils) ds1388-3 purchase of i 2 c components from maxim integrated products, inc., or one of its sublicensed associated companies, conveys a license under the philips i 2 c patent rights to use these com- ponents in an i 2 c system, provided that the system conforms to the i 2 c standard specification as defined by philips.
ds1388 i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom 2 _____________________________________________________________________ absolute maximum ratings recommended dc operating conditions (t a = -40? to +85?, unless otherwise noted.) (note 1) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. voltage range on v cc pin relative to ground .....-0.3v to +6.0v voltage range on inputs relative to ground ...............................................-0.3v to (v cc + 0.3v) operating temperature range (noncondensing) .............................................-40? to +85? storage temperature range .............................-55? to +125? soldering temperature .....................see ipc/jedec j-std-020 specification parameter symbol conditions min typ max units ds1388z-5 4.5 5 5.5 ds1388z-33 2.97 3.3 3.63 supply voltage v cc (note 2) ds1388z-3 2.7 3 3.3 v logic 1 v ih (note 2) 0.7 x v cc v cc + 0.3 v logic 0 v il (note 2) -0.3 +0.3 x v cc v pullup voltage (scl, sda), v cc = 0v v pu 5.5 v v backup voltage v backup (note 2) 1.3 3.0 5.5 v ds1388z-5 4.15 4.33 4.50 ds1388z-33 2.70 2.88 2.97 power-fail voltage v pf (note 2) ds1388z-3 2.45 2.60 2.70 v dc electrical characteristics ( v cc = v cc(min) to v cc(max) , t a = -40? to +85?, unless otherwise noted.) (note 1) parameter symbol conditions min typ max units r1 (notes 3, 4) 250 r2 (note 5) 2000 trickle-charger current-limiting resistors r3 (note 6) 4000 ? input leakage (scl) i li -1 +1 ? i/o leakage (sda) i lo -1 +1 ? i/o leakage ( rst )i lorst (note 7) -200 +10 ? sda logic 0 output (v ol = 0.15 x v cc ) i oldout 3ma
ds1388 i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom _____________________________________________________________________ 3 dc electrical characteristics (continued) ( v cc = v cc(min) to v cc(max) , t a = -40? to +85?, unless otherwise noted.) (note 1) parameter symbol conditions min typ max units v cc > 2v; v ol = 0.4v 3.0 1.8v < v cc < 2v; v ol = 0.2 x v cc 3.0 ma rst logic 0 output i olsir 1.3v < v cc < 1.8v; v ol = 0.2 x v cc 250 ? ds1388z-5 600 ds1388z-33 250 v cc active current, eeprom read, i 2 c read/write access i ccer (note 8) ds1388z-3 225 ? ds1388z-5 1.0 ds1388z-33 0.70 v cc active current, eeprom write cycle i ccew (note 8) ds1388z-3 0.65 ma ds1388z-5 270 ds1388z-33 100 150 v cc standby current i ccs (note 9) ds1388z-3 140 ? v backup leakage current (v backup = 3.7v, v cc = v cc(max) ) i backuplkg 15 100 na t a = +25? (guaranteed by design) 200k eeprom write/erase cycles t wr t a = -40? to +85? (guaranteed by design) 50k cycles dc electrical characteristics ( v cc = 0v, v backup = 3.7v , t a = +25?, unless otherwise noted.) (note 1) parameter symbol conditions min typ max units v backup current, osc on ( eosc = 0), sda = scl = 0v i backup (note 10) 410 550 na v backup current, osc off ( eosc = 1), sda = scl = 0v (data retention) i backupdr (note 10) 10 100 na
ds1388 i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom 4 _____________________________________________________________________ ac electrical characteristics (v cc = v cc(min) to v cc(max) , t a = -40? to +85?, unless otherwise noted.) (note 1) parameter symbol condition min typ max units fast mode 100 400 scl clock frequency f scl standard mode 0 100 khz fast mode 1.3 bus free time between a stop and start condition t buf standard mode 4.7 ? fast mode 0.6 hold time (repeated) start condition (note 11) t hd:sta standard mode 4.0 ? fast mode 1.3 low period of scl clock t low standard mode 4.7 ? fast mode 0.6 high period of scl clock t high standard mode 4.0 ? fast mode 0.6 setup time for a repeated start condition t su:sta standard mode 4.7 ? fast mode 0 0.9 data hold time (notes 12, 13) t hd:dat standard mode 0 ? fast mode 100 data setup time (note 14) t su:dat standard mode 250 ns fast mode 300 rise time of both sda and scl signals (note 15) t r standard mode 20 + 0.1c b 1000 ns fast mode 300 fall time of both sda and scl signals (note 15) t f standard mode 20 + 0.1c b 300 ns fast mode 0.6 setup time for stop condition t su:sto standard mode 4.0 ? capacitive load for each bus line (note 15) c b 400 pf i/o capacitance (sda, scl, rst ) c i/o +25? 10 pf pushbutton debounce pb db 160 180 ms reset active time t rst 160 180 ms eeprom write cycle time t wee 810ms oscillator stop flag (osf) delay (note 16) t osf 20 ms
ds1388 i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom _____________________________________________________________________ 5 power-up/power-down characteristics (t a = -40? to +85?) (note 1) (figures 1, 2) parameter symbol conditions min typ max units v cc detect to recognize inputs (v cc rising) t rst (note 17) 160 180 ms v cc fall time; v pf(max) to v pf(min) t f 300 ? v cc rise time; v pf(min) to v pf(max) t r 0s outputs v cc v pf(max) inputs high impedance rst don't care v alid recognized recognized v alid v pf(min) t rst t rpu t r t f v pf v pf figure 1. power-up/down timing t rst pb db rst figure 2. pushbutton reset timing
ds1388 i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom 6 _____________________________________________________________________ w arning: under no circumstances are negative undershoots, of any amplitude, allowed when device is in write protection. note 1: limits at -40? are guaranteed by design and are not production tested. note 2: all voltages are referenced to ground. note 3: measured at v cc = typ, v backup = 0v, register 0ah, block 0h = a5h. note 4: the use of the 250 ? trickle-charge resistor is not allowed at v cc > 3.63v and should not be enabled. note 5: measured at v cc = typ, v backup = 0v, register 0ah, block 0h = a6h. note 6: measured at v cc = typ, v backup = 0v, register 0ah, block 0h = a7h. note 7: the rst pin has an internal 50k ? pullup resistor to v cc . note 8: i cca ?cl clocking at max frequency = 400khz. note 9: specified with i 2 c bus inactive. note 10: measured with a 32.768khz crystal attached to x1 and x2. note 11: after this period, the first clock pulse is generated. note 12: a device must internally provide a hold time of at least 300ns for the sda signal (referred to the v ihmin of the scl signal) to bridge the undefined region of the falling edge of scl. note 13: the maximum t hd:dat need only be met if the device does not stretch the low period (t low ) of the scl signal. note 14: a fast-mode device can be used in a standard-mode system, but the requirement t su:dat 250ns must then be met. this is automatically the case if the device does not stretch the low period of the scl signal. if such a device does stretch the low period of the scl signal, it must output the next data bit to the sda line t r(max) + t su:dat = 1000 + 250 = 1250ns before the scl line is released. note 15: c b ?otal capacitance of one bus line in pf. note 16: the parameter t osf is the period of time that the oscillator must be stopped for the osf flag to be set over the voltage range of 0v v cc v cc(max) and 1.3v v backup 3.7v. note 17: if the oscillator is disabled or stopped, rst goes inactive after t rst plus the startup time of the oscillator.
ds1388 i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom _____________________________________________________________________ 7 v cc falling vs. rst delay ds1388 toc04 v cc falling (v/ms) reset delay ( s) 10 1 0.1 100 1000 10,000 10 0.01 100 v cc = v pf + 0.1v to 0v i backup supply current voltage vs. temperature ds1388 toc02 temperature ( c) supply current (na) 65 50 35 20 5 10 -25 300 350 400 450 500 550 600 250 -40 80 v backup = 3v oscillator frequency vs. supply voltage ds1388 toc03 supply (v) frequency (hz) 5.3 4.8 3.8 4.3 2.3 2.8 3.3 1.8 32768.05 32768.10 32768.15 32768.20 32768.25 32768.30 32768.35 32768.40 32768.45 32768.00 1.3 i backup supply current voltage vs. v backup ds1388 toc01 v backup (v) supply current (na) 5.3 4.9 4.5 4.1 3.7 3.3 2.9 2.5 2.1 1.7 300 350 400 450 500 250 1.3 v cc = 0v t ypical operating characteristics (v cc = +3.3v, t a = +25?, unless otherwise noted.)
ds1388 i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom 8 _____________________________________________________________________ pin description block diagram pin name function 1x1 2x1 connections for a standard 32.768khz quartz crystal. the internal oscillator circuitry is designed for operation with a crystal having a specified load capacitance (c l ) of 6.0pf. pin x1 is the input to the oscillator and can optionally be connected to an external 32.768khz oscillator. the output of the internal oscillator, pin x2, is floated if an external oscillator is connected to pin x1. 3 v backup connection for a secondary power supply. supply voltage must be held between 1.3v and 5.5v for proper operation. this pin can be connected to a primary cell, such as a lithium button cell. additionally, this pin can be connected to a rechargeable cell or a super cap when used with the trickle-charge feature. if not used, this pin must be connected to ground. ul recognized to ensure against reverse charging current when used with a lithium battery. ( www.maxim-ic.com/qa/info/ul/ ) 4 gnd ground 5 sda serial data output. sda is the input/output for the i 2 c serial interface. this pin is open drain and requires an external pullup resistor. 6 scl serial clock input. scl is the clock input for the i 2 c interface and is used to synchronize data movement on the serial interface. 7 rst active-low, open-drain reset output. this pin indicates the status of v cc relative to the v pf specification. as v cc falls below v pf , the rst pin is driven low. when v cc exceeds v pf , for t rst , the rst pin is driven high impedance. the active-low, open-drain output is combined with a debounced pushbutton input function. this pin can be activated by a pushbutton reset request. it has an internal 50k ? nominal value pullup resistor to v cc . no external pullup resistors should be connected. if the crystal oscillator is disabled, the startup time of the oscillator is added to the t rst delay. 8v cc dc power pin for primary power supply x1 x2 v cc gnd v backup rst sda scl block 2 block 1 block 0 rtc oscillator/ clock divider power control and trickle charger i 2 c interface eeprom interface eeprom eeprom wa tchdog timer stat/ctrl/trickle ds1388
ds1388 i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom _____________________________________________________________________ 9 detailed description the ds1388 i 2 c rtc, supervisor, and eeprom is a multifunction device that provides a clock/calendar, programmable watchdog timer, power-supply monitor with reset, and 512 bytes of eeprom. the clock pro- vides hundredths of seconds, seconds, minutes, and hours, and operates in 24-hour or 12-hour format with an am/pm indicator. the calendar provides day, date, month, and year information. the date at the end of the month is automatically adjusted for months with fewer than 31 days, including corrections for leap year. a watchdog timer provides a reset for an unresponsive microprocessor. it is programmable in 10ms intervals from 0.01 to 99.99 seconds. a temperature-compensat- ed voltage reference and comparator circuit monitors the status of v cc . if a primary power failure is detected, the device automatically switches to the backup supply and drives the reset output to the active state. when v cc returns to nominal levels, the reset is held low for a period to allow the power supply and processor to sta- bilize. the device also has a pushbutton reset con- troller, which debounces a reset input signal. the device is accessed through an i 2 c serial interface. operation the ds1388 operates as a slave device on the i 2 c bus. access is obtained by implementing a start condition and providing a device identification code followed by data. subsequent registers can be accessed sequen- tially until a stop condition is executed. see the block diagram , which shows the main elements of the serial real-time clock. power control the power-control function is provided by a precise, temperature-compensated voltage reference and a comparator circuit that monitors the v cc level. the device is fully accessible and data can be written and read when v cc is greater than v pf . however, when v cc falls below v pf , the internal clock registers are blocked from any access. if v pf is less than v backup , the device power is switched from v cc to v backup when v cc drops below v pf . if v pf is greater than v backup , the device power is switched from v cc to v backup when v cc drops below v backup . the regis- ters are maintained from the v backup source until v cc is returned to nominal levels (table 1). after v cc returns above v pf , read and write access is allowed after rst goes high (figure 1). oscillator circuit the ds1388 uses an external 32.768khz crystal. the oscillator circuit does not require any external resistors or capacitors to operate. table 2 specifies several crystal parameters for the external crystal, and figure 3 shows a functional schematic of the oscillator circuit. using a crystal with the specified characteristics, the startup time is usually less than one second. supply condition read/write access powered by v cc < v pf , v cc < v backpup no v backup v cc < v pf , v cc > v backup no v cc v cc > v pf , v cc < v backup yes v cc v cc > v pf , v cc > v backup yes v cc parameter symbol min typ max units nominal frequency f o 32.768 khz series resistance esr 50 k ? load capacitance c l 6pf * the crystal, traces, and crystal input pins should be isolated from rf generating signals. refer to application note 58: crystal considerations for dallas real-time clocks for addi- tional specifications. table 1. power control table 2. crystal specifications*
ds1388 clock accuracy the accuracy of the clock is dependent upon the accu- racy of the crystal and the accuracy of the match between the capacitive load of the oscillator circuit and the capacitive load for which the crystal was trimmed. additional error is added by crystal frequency drift caused by temperature shifts. external circuit noise coupled into the oscillator circuit can result in the clock running fast. figure 4 shows a typical pc board layout for isolation of the crystal and oscillator from noise. refer to application note 58: crystal considerations with dallas real-time clock s for detailed information. address map figure 5 shows the address map for the ds1388. the memory map is divided into three blocks. the memory block accessed is determined by the value of the block address bits in the slave address byte. the timekeep- ing registers reside in block 0h. during a multibyte access of the timekeeping registers, when the internal address pointer reaches 0ch, it wraps around to loca- tion 00h. on an i 2 c start or address pointer incre- menting to location 00h, the current time is transferred to a second set of registers. the time information is read from these secondary registers, while the clock may continue to run. this eliminates the need to reread the registers in case the main registers update during a read. the eeprom is divided into two 256-byte blocks located in blocks 1h and 2h. during a multibyte read of the eeprom registers, when the internal address point- er reaches ffh, it wraps around to location 00h of the block of eeprom specified in the block address. during a multibyte write of the eeprom registers, when the internal address pointer reaches the end of the cur- rent 8-byte eeprom page, it wraps around to the beginning of the eeprom page. see the write operation section for details. to avoid rollover issues when writing to the time and date registers, all registers should be written before the hundredths-of-seconds register reaches 99 (bcd). hundredths-of-seconds generator the hundredths-of-seconds generator circuit shown in the block diagram is a state machine that divides the incoming frequency (4096hz) by 41 for 24 cycles and 40 for 1 cycle. this produces a 100hz output that is slightly off during the short term, and is exactly correct every 250ms. the divide ratio is given by: ratio = [41 x 24 + 40 x 1] / 25 = 40.96 thus, the long-term average frequency output is exactly 100hz. i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom 10 ____________________________________________________________________ countdown chain x1 x2 crystal c l 1c l 2 r tc registers ds1388 figure 3. oscillator circuit showing internal bias network local ground plane (layer 2) crystal gnd x2 x1 note: avoid routing signal lines in the crosshatched area (upper left quadrant) of the package unless there is a ground plane between the signal line and the device package. figure 4. layout example
ds1388 i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom ____________________________________________________________________ 11 address blk word bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 function range 0h 00h tenth seconds hundredths of seconds hundredths of seconds 00?9 0h 01h 0 10 seconds seconds seconds 00?9 0h 02h 0 10 minutes minutes minutes 00?9 am / pm 10 hour 0h 03h 0 12/ 24 10 hour hours hours 1?2+ am /pm 00?3 0h 04h 0 0 0 0 x day day 01?7 0h 05h 0 0 10 date date date 00?1 0h 06h 0 0 x 10 month month month 01?2 0h 07h 10 year year year 00?9 0h 08h watchdog tenths of seconds watchdog hundredths of seconds watchdog hundredth seconds 00?9 0h 09h watchdog tenths of seconds watchdog seconds watchdog seconds 00?9 0h 0ah tcs3 tcs2 tcs1 tcs0 ds1 ds0 rout1 rout0 trickle charger 0h 0bh osf wf 0 0 0 0 0 0 flag 0h 0ch eosc 00 0 0 0 wde wd/ rst control 1h 00?fh 256 x 8 eeprom eeprom 00?fh 2h 00?fh 256 x 8 eeprom eeprom 00?fh figure 5. address map note: unless otherwise specified, the state of the registers is not defined when power (v cc and v backup ) is first applied. x = general-purpose read/write bit. 0 = always reads as a zero. clock and calendar the time and calendar information is obtained by read- ing the appropriate register bytes. figure 5 illustrates the rtc registers. the time and calendar are set or ini- tialized by writing the appropriate register bytes. the contents of the time and calendar registers are in the binary-coded decimal (bcd) format. the end of the month date is automatically adjusted for months with fewer than 31 days, including corrections for leap years through 2099. the day-of-week register increments at midnight. values that correspond to the day-of-week are user-defined but must be sequential (i.e., if 1 equals sunday, then 2 equals monday, and so on). illogical time and date entries result in undefined oper- ation. the ds1388 can be run in either 12-hour or 24- hour mode. bit 6 of the hours register is defined as the 12- or 24-hour mode-select bit. when high, the 12-hour mode is selected. in the 12-hour mode, bit 5 is the am /pm bit with logic-high being pm. in the 24-hour mode, bit 5 is the second 10-hour bit (20?3 hours). changing the 12/ 24 bit requires that the hours data be re-entered in the proper format.
ds1388 w atchdog alarm counter the contents of the watchdog alarm counter, which is a separate two-byte bcd down counter, are accessed in the address range 08h?9h in block 0h. it is programma- ble in 10ms intervals from 0.01 to 99.99 seconds. when this counter is written, both the counter and a seed regis- ter are loaded with the desired value. when the counter is to be reloaded, it uses the value in the seed register. when the counter is read, the current counter value is latched into a register, which is output on the serial data line while the counter continues to decrement. if the counter is not needed, it can be disabled and used as a 16-bit cache of battery-backed ram by set- ting the wde bit in the control register to logic 0. if all 16 bits of the watchdog alarm counter are written to a zero when wde = 1, the counter is disabled and the wf bit is not set. when the wde bit in the control register is set to a logic 1 and a non-zero value is written into the watchdog reg- isters, the watchdog alarm counter decrements every 1/100 second, until it reaches zero. at this point, the wf bit in the flag register is set. if wd/ rst = 1, the rst pin is pulsed low for t rst and access to the ds1388 is inhibited. at the end of t rst , the rst pin becomes high impedance, and read/write access to the ds1388 is enabled. the wf flag remains set until cleared by writ- ing wf to logic 0. the watchdog alarm counter can be reloaded and restarted before the counter reaches zero by reading or writing any of the watchdog alarm counter registers. the wde bit must be set to zero before writing the watchdog registers. after writing the watchdog regis- ters, wde must be set to one to enable the watchdog. power-up/down, reset, and pushbutton reset functions a precision temperature-compensated reference and comparator circuit monitors the status of v cc . when an out-of-tolerance condition occurs, an internal power-fail signal is generated that blocks read/write access to the device and forces the rst pin low. when v cc returns to an in-tolerance condition, the internal power-fail sig- nal is held active for t rst to allow the power supply to stabilize, and the rst pin is held low. if the eosc bit is set to a logic 1 (to disable the oscillator in battery-back- up mode), the internal power-fail signal and the rst pin are kept active for t rst plus the oscillator startup time. the ds1388 provides for a pushbutton switch to be connected to the rst output pin. when the ds1388 is not in a reset cycle, it continuously monitors the rst signal for a low-going edge. if an edge is detected, the part debounces the switch by pulling the rst pin low and inhibits read/write access. after the internal timer has expired, the part continues to monitor the rst line. if the line is still low, it continues to monitor the line look- ing for a rising edge. upon detecting release, the part forces the rst pin low and holds it low for t rst . special-purpose registers the ds1388 has three additional registers (control, flag, and trickle charger) that control the real-time clock, watchdog, and trickle charger. flag register (00bh) bit 7: oscillator stop flag (osf). a logic 1 in this bit indicates that the oscillator has stopped or was stopped for some period of time and may be used to judge the validity of the clock and calendar data. this bit is edge triggered and is set to logic 1 when the internal circuitry senses the oscillator has transitioned from a normal run state to a stop condition. the follow- ing are examples of conditions that can cause the osf bit to be set: 1) the first time power is applied. 2) the voltage present on both v cc and v backup are insufficient to support oscillation. 3) the eosc bit is turned off. 4) external influences on the crystal (i.e., noise, leak- age, etc.). this bit remains at logic 1 until written to logic 0. this bit can only be written to logic 0. attempting to write osf to logic 1 leaves the value unchanged. bit 6: watchdog alarm flag (wf). a logic 1 in this bit indicates that the watchdog counter reached zero. if wde and wd/ rst are set to 1, the rst pin pulses low for t rst when the watchdog counter reaches zero and sets wf = 1. at the completion of the pulse, the wf bit remains set to logic 1. writing this bit to logic 0 clears the wf flag. this bit can only be written to logic 0. attempting to write logic 1 leaves the value unchanged. bits 5 to 0: these bits read as zero and cannot be modified. i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom 12 ____________________________________________________________________ flag register (00bh) bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 osf wf 0 00000
ds1388 i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom ____________________________________________________________________ 13 control register (00ch) bit 7: enable oscillator ( eosc ). when set to logic 0, the oscillator is started. when set to logic 1, the oscilla- tor is stopped when the ds1388 switches to battery power. this setting can be used to conserve battery power when timekeeping operation is not required. this bit is cleared (logic 0) when power is first applied. when the ds1388 is powered by v cc , the oscillator is always on regardless of the status of the eosc bit. bits 6 to 2: these bits read as zero and cannot be modified. bit 1: watchdog enable (wde). when set to logic one, the watchdog counter is enabled. when set to logic 0, the watchdog counter is disabled, and the two registers can be used as nv ram. this bit is cleared (logic 0) when power is first applied. bit 0: watchdog reset (wd/ rst ). this bit enables the watchdog alarm output to drive the rst pin. when the wd/ rst bit is set to logic 1, rst pulses low for t rst if wde = 1 and the watchdog counter reaches zero. when the wd/ rst bit is set to logic 0, the rst pin is not driven by the watchdog alarm; only the watchdog flag bit (wf) in the flag register is set to logic 1. this bit is logic 0 when power is first applied. trickle-charge register (00ah) the simplified schematic of figure 6 shows the basic components of the trickle charger. the trickle-charge select (tcs) bits (bits 4?) control the selection of the trickle charger. to prevent accidental enabling, only a pattern on 1010 enables the trickle charger. all other patterns disable it. the trickle charger is disabled when power is first applied. the diode-select (ds) bits (bits 2 and 3) select whether or not a diode is connected between v cc and v backup . if ds is 01, no diode is selected, yet if ds is 10, a diode is selected. the rout bits (bits 0 and 1) select the value of the resistor con- nected between v cc and v backup . table 3 shows the resistor selected by the resistor select (rout) bits and the diode selected by the diode-select (ds) bits. warning: the rout value of 250 ? must not be select- ed whenever v cc is greater than 3.63v. the user determines the diode and resistor selection according to the maximum current desired for battery or super cap charging. the maximum charging current can be calculated as illustrated in the following exam- ple. assume that a system power supply of 3.3v is applied to v cc and a super cap is connected to v backup . also, assume that the trickle charger has been enabled with a diode and resistor r2 between v cc and v backup . the maximum current i max would be calculated as follows: i max = (3.3v - diode drop) / r2 (3.3v - 0.7v) / 2k ? 1.3ma as the super cap charges, the voltage drop between v cc and v backup decreases and therefore the charge current decreases. control register (00ch) bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 eosc 00000wdewd/ rst table 3. trickle-charge register tcs3 tcs2 tcs1 tcs0 ds1 ds0 rout1 rout0 function xxx x0 0x x disabled xxx x1 1x x disabled xxx xxx 00 disabled 10100101no diode, 250 ? resistor 10101001 one diode, 250 ? resistor 10100110no diode, 2k ? resistor 10101010 one diode, 2k ? resistor 10100111no diode, 4k ? resistor 10101011 one diode, 4k ? resistor 00000000 initial default value?isabled
ds1388 eeprom the ds1388 provides 512 bytes of eeprom organized into two blocks of 256 bytes. each 256-byte block is divided into 32 pages consisting of 8 bytes per page. the eeprom can be written one page at a time. page write operations are limited to writing bytes within a sin- gle physical page, regardless of the number of bytes actually being written. physical page boundaries start at addresses that are integer multiples of the page size (8 bytes) and end at addresses that are integer multiples of [page size -1]. for example, page 0 contains word addresses 00h to 07h. similarly, page 1 contains word addresses 08h to 0fh. if a page write command attempts to write across a physical page boundary, the result is that the data wraps around to the beginning of the current page (overwriting data previously stored there), instead of being written to the next page as might be expected. therefore, it is necessary for the application software to prevent page write operations that would attempt to cross a page boundary. i 2 c serial data bus the ds1388 supports a bidirectional i 2 c bus and data transmission protocol. a device that sends data onto the bus is defined as a transmitter and a device receiv- ing data is defined as a receiver. the device that con- trols the message is called a master. the devices that are controlled by the master are slaves. the bus must be controlled by a master device that generates the serial clock (scl), controls the bus access, and gener- ates the start and stop conditions. the ds1388 operates as a slave on the i 2 c bus. connections to the bus are made through the open-drain i/o lines sda and scl. within the bus specifications, a standard mode (100khz maximum clock rate) and a fast mode (400khz maximum clock rate) are defined. the ds1388 works in both modes. the following bus protocol has been defined (figure 7): data transfer may be initiated only when the bus is not busy. during data transfer, the data line must remain stable whenever the clock line is high. changes in the data line while the clock line is high will be interpreted as control signals. accordingly, the following bus conditions have been defined: bus not busy: both data and clock lines remain high. start data transfer: a change in the state of the data line from high to low, while the clock line is high, defines a start condition. stop data transfer: a change in the state of the data line from low to high, while the clock line is high, defines a stop condition. data valid: the state of the data line represents valid data when, after a start condition, the data line is stable for the duration of the high period of the clock signal. the data on the line must be changed during the low period of the clock signal. there is one clock pulse per bit of data. i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom 14 ____________________________________________________________________ r1 250 ? r2 2k ? r3 4k ? v cc v backup bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 tcs3 tcs2 tcs1 tcs0 ds1 ds0 rout1 rout0 trickle-charge register (00ah) 1 0f 16 select note: only 1010b enables charger 1 of 2 select 1 of 3 select tcs 0-3 = trickle-charge select ds 0-1 = diode select rout 0-1 = resistor select figure 6. programmable trickle charger
each data transfer is initiated with a start condition and terminated with a stop condition. the number of data bytes transferred between the start and the stop conditions is not limited, and is determined by the master device. the information is transferred byte-wise and each receiver acknowledges with a ninth bit. acknowledge: each receiving device, when addressed, is obliged to generate an acknowledge (ack) after the reception of each byte. the master device must generate an extra clock pulse, which is associated with this acknowledge bit. the ds1388 does not generate any acknowledge bits if access to the eeprom is attempted during an internal pro- gramming cycle. a device that acknowledges must pull down the sda line during the acknowledge clock pulse in such a way that the sda line is stable low during the high period of the acknowledge-related clock pulse. of course, setup and hold times must be taken into account. a master must signal an end of data to the slave by generating a not-acknowledge (nack) bit on the last byte that has been clocked out of the slave. in this case, the slave must leave the data line high to enable the master to generate the stop condition. figures 8 and 9 detail how data transfer is accom- plished on the i 2 c bus. depending upon the state of the r/ w bit, two types of data transfer are possible: data transfer from a master transmitter to a slave receiver. the first byte transmitted by the master is the slave address. next follows a number of data bytes. the slave returns an acknowledge bit after each received byte. data are transferred with the most significant bit (msb) first. data transfer from a slave transmitter to a master receiver. the first byte (the slave address) is trans- mitted by the master. the slave then returns an acknowledge bit. next follows a number of data bytes transmitted by the slave to the master. the master returns an acknowledge bit after all received bytes other than the last byte. at the end of the last received byte, a nack is returned. the master device generates all the serial clock pulses and the start and stop conditions. a trans- fer is ended with a stop condition or with a repeat- ed start condition. since a repeated start condition is also the beginning of the next serial transfer, the bus is not released. data are transferred with the most significant bit (msb) first. ds1388 i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom ____________________________________________________________________ 15 stop condition or repeated start condition repeated if more bytes are transfered ack start condition ack acknowledgement signal from receiver acknowledgement signal from receiver slave address msb scl sda r/w direction bit 12 678 9 12 89 3? figure 7. i 2 c data transfer overview
ds1388 device addressing the slave address byte is the first byte received follow- ing the start condition from the master device. the slave address byte consists of a 4-bit control code. for the ds1388, this is set as 1101 binary for read and write operations. the next three bits of the slave address byte are the block select bits (b2, b1, b0). b2 is always logic 0 for the ds1388. these bits are used by the master device to select which of the three blocks in the memory map are to be accessed. these bits are the three most significant bits of the word address. the last bit of the slave address byte defines the operation to be performed. when set to 1, a read operation is selected; when set to 0, a write operation is selected. w rite operation slave receiver mode (write mode) following the start condition from the master, the device code (4 bits); the block address (3 bits); and the r/ w bit, which is logic-low, is placed onto the bus by the master transmitter. this indicates to the ds1388 that a byte with a word address follows after the ds1388 has generated an acknowledge bit during the ninth clock cycle. the next byte transmitted by the master is the word address and will set the internal address pointer of the ds1388, with the ds1388 acknowledging the transfer on the ninth clock cycle. the master device can then transmit zero or more bytes of data, with the ds1388 acknowledging the transfer on the ninth clock cycle. the master generates a stop condition to terminate the data write. byte write the write-slave address byte and word address are transmitted to the ds1388 as described in the slave receiver mode section. the master transmits one data byte, with the ds1388 acknowledging the transfer on the ninth clock cycle. the master then generates a stop condition to terminate the data write. this initiates the internal write cycle, and, if the write was to the eeprom, the ds1388 does not generate acknowledge signals during the internal eeprom write cycle. eeprom page write the write-slave address byte, word address, and the first data byte are transmitted to the ds1388 in the same way as in a byte write. but instead of generating a stop condition, the master transmits up to 8 data bytes to the ds1388, which are temporarily stored in the on-chip page buffer and are written into the memo- ry after the master has transmitted a stop condition. data bytes within the page that are not written remain unchanged. the internal address pointer automatically increments after each byte is written. if the master should transmit more than 8 data bytes prior to generating the stop condition, the address pointer rolls over and the previously received data is overwritten. as with the byte write operation, once the stop condi- tion is received an internal write cycle begins. rtc multibyte write writing multiple bytes to the rtc works much the same way as the eeprom page write, except that the entire contents of block 0h can be written at once. the 8-byte page size limitation does not apply to the block 0. if the master should transmit more bytes than exists in block 0 prior to generating the stop condition, the internal address pointer rolls over and the previously received data is overwritten. as with the byte write operation, once the stop condition is received an internal write cycle begins. i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom 16 ____________________________________________________________________ slave address byte bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 1101b2b 1b0r/ w operation control code block select r/ w read clock 1101 000 1 write clock 1101 000 0 read lower block of eeprom 1101 001 1 write lower block of eeprom 1101 001 0 read upper block of eeprom 1101 010 1 write upper block of eeprom 1101 010 0
acknowledge polling since the ds1388 does not acknowledge during an eeprom write cycle, acknowledge polling can be used to determine when the cycle is complete (this feature can be used to maximize bus throughput). once the master issues the stop condition for a write command, the ds1388 initiates the internally timed write cycle. ack polling can be initiated immediately. this involves the master sending a start condition, followed by the slave address byte for a write command (r/ w = 0) to the eeprom. if the device is still busy with the write cycle, then a nack is returned. if the cycle is com- plete, then the device returns the ack and the master can then proceed with the next read or write command. the rtc registers in block 0 are accessible during an eeprom write cycle. read operation read operations are initiated in the same way as write operations with the exception that the r/ w bit of the slave address is set to 1. there are three basic types of read operations: current address read, random read, and sequential read. current address read the ds1388 contains an address pointer that main- tains the last address accessed, internally increment- ed by 1. therefore, if the previous access (either a read or write operation) was to address n, the next cur- rent address read operation would access data from address n + 1. upon receipt of the slave address with the r/ w bit set to 1, the ds1388 issues an acknowl- edge and transmits the 8-bit data byte. the master issues a nack followed by a stop condition, and the ds1388 discontinues transmission. random read random read operations allow the master to access any memory location in a random manner. to perform this type of read operation, first the word address must be set. this is done by sending the word address to the ds1388 as part of a write operation. after the word address is sent, the master generates a start condi- tion following the acknowledge. this terminates the write operation, but not before the internal address pointer is set. then the master issues the slave address byte again but with the r/ w bit set to 1. the ds1388 then issues an acknowledge and transmits the 8-bit data byte. the master issues a nack followed by a stop condition, and the ds1388 discontinues transmission. sequential read sequential reads are initiated in the same way as a ran- dom read except that after the ds1388 transmits the first data byte, the master issues an acknowledge as opposed to a stop condition in a random read. this directs the ds1388 to transmit the next sequentially addressed 8-bit byte. to provide sequential reads, the ds1388 contains an internal address pointer, which is incremented by one at the completion of each opera- tion. this allows the entire memory contents of the block specified in the slave address to be serially read during one operation. the master terminates the read by generating a nack followed by a stop condition. no page boundaries exist for read operations. when the address pointer reaches the end of an eeprom block (ffh), the address pointer wraps to the beginning (00h) of the same block. the ds1388 can operate in the two modes illustrated in figure 8 and 9. ds1388 i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom ____________________________________________________________________ 17 a xxxxxxxx a 1101bbb s 0 xxxxxxxx a xxxxxxxx a xxxxxxxx a p b = block select s = start a = acknowledge p = stop r/w = read/write or direction bit address data transferred (x + 1 bytes + acknowledge) figure 8. slave receiver mode (write mode) a xxxxxxxx a 1101bbb s 1 xxxxxxxx a xxxxxxxx a xxxxxxxx a p b = block select s = start a = acknowledge p = stop a = not acknowledge r/w = read/write or direction bit address data transferred (x + 1 bytes + acknowledge) note: last data byte is followed by a not acknowledge (a) signal figure 9. slave transmitter mode (read mode)
ds1388 i 2 c rtc/supervisor with trickle charger and 512 bytes eeprom maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 18 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2005 maxim integrated products printed usa is a registered trademark of maxim integrated products, inc. is a registered trademark of dallas semiconductor corporation. package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation, go to www.maxim-ic.com/dallaspackinfo ) . chip information transistor count: 25,527 substrate connected to ground process: cmos thermal information theta-ja: +170?/w theta-jc: +40?/w
e nglish ? ???? ? ??? ? ??? what's ne w p roducts solutions de sign ap p note s sup p ort buy comp any me mbe rs ds1388 part number table notes: see the ds1388 quickview data sheet for further information on this product family or download the ds1388 full data sheet (pdf, 392kb). 1. other options and links for purchasing parts are listed at: http://www.maxim-ic.com/sales . 2. didn't find what you need? ask our applications engineers. expert assistance in finding parts, usually within one business day. 3. part number suffixes: t or t&r = tape and reel; + = rohs/lead-free; # = rohs/lead-exempt. more: see full data sheet or part naming c onventions . 4. * some packages have variations, listed on the drawing. "pkgc ode/variation" tells which variation the product uses. 5. part number free sample buy direct package: type pins size drawing code/var * temp rohs/lead-free? materials analysis ds1388z-3 soic ;8 pin;150 dwg: 56-g2008-001c (pdf) use pkgcode/variation: s8-4 * -40c to +85c rohs/lead-free: no materials analysis ds1388z-33 soic ;8 pin;150 dwg: 56-g2008-001c (pdf) use pkgcode/variation: s8-4 * -40c to +85c rohs/lead-free: no materials analysis ds1388z-5 soic ;8 pin;150 dwg: 56-g2008-001c (pdf) use pkgcode/variation: s8-4 * -40c to +85c rohs/lead-free: no materials analysis ds1388z-3+ soic ;8 pin;150 dwg: 56-g2008-001c (pdf) use pkgcode/variation: s8+4 * -40c to +85c rohs/lead-free: yes materials analysis ds1388z-33+ soic ;8 pin;150 dwg: 56-g2008-001c (pdf) use pkgcode/variation: s8+4 * -40c to +85c rohs/lead-free: yes materials analysis ds1388z-5+ soic ;8 pin;150 dwg: 56-g2008-001c (pdf) use pkgcode/variation: s8+4 * -40c to +85c rohs/lead-free: yes materials analysis ds1388z-33+t&r soic ;8 pin;150 dwg: 56-g2008-001c (pdf) use pkgcode/variation: s8+4 * -40c to +85c rohs/lead-free: yes materials analysis didn't find what you need?
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