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1 of 19 073102 note: some revisions of this device may incorporate deviations from published specifications known as errata. multiple revisions of a ny device may be simultaneously available through various sales channels. for information about device errata, click here: http://www.maxim-ic.com/errata . features drop-in replacement for ibm at computer clock/calendar pin-compatible with the mc146818b and ds1287 totally nonvolatile with over 10 years of operation in the absence of power self-contained subsystem includes lithium, quartz, and support circuitry counts seconds, minutes, hours, days, day of the week, date, month, and year with leap- year compensation valid up to 2100 binary or bcd representation of time, calendar, and alarm 12-hour or 24-hour clock with am and pm in 12-hour mode daylight savings time option selectable between motorola and intel bus timing multiplex bus for pin efficiency interfaced with software as 128 ram locations ? 14 bytes of clock and control registers ? 114 bytes of general-purpose ram programmable square-wave output signal bus-compatible interrupt signals ( irq ) three interrupts are separately software- maskable and testable ? time-of-day alarm once/second to once/day ? periodic rates from 122ms to 500ms ? end-of-clock update cycle underwriters laboratory (ul) recognized pin assignment (top view) package dimension information http://www.maxim-ic.com/techsupport/dallaspackinfo.htm pin description ad0?ad7 ? multiplexed address/data bus n.c. ? no connection mot ? bus type selection cs ? chip select as ? address strobe r/ w ? read/write input ds ? data strobe reset ? reset input irq ? interrupt request output sqw ? square-wave output v cc ? +5v supply gnd ? ground ordering information part pin-package top mark temp range DS12887 24 pdip module DS12887 0c to +70c nc DS12887 real-time clock www.maxim-ic.com www.maxim-ic.com DS12887 24 pdip module (700mil)
DS12887 2 of 19 typical operating circuit description the DS12887 real-time clock (rtc) plus ram is desi gned to be a direct replacement for the ds1287. the DS12887 is identical in form, fit, and functi on to the ds1287, and has an additional 64 bytes of general-purpose ram. access to this additional ram space is determined by the logic level presented on ad6 during the address portion of an access cycle. a lithium energy source, quartz crystal, and write- protection circuitry are contained within a 24-pin dual in-line package. as such, the DS12887 is a complete subsystem replacing 16 components in a ty pical application. the f unctions include a nonvolatile time-of-day clock, an alarm, a 100-year calendar, pr ogrammable interrupt, square-wave generator, and 114 bytes of nv sram. the rtc is unique in that time -of-day and memory are maintained even in the absence of power. operation the block diagram in figure 1 shows the pin connec tions with the major internal functions of the DS12887. the following paragraphs desc ribe the function of each pin.
DS12887 3 of 19 figure 1 . block diagram power-up/down considerations the rtc function continues to operate, and all of the ram, time, calendar, and alarm memory locations remain nonvolatile regardless of the level of the v cc input. when v cc is applied to the DS12887 and reaches a level of greater than 4.25v, the device becomes accessible after 200ms, provided that the oscillator is running and the osc illator countdown chain is not in re set (register a). this time period allows the system to stabilize after power is applied. when v cc falls below 4.25v, the chip-select input is internally forced to an inactive level regardless of the value of cs at the input pin. the DS12887 is, therefore, write-protected. when the DS12887 is in a wr ite-protected state, all inputs are ignored and all outputs are in a high-impedance state. when v cc falls below a level of approximately 3v, the external v cc supply is switched off, and an internal lithium energy source supplies power to the rtc and the ram memory.
DS12887 4 of 19 signal descriptions gnd, v cc ? dc power is provided to the device on these pins. v cc is the +5v input. when 5v are applied within normal limits, the device is fully acce ssible and data can be written and read. when v cc is below 4.25v typical, reads and writes are inhibite d. however, the timekeeping function continues unaffected by the lower input voltage. as v cc falls below 3v typical, the ram and timekeeper are switched over to an internal lithium energy source. the timekeeping function maintains an accuracy of 1 minute per month at +25 c, regardless of the voltage input on the v cc pin. mot (mode select) ? the mot pin offers the flexibility to choose between two bus types. when connected to v cc , motorola bus timing is selected. when c onnected to gnd or left disconnected, intel bus timing is selected. the pin has an internal pulldown resistance of approximately 20k . sqw (square-wave output) ? the sqw pin can output a signal from one of 13 taps provided by the 15 internal divider stages of the rtc. the frequency of the sqw pin can be changed by programming register a, as shown in table 1. the sqw signal can be turned on and off using the sqwe bit in register b. the sqw signal is not available when v cc is less than 4.25v, typically. table 1 . periodic interrupt rate and square-wave output frequency select bits register a rs3 rs2 rs1 rs0 t pi periodic interrupt rate sqw output frequency 0 0 0 0 none none 0 0 0 1 3.90625ms 256hz 0 0 1 0 7.8125ms 128hz 0011 122.070 s 8.192khz 0100 244.141 s 4.096khz 0101 488.281 s 2.048khz 0110 976.5625 s 1.024khz 0 1 1 1 1.953125ms 512hz 1 0 0 0 3.90625ms 256hz 1 0 0 1 7.8125ms 128hz 1 0 1 0 15.625ms 64hz 1 0 1 1 31.25ms 32hz 1 1 0 0 62.5ms 16hz 1 1 0 1 125ms 8hz 1 1 1 0 250ms 4hz 1 1 1 1 500ms 2hz ad0?ad7 (multiplexed bidirectional address/data bus) ? multiplexed buses save pins because address information and data information time-share the same signal paths. the addresses are present during the first portion of the bus cycle and the same pi ns and signal paths are used for data in the second portion of the cycle. address/data multiplexing does not slow the access time of the DS12887 since the bus change from address to data occurs during the internal ram access time. addresses must be valid prior to the falling edge of as/ ale, at which time the DS12887 latches the address from ad0 to ad6. valid write data must be present and held stable during the latter portion of the ds or wr pulses. in a read cycle the DS12887 outputs 8 bits of data during the latter portion of the ds or rd pulses. the read
DS12887 5 of 19 cycle is terminated and the bus returns to a high-impedance state as ds transitions low in the case of motorola timing or as rd transitions high in the case of intel timing. as (address strobe input) ? a positive-going address-strobe pulse serves to demultiplex the bus. the falling edge of as/ale causes the address to be latched within the DS12887. the next rising edge that occurs on the as bus clears the address regardless of whether cs is asserted. access commands should be sent in pairs. ds (data strobe or read input) ? the ds/ rd pin has two modes of opera tion depending on the level of the mot pin. when the mot pin is connected to v cc , motorola bus timing is selected. in this mode, ds is a positive pulse during the latter portion of the bus cycle and is called data strobe. during read cycles, ds signifies the time that the DS12887 is to driv e the bidirectional bus. in write cycles the trailing edge of ds causes the DS12887 to la tch the written data. when the mot pin is connected to gnd, intel bus timing is selected. in this mode the ds pin is called read ( rd ). rd identifies the time period when the DS12887 drives the bus with read data. the rd signal is the same defi nition as the output-enable ( oe ) signal on a typical memory. r/ w (read/write input) ? the r/ w pin also has two modes of operation. when the mot pin is connected to v cc for motorola timing, r/ w is at a level that indicates whether the current cycle is a read or write. a read cycle is indicated with a high level on r/ w while ds is high. a write cycle is indicated when r/ w is low during ds. when the mot pin is connected to gnd for intel timing, the r/ w signal is an active-low signal called wr. in this mode, the r/ w pin has the same meaning as the write-enable signal ( we ) on generic rams. cs (chip-select input) ? the chip select signal must be a sserted low for a bus cycle in the DS12887 to be accessed. cs must be kept in the active state during ds and as for motorola timing and during rd and wr for intel timing. bus cycles th at take place without asserting cs latch addresses but no access occur. when v cc is below 4.25v, the DS12887 internally inhib its access cycles by internally disabling the cs input. this action protects both the rtc da ta and ram data during power outages. irq (interrupt request output) ? the irq pin is an active-low output of the DS12887 that can be used as an interrupt input to a processor. the irq output remains low as long as the status bit causing the interrupt is present and the corresponding in terrupt-enable bit is set. to clear the irq pin, the processor program normally reads the c register. the reset pin also clears pending interrupts. when no interrupt conditions are present, the irq level is in the high-impedance state. multiple interrupting devices can be connected to an irq bus. the irq bus is an open drain output and requires an external pullup resistor. reset (reset input) ? the reset pin has no affect on the clock, ca lendar, or ram. on power-up, the reset pin can be held low for a time to allow the power supply to stabilize. the amount of time that reset is held low is dependent on the application. however, if reset is used on power-up, the time
DS12887 6 of 19 reset is low should exceed 200ms to ensure that the internal timer that controls the DS12887 on power- up has timed out. when reset is low and v cc is above 4.25v, the following occurs: a) periodic interrupt enable (pei) bit is cleared to 0. b) alarm interrupt enable (aie) bit is cleared to 0. c) update ended interrupt flag (uf) bit is cleared to 0. d) interrupt request status flag (irqf) bit is cleared to 0. e) periodic interrupt flag (pf) bit is cleared to 0. f) the device is not accessible until reset is returned high. g) alarm interrupt flag (af) bit is cleared to 0. h) h. irq pin is in the high impedance state. i) square-wave output enable ( sqwe ) bit is cleared to 0. j) update ended interrupt enab le (uie) is cleared to 0. in a typical application reset can be connected to v cc . this connection allows the DS12887 to go in and out of power fail without affec ting any of the control registers. address map the address map of the DS12887 is shown in figure 2. the address map consists of 114 bytes of user ram; 10 bytes of ram that contain the rtc time, calendar, and alarm data; and 4 bytes that are used for control and status. all 128 bytes can be direct ly written or read except for the following: 1) registers c and d are read-only. 2) bit 7 of register a is read-only. 3) the high-order bit of the seconds byte is read-only. the contents of four registers (a, b, c, and d) are described in the registers section. figure 2. address map
DS12887 7 of 19 time, calendar, and alarm locations the time and calendar information is obtained by reading the appropriate memory bytes. the time, calendar, and alarm are set or initialized by writing the appropriate ram bytes. the contents of the 10 time, calendar, and alarm bytes can be either binary or binary coded decimal (bcd) format. before writing the internal time, calendar, and alarm registers, the set bit in register b should be written to a logic 1 to prevent updates from occurring while acce ss is being attempted. in addition to writing the 10 time, calendar, and alarm registers in a selected format (binary or bcd), the data mode bit (dm) of register b must be set to the appropriate logic level. all 10 time, calendar, and alarm bytes must use the same data mode. the set b it in register b should be cleared afte r the data mode bit has been written to allow the rtc to update the time a nd calendar bytes. once initialized, the rtc makes a ll updates in the selected mode. the data mode cannot be changed without reinitializing the 10 data bytes. table 2 shows the binary and bcd formats of the 10 time, cale ndar, and alarm locations. the 24?12 bit cannot be changed without reinitializing the hour locations. when the 12-hour format is selected, the high-order bit of the hours byte represents pm when it is a lo gic 1. the time, calendar, and alarm bytes are always accessible because they are double buffered. the 10 by tes are advanced once per second by 1 second and checked for an alarm condition. if a read of the time and calendar data occurs during an update, a problem exists where seconds, minutes, hours, etc., might not correlate. the probability of reading incorrect time and calendar data is low. several methods of avoiding any possible in correct time and calendar reads are covered later in this text. the three alarm bytes can be used in two ways. first, when the alarm time is written in the appropriate hours, minutes, and seconds alarm locations, the alarm in terrupt is initiated at the specified time each day if the alarm enable bit is high. the second use condition is to insert a ?don?t care ? state in one or more of the three alarm bytes. the ?don?t care? code is any hexadecimal value from c0 to ff. the two most significant bits of each byte set the ?don?t care? condition when at logic 1. an alarm is generated each hour when the ?don?t care? bits are set in the hours byte. similarly, an alarm is generated every minute with ?don?t care? codes in the hours and minute alarm bytes. the ?don?t care? codes in all three alarm bytes create an interrupt every second. table 2. time, calendar, and alarm data modes data mode range address location function decimal range binary bcd 0 seconds 0?59 00?3b 00?59 1 seconds alarm 0?59 00?3b 00?59 2 minutes 0?59 00?3b 00?59 3 minutes alarm 0?59 00?3b 00?59 hours, 12-hour mode 1?12 01?0c am, 81?8c pm 01?12am, 81?92pm 4 hours, 24-hour mode 0?23 00?17 00?23 hours alarm, 12-hour 1?12 01?0c am, 81?8c pm 01?12am, 81?92pm 5 hours alarm, 24-hourr 0?23 00?17 00?23 6 day of the week sunday = 1 1?7 01?07 01?07 7 date of the month 1?31 01?1f 01?31 8 month 1?12 01?0c 01?12 9 year 0?99 00?63 00?99
DS12887 8 of 19 nv ram the 114 general-purpose nv ram bytes are not dedicat ed to any special function within the DS12887. they can be used by the processor program as nonvolatile memory and are fu lly available during the update cycle. interrupts the rtc plus ram includes three separate, fully auto matic sources of interrupt for a processor. the alarm interrupt can be programmed to occur at rates from once per second to once per day. the periodic interrupt can be selected for rates from 500ms to 122 s. the update-ended interrupt can be used to indicate to the program that an update cycle is comple te. each of these independe nt interrupt conditions is described in greater detail in other sections of this text. the processor program can select which interrupts, if any, are going to be used. three bits in register b enable the interrupts. writing a logic 1 to an interrupt-enable bit permits that interrupt to be initiated when the event occurs. a 0 in an interrupt-enable bit prohibits the irq pin from being asserted from that interrupt condition. if an interrupt flag is already set when an interrupt is enabled, irq is immediately set at an active level, although the interrupt initiating the event may have occurred much earlier. as a result, there are cases where the program should clear such earlier initiated interrupts before first enabling new interrupts. when an interrupt event occurs, the relating flag bit is set to logic 1 in register c. these flag bits are set independently of the state of the co rresponding enable bit in register b. the flag bit can be used in a polling mode without enabling the corresponding enable bits. the interrupt flag bit is a status bit that software can interrogate as necessary. when a flag is set, an indication is given to software that an interrupt event has occurred since the flag bit was la st read; however, care should be taken when using the flag bits as they are cleared each time register c is read. double latching is included with register c so that set bits remain stable throughout the read cycle. all bits that are set (high) are cleared when read and new interrupts that are pending during the read cycle are held until after the cycle is completed. one, two, or three bits can be set when reading register c. each used flag bit should be examined when read to ensure that no interrupts are lost. the second flag bit usage method is with fully enabled in terrupts. when an interrupt flag bit is set and the corresponding interrupt-enable bit is also set, the irq pin is asserted low. irq is asserted as long as at least one of the three interrupt sources has its flag and enable bits both set. the irqf bit in register c is a 1 whenever the irq pin is being driven low. determination that the rtc initiated an interrupt is accomplished by reading register c. a logic 1 in bit 7 (irqf bit) indicates that one or more interrupts have been initiated by the DS12887. the act of reading re gister c clears all active flag bits and the irqf bit.
DS12887 9 of 19 oscillator control bits when the DS12887 is shipped from the factory, the intern al oscillator is turned off. this feature prevents the lithium energy cell from being used until it is insta lled in a system. a pattern of 010 in bits 4 through 6 of register a turns the oscillator on and enable s the countdown chain. a pattern of 11x turns the oscillator on, but holds the countdown chain of the oscilla tor in reset. all other combinations of bits 4 through 6 keep the oscillator off. square-wave output selection thirteen of the 15 divider taps are made available to a 1-of-15 selector, as shown in the block diagram of figure 1. the first purpose of selecting a divider tap is to generate a square-wave output signal on the sqw pin. the rs0?rs3 bits in register a esta blish the square-wave output frequency. these frequencies are listed in table 1. the sqw frequency selection shares its 1?of?15 selector with the periodic interrupt generator. once the frequency is selected, the output of the sqw pin can be turned on and off under program control with the square-wave enable bit (sqwe). periodic interrupt selection the periodic interrupt causes the irq pin to go to an active state from once every 500ms to once every 122 s. this function is separate from the alarm in terrupt, which can be output from once per second to once per day. the periodic interrupt rate is selected using the same register a bits, which select the square-wave frequency (table 1). changing the regi ster a bits affect both the square-wave frequency and the periodic-interrupt output. howe ver, each function has a separate enable bit in register b. the sqwe bit controls the square-wave output. similarly, the periodic interrupt is enabled by the pie bit in register b. the periodic interrupt can be used with software counters to measure inputs, create output intervals, or await the next needed software function. update cycle the DS12887 executes an update cycle once per second re gardless of the set bit in register b. when the set bit in register b is set to 1, the user co py of the double-buffered time, calendar, and alarm bytes is frozen and will not update as the time incremen ts. however, the time countdown chain continues to update the internal copy of the buffer. this featur e allows time to maintain accuracy independent of reading or writing the time, calendar, and alarm buffers and also guarantees that time and calendar information is consistent. the update cycle also compares each alarm byte with the corresponding time byte and issues an alarm if a match or if a ? don?t care? code is present in all three positions. there are three methods that can handle access of the rtc that avoid any possibility of accessing inconsistent time and cale ndar data. the first method uses the update-ended interrupt. if enabled, an interrupt occurs after every update cycle that indi cates that over 999ms are available to read valid time and date information. if this interrupt is used, the irqf bit in register c should be cleared before leaving the interrupt routine. a second method uses the update-in-progress bit (uip) in register a to determine if the update cycle is in progress. the uip bit pulses once per second. after th e uip bit goes high, the update transfer occurs 244 s later. if a low is read on the uip bit, the user has at least 244 s before the time/calendar data is
DS12887 10 of 19 changed. therefore, the user should avoid interrupt se rvice routines that would cause the time needed to read valid time/calendar data to exceed 244 s. the third method uses a periodic interrupt to determin e if an update cycle is in progress. the uip bit in register a is set high between the setting of the pf bit in register c (figure 3). periodic interrupts that occur at a rate of greater than t buc allow valid time and date information to be reached at each occurrence of the periodic interrupt. the reads should be complete within one (t pi/2 + t buc ) to ensure that data is not read during the update cycle. figure 3. update-ended and per iodic interrupt relationship
DS12887 11 of 19 registers the DS12887 has four control registers that are acce ssible at all times, even during the update cycle. register a msb lsb bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 uip dv2 dv1 dv0 rs3 rs2 rs1 rs0 uip ? the update-in-progress (uip) bit is a status flag th at can be monitored. when the uip bit is a 1, the update transfer occurs soon. when uip is a 0, the updat e transfer does not occur for at least 244s. the time, calendar, and alarm information in ram is fully available for access when the uip bit is 0. the uip bit is read-only and is not affected by reset . writing the set bit in register b to a 1 inhibits any update transfer and clears the uip status bit. dv0, dv1, dv2? these three bits are used to turn the os cillator on or off and to reset the countdown chain. a pattern of 010 is the only combination of b its that turn the oscillator on and allow the rtc to keep time. a pattern of 11x enables the oscillator but holds the countdown chain in reset. the next update occurs at 500ms after a pattern of 010 is written to dv0, dv1, and dv2. rs3, rs2, rs1, rs0 ? these four rate-selection bits select one of the 13 taps on the 15-stage divider or disable the divider output. the tap se lected can be used to generate an output square-wave (sqw pin) and/or a periodic interrupt. the user can do one of the following: 1) enable the interrupt with the pie bit; 2) enable the sqw output pin with the sqwe bit; 3) enable both at the same time and the same rate; or 4) enable neither. table 1 lists the periodic interrupt rates and the square-wave frequencies that can be chosen with the rs bits. these four read/write bits are not affected by reset .
DS12887 12 of 19 register b msb lsb bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 set pie aie uie sqwe dm 24/12 dse set ? when the set bit is a 0, the update transfer func tions normally by advancing the counts once per second. when the set bit is written to a 1, any update transfer is inhibited a nd the program can initialize the time and calendar bytes without an update occurring in the midst of initializing. read cycles can be executed in a similar manner. set is a read/write bit that is not modified by reset or internal functions of the DS12887. pie ? the periodic-interrupt enable (pie) bit is a read/write bit that allows the periodic-interrupt flag (pf) bit in register c to drive the irq pin low. when the pie bit is set to 1, periodic interrupts are generated by driving the irq pin low at a rate specified by the rs3?rs0 bits of register a. a 0 in the pie bit blocks the irq output from being driven by a periodic in terrupt, but the periodic flag (pf) bit is still set at the periodic rate. pie is not modified by any internal DS12887 functions, but is cleared to 0 on reset . aie ? the alarm interrupt enable (aie) bit is a read/write bit that, when set to a 1, permits the alarm flag (af) bit in register c to assert irq . an alarm interrupt occurs for each second that the three time bytes equal the three alarm bytes, including a ?don?t ca re? alarm code of binary 11xxxxxx. when the aie bit is set to 0, the af bit does not initiate the irq signal. the reset pin clears aie to 0. the internal functions of the DS12887 do not affect the aie bit. uie ? the update-ended interrupt enable (uie) bit is a r ead/ write that enables the update-end flag (uf) bit in register c to assert irq . the reset pin going low or the set bit going high clears to uie bit. sqwe ? when the square-wave enable (sqwe) bit is set to a 1, a square-wave signal at the frequency set by the rate-selection bits rs3 through rs0 is dr iven out on a sqw pin. when the sqwe bit is set to z0, the sqw pin is held low; the state of sqwe is cleared by the reset pin. sqwe is a read/write bit. dm ? the data mode (dm) bit indicates whether time and calendar information is in binary or bcd format. the dm bit is set by the program to the approp riate format and can be read as required. this bit is not modified by internal functions or reset . a 1 in dm signifies binary data while a 0 in dm specifies bcd data. 24/12 ? the 24/12 control bit establishes the format of the hours byte. a 1 indicates the 24-hour mode and a 0 indicates the 12-hour mode. this bit is read/w rite and is not affected by internal functions of reset . dse ? the daylight savings enable (dse) bit is a re ad/write bit that enables two special updates when dse is set to 1. on the first sunday in april, the time increments from 1:59:59 am to 3:00:00 am. on the last sunday in october when the time first reaches 1:59:59 am, it changes to 1:00:00 am. these special updates do not occur when the dse bit is a 0. this bit is not affected by internal functions or reset .
DS12887 13 of 19 register c msb lsb bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 irqf pf af uf 0 0 0 0 irqf? the interrupt request flag (irqf) bit is set to a 1 when one or more of the following are true: pf = pie = 1 af = aie = 1 uf = uie = 1 that is, irqf = pf x pie + af x aie + uf x uie. any time the irqf bit is a 1, the irq pin is driven low. all flag bits are cleared after register c is read by the program or when the reset pin is low. pf? the periodic-interrupt flag (pf) is a read-only bit that is set to a 1 when an edge is detected on the selected tap of the divider chain. th e rs3 through rs0 bits establish the periodic rate. pf is set to a 1 independent of the state of the pie bit. when both pf and pie are 1s, the irq signal is active and sets the irqf bit. the pf bit is cleared by a reset or a software read of register c. af? a 1 in the alarm-interrupt flag (af) bit indicates that the current time has matched the alarm time. if the aie bit is also a 1, the irq pin goes low and a 1 appears in the irqf bit. a reset or a read of register c clears af. uf ? the update-ended interrupt flag (uf) bit is set after each update cycle. when the uie bit is set to 1, the one in uf causes the irqf bit to be a 1, which asserts the irq pin. uf is cleared by reading register c or a reset . bit 0, bit 1, bit 2, bit 3 ? these are unused bits of the status re gister c. these bits always read 0 and cannot be written. register d msb lsb bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 vrt0000000 vrt ? the valid ram and time (vrt) bit is set to the 1 state prior to shipment. this bit is not writable and should always be a 1 when read. if a 0 is ever pr esent, an exhausted internal lithium energy source is indicated and both the contents of the rtc data and ram data are questionable. this bit is unaffected by reset . bit 6, bit 5, bit 4, bit 3, bit 2, bit 1, bit 0? the remaining bits of register d are not usable. they cannot be written and, when read, they always read 0.
DS12887 14 of 19 absolute maximum ratings* voltage range on any pin rela tive to ground -0.3v to +7.0v operating temperature range 0 c to +70 c storage temperature range -40 c to +70 c soldering temperature see ipc/jedec j-std-020a (note 7) *this is a stress rating only and functional operation of the device at these or any other conditions beyond those indicated in the operation sections of this specification is not implied. exposure to absolute maximum rating conditions for extended periods of time can affect reliability. recommended dc operating conditions (t a = 0 c to +70 c) parameter symbol min typ max units notes power supply voltage v cc 4.5 5.0 5.5 v 1 input logic 1 v ih 2.2 v cc + 0.3 v 1 input logic 0 v il -0.3 0.8 v 1 dc electrical characteristics (v cc = 4.5 to 5.5v, 0 c to +70 c) parameter symbol min typ max units notes power supply current i cc1 715ma 2 input leakage i il -1.0 +1.0 a 3 i/o leakage i lo -1.0 +1.0 a 4 input current i mot -1.0 +500 a 3 output at 2.4v i oh -1.0 ma 1, 5 output at 0.4v i ol 4.0 ma 1 write protect voltage v tp 4.0 4.25 4.5 v capacitance (t a = +25 c) parameter symbol min typ max units notes input capacitance c in 5pf output capacitance c out 7pf
DS12887 15 of 19 ac electrical characteristics ( v cc = 4.5v to 5.5v, 0 c to +70 c) parameter symbol min typ max units notes cycle time t cyc 385 dc ns pulse width, ds/e low or rd/ wr high pw el 150 ns pulse width, ds/e high or rd/ wr low pw eh 125 ns input rise and fall time t r , t f 30 ns r/ w hold time t rwh 10 ns r/ w setup time before ds/e t rws 50 ns chip-select setup time before ds, wr , or rd t cs 20 ns chip-select hold time t ch 0ns read-data hold time t dhr 10 80 ns write-data hold time t dhw 0ns muxed address valid time to as/ale fall t asl 30 ns muxed address hold time t ahl 10 ns delay time ds/e to as/ale rise t asd 20 ns pulse width as/ale high pw ash 60 ns delay time, as/ale to ds/e rise t ased 40 ns output data delay time from ds/e or rd t ddr 20 120 ns 6 data setup time t dsw 100 ns reset pulse width t rwl 5 s irq release from ds t irds 2 s irq release from reset t irr 2 s notes: 1) all voltages are referenced to ground. 2) all outputs are open. 3) the mot pin has an internal pulldown of 20k . 4) applies to the ad0?ad7 pins, the irq pin, and the sqw pin when each is in the high-impedance state. 5) the irq pin is open drain. 6) measured with a load as shown in figure 4. 7) rtc modules can be successfully processed through conventional wave-soldering techniques as long as temperature exposure to the lithium energy source contained within does not exceed +85 c. however, post-solder cleaning with water-washing techniques is acceptable, provided that ultrasonic vibration is not used to prevent damage to the crystal.
DS12887 16 of 19 figure 4. output load figure 5. bus timing for motorola interface
DS12887 17 of 19 figure 6. bus timing for intel interface write cycle figure 7. bus timing for intel interface read cycle
DS12887 18 of 19 figure 8. irq release delay timing
DS12887 19 of 19 figure 9. power-up/down timing power-up/down timing parameter symbol min typ max units notes cs at v ih before power-down t pd 0 s v cc slew from 4.5v to 0v ( cs at v ih ) t f 300 s v cc slew from 0v to 4.5v ( cs at v ih ) t r 100 s cs at v ih after power-up t rec 20 200 ms ( t a = +25c ) parameter symbol min typ max units notes expected data retention t dr 10 years note: the rtc keeps time to an accuracy of 1 minute per month during data retention time for the period of t dr . warning: under no circumstances are negative undershoots, of any amplitude, allowed when device is in battery-backup mode.

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