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general description the DS12R885 is a functional drop-in replacement for the ds12885 real-time clock (rtc). the device pro- vides an rtc/calendar, one time-of-day alarm, three maskable interrupts with a common interrupt output, a programmable square wave, and 114 bytes of battery- backed static ram. the date at the end of the month is automatically adjusted for months with fewer than 31 days, including correction for leap years. it also oper- ates in either 24-hour or 12-hour format with an am/pm indicator. a precision temperature-compensated circuit monitors the status of v cc . if a primary power failure is detected, the device automatically switches to a back- up supply. the v backup pin supports a rechargeable battery or a super cap and includes an integrated, always enabled trickle charger. the DS12R885 is accessed through a multiplexed byte-wide interface, which supports both intel and motorola modes. the ds12cr887 and ds12r887 integrate the DS12R885 die with a crystal and battery. applications embedded systems utility meters security systems network hubs, bridges, and routers features ? trickle-charge capability for a rechargeable battery or super cap ? selectable intel or motorola bus timing ? rtc counts seconds, minutes, hours, day, date, month, and year with leap-year compensation to 2100 ? interrupt output with three independently maskable interrupt flags ? time-of-day alarm is once-per-second to once- per-day ? periodic rates from 122s to 500ms ? end-of-clock update cycle flag ? 14 bytes of clock and control registers ? 114 bytes of general-purpose ram with clear input ? programmable square-wave output ? automatic power-fail detect and switch circuitry ? +5.0v or +3.3v operation ? industrial temperature range ? ds12cr887 encapsulated dip (edip) module with integrated battery and crystal ? ds12r887 bga module surface-mountable package with integrated crystal and rechargeable battery DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger ______________________________________________ maxim integrated products 1 ordering information DS12R885 ds83c520 r/w as gnd x2 x1 v cc v cc crystal ds v backup super cap ad(0?) sqw reset irq rclr cs mot t ypical operating circuit rev 2; 12/04 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. part temp range pin- pa cka ge top mark DS12R885- 5 -40? to +85? 24 so (300 mils) DS12R885-5 DS12R885-33 -40? to +85? 24 so (300 mils) DS12R885-33 ds12cr887- 5 -40? to +85? 24 edip (700 mils) ds12cr887-5 d s 12c r 887- 33 -40? to +85? 24 edip (700 mils) ds12cr887-33 ds12r887- 5 -40? to +85? 48 bga ds12r887-5 ds12r887-33 -40? to +85? 48 bga ds12r887-33 pin configurations appear at end of data sheet.
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger 2 _____________________________________________________________________ absolute maximum ratings 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 operating temperature range ...........................-40? to +85? storage temperature range .............................-55? to +125? soldering temperature .......................................see ipc/jedec j-std-020a specification soldering temperature (leads, 10s) ................................+260? 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 -33 2.97 3.3 3.63 supply voltage (note 2) v cc -5 4.5 5.0 5.5 v v backup input voltage (DS12R885 only) v backup (note 2) 2.0 v out v input logic 1 v ih (note 2) 2.2 v cc + 0.3 v input logic 0 v il (note 2) -0.3 +0.8 v -33 0.7 2 v cc power-supply current (note 3) i cc1 -5 0.8 2 ma -5 0.250 0.5 v cc standby current (note 4) i ccs -33 0.140 0.3 ma input leakage i il -1.0 +1.0 ? i/o leakage i ol (note 5) -1.0 +1.0 ? input current i mot (note 6) -1.0 +500 ? output current at 2.4v i oh (note 2) -1.0 ma output current at 0.4v i ol (note 2) 4.0 ma -33 2.7 2.88 2.97 power-fail voltage (note 2) v pf -5 4.05 4.33 4.5 v -33 vrt trip point vrt trip -5 1.3 v trickle-charger current-limiting resistor r1 DS12R885 only 10 k ? trickle-charger output voltage v out DS12R885 only 3.05 v
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger _____________________________________________________________________ 3 dc electrical characteristics (DS12R885 only) ( v cc = 0v, v backup = 3.2v , t a = -40? to +85?, unless otherwise noted.) (note 1) parameter symbol conditions min typ max units v backup current (osc on); t a = +25?, v backup = 3.0v i backup2 (note 7) 800 1000 na v backup current (oscillator off) i backupdr (note 7) 100 na ac electrical characteristics ( v cc = 4.5v to 5.5v , t a = -40? to +85?.) (note 1) parameter symbol conditions min typ max units cycle time t cyc 180 dc ns pulse width, ds low or r/ w high pw el 80 ns pulse width, ds high or r/ w low pw eh 65 ns input rise and fall t r , t f 30 ns r/ w hold time t rwh 0ns r/ w setup time before ds/e t rws 10 ns chip-select setup time before ds or r/ w t cs 5ns chip-select hold time t ch 0ns read-data hold time t dhr 535ns write-data hold time t dhw 0ns address valid time to as fall t asl 20 ns address hold time to as fall t ahl 5ns delay time ds/e to as rise t asd 10 ns pulse width as high pw ash 30 ns delay time, as to ds/e rise t ased 35 ns output data delay time from ds or r/ w t ddr (note 8) 15 60 ns data setup time t dsw 50 ns reset pulse width t rwl 5s irq release from ds t irds 02s irq release from reset t irr 02s
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger 4 _____________________________________________________________________ ac electrical characteristics (v cc = 2.97v to 3.63v , t a = -40? to +85?.) (note 1) parameter symbol conditions min typ max units cycle time t cyc 280 dc ns pulse width, ds low or r/ w high pw el 130 ns pulse width, ds high or r/ w low pw eh 90 ns input rise and fall t r , t f 30 ns r/ w hold time t rwh 0ns r/ w setup time before ds t rws 15 ns chip-select setup time before ds or r/ w t cs 8ns chip-select hold time t ch 0ns read-data hold time t dhr 555ns write-data hold time t dhw 0ns address valid time to as fall t asl 30 ns address hold time to as fall t ahl 15 ns delay time ds to as rise t asd 15 ns pulse width as high pw ash 45 ns delay time, as to ds rise t ased 55 ns output data delay time from ds or r/ w t ddr (note 8) 20 80 ns data setup time t dsw 70 ns reset pulse width t rwl 5s irq release from ds t irds 02s irq release from reset t irr 02s
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger _____________________________________________________________________ 5 pw ash pw el t ased t cyc t rws t cs t rwh t ch pw eh t asd ad0?d7 read cs r/ w as ds ad0?d7 write t dhw t dhr t ddr t ahl t asl t dsw motorola bus read/write timing intel bus write timing pw ash pw asl pw eh t cs t ahl t asl t dsw t dhw t ch t asd t asd t cyc cs r/w as ds ad0?d7 write
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger 6 _____________________________________________________________________ t cs t ahl t asl t cyc pw ash pw asl pw eh cs r/w as ds ad0?d7 t asd t asd t ased t ddr t dhr t ch intel bus read timing t irds t irds t irds ds reset irq irq release delay timing outputs inputs high-z don't care v alid recognized recognized v alid v cc t f v pf(max) v pf(min) t rpu t r power-up/power-down timing
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger _____________________________________________________________________ 7 power-up/power-down characteristics (t a = -40? to +85?) (note 1) parameter symbol conditions min typ max units recovery at power-up t rpu 20 200 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 capacitance (t a = +25?) parameter symbol conditions min typ max units capacitance on all input pins except x1 and x2 c in (note 9) 10 pf capacitance on irq , sqw, and dq pins c io (note 9) 10 pf ac test conditions parameter test conditions input pulse levels (-5) 0 to 3.0v input pulse levels (-33) 0 to 2.7v output load including scope and jig (-5) 50pf + 1ttl gate output load including scope and jig (-33) 25pf + 1ttl gate input and output timing measurement reference levels input/output: v il maximum and v ih minimum input-pulse rise and fall times 5ns warning: negative undershoots below -0.3v while the part is in battery-backed mode may cause loss of data. note 1: limits at -40? are guaranteed by design and not production tested. note 2: all voltages are referenced to ground. note 3: all outputs are open. note 4: specified with cs = ds = r/ w = reset = v cc ; mot, as, ad0?d7 = 0; v backup open. note 5: applies to the ad0 to ad7 pins, the irq pin, and the sqw pin when each is in a high-impedance state. note 6: the mot pin has an internal 20k ? pulldown. note 7: measured with a 32.768khz crystal attached to x1 and x2. note 8: measured with a 50pf capacitance load. note 9: guaranteed by design. not production tested.
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger 8 _____________________________________________________________________ t ypical operating characteristics (v cc = +3.3v, t a = +25?, unless otherwise noted.) oscillator frequency vs. supply voltage DS12R885 toc04 supply (v) frequency (hz) 5.0 4.5 3.5 4.0 3.0 2.5 32767.92 32767.94 32767.96 32767.98 32768.00 32768.02 32768.04 32768.06 32768.08 32768.10 32767.90 2.0 5.5 i backup vs. temperature (DS12R885) DS12R885 toc03 temperature ( c) supply current (na) 65 50 -25 -10 5 20 35 475 500 525 550 575 600 625 650 450 -40 80 v cc = 0v, v backup = 3.0v v backup vs. v cc vs. i backup (DS12R885) DS12R885 toc02 v cc v backup 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 2.2 2.4 2.6 2.8 3.0 2.0 1.0 5.5 0 a -15 a -30 a -45 a -60 a i backup vs. v backup (DS12R885) DS12R885 toc01 v backup (v) supply current (na) 2.8 2.5 2.3 575 600 625 550 2.0 3.0 v cc = 0v
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger _____________________________________________________________________ 9 power control and trickle charger v backup osc bus interface v cc x1 x2 ds12r887/ ds12cr887 only ds12r887/ ds12cr887 only reset cs ds as r/w mot ad0?d7 divide by 8 divide by 64 divide by 64 16:1 mux square- wave generator registers a, b, c, d clock/calendar and alarm registers user ram 114 bytes clock/calendar update logic irq sqw irq generator buffered clock/ calendar and alarm registers gnd rlcr DS12R885 functional diagram pin description pin so edip bga name function 11c5 mot motorola or intel bus timing selector. this pin selects one of two bus types. when connected to v cc , motorola bus timing is selected. when connected to gnd or left disconnected, intel bus timing is selected. the pin has an internal pulldown resistor. 2x1 3x2 connections for standard 32.768khz quartz crystal. the internal oscillator circuitry is designed for operation with a crystal having a 12.5pf specified load capacitance (c l ). 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. 4?1 4?1 f4, d4, f3, d3, f2, d2, f1, d1 ad0 ad7 multiplexed, bidirectional address/data bus. the addresses are presented during the first portion of the bus cycle and latched into the DS12R885 by the falling edge of as. write data is latched by the falling edge of ds (motorola timing) or the rising edge of r/ w (intel timing). in a read cycle, the DS12R885 outputs data during the latter portion of ds (ds and r/ w high for motorola timing, ds low and r/ w high for intel timing). the read cycle is terminated and the bus returns to a high-impedance state as ds transitions low in the case of motorola timing or as ds transitions high in the case of intel timing.
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger 10 ____________________________________________________________________ pin description (continued) pin so edip bga name function 12 12 d5?8, e1?8, f5?8 gnd ground 13 13 c1 cs chip-select input. the active-low chip-select signal must be asserted low for a bus cycle in the DS12R885 to be accessed. cs must be kept in the active state during ds and as for motorola timing and during ds and r/ w for intel timing. bus cycles that take place without asserting cs latch addresses, but no access occurs. when v cc is below v pf volts, the DS12R885 inhibits access by internally disabling the cs input. this action protects the rtc data and the ram data during power outages. 14 14 c3 as address strobe input. a positive-going address-strobe pulse serves to demultiplex the bus. the falling edge of as causes the address to be latched within the DS12R885. the next rising edge that occurs on the as bus clears the address regardless of whether cs is asserted. an address strobe must immediately precede each write or read access. if a write or read is performed with cs deasserted, another address strobe must be performed prior to a read or write access with cs asserted. 15 15 c2 r/ w read/write input. the r/ w pin 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. in this mode, the r/ w pin operates in a similar fashion as the write-enable signal ( we ) on generic rams. data are latched on the rising edge of the signal. 16, 22 2, 3, 16, 20?2 a3 n.c. no connection. this pin should remain unconnected. on the edip, these pins are missing by design. 17 17 a1 ds d ata s tr ob e or read inp ut. th e d s p i n has tw o m od es of op er ati on d ep end i ng on the l evel of the m ot p i n. when the m o t p i n i s co nnected to v c c , m otor ol a b us ti m i ng i s sel ected . in thi s m od e, d s i s a p osi ti ve p ul se d ur i ng the l a tter p or ti on of the b us cycl e and i s cal l ed d ata str ob e. d ur i ng r ead cycl es, d s si g ni fi es the ti m e that the d s 12r885 i s to d r i ve the b i d i r ecti onal b us. in w r i te cy cl es, th e tr ai l i ng ed g e of d s causes the d s 12r885 to l atch the w r i tten d ata. w hen the m o t p i n i s c onnected to g n d , intel b us ti m i ng i s sel ected . d s i d enti fi es the ti m e p er i od w hen the d s 12r885 d r i ves the b us w i th r ead d ata. in thi s m od e, the d s p i n op er ates i n a si m i l ar fashi on as the outp ut- enab l e ( o e ) si g nal on a g ener i c ram .
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger ____________________________________________________________________ 11 pin description (continued) pin so edip bga name function 18 18 a2 reset reset input. the reset pin has no effect on the clock, calendar, 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 reset is low should exceed 200ms to ensure that the internal timer that controls the DS12R885 on power-up has timed out. when reset is low and v cc is above v pf , the following occurs: a. periodic interrupt-enable (pie) bit is cleared to 0. b. alarm interrupt-enable (aie) bit is cleared to 0. c. update-ended interrupt-enable (uie) bit is cleared to 0. d. periodic-interrupt flag (pf) bit is cleared to 0. e. alarm-interrupt flag (af) bit is cleared to 0. f. update-ended interrupt flag (uf) bit is cleared to 0. g. interrupt-request status flag (irqf) bit is cleared to 0. h. irq pin is in the high-impedance state. i. the device is not accessible until reset is returned high. j. square-wave output-enable (sqwe) bit is cleared to 0. in a typical application, reset can be connected to v cc . this connection allows the DS12R885 to go in and out of power fail without affecting any of the control registers. 19 19 a4 irq interrupt request output. the irq pin is an active-low output of the DS12R885 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 interrupt-enable bit is set. the processor program normally reads the c register to clear the irq pin. 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, provided that they are all open drain. the irq pin is an open-drain output and requires an external pullup resistor to v cc . 20 v backup connection for rechargeable battery or super cap. this pin provides trickle charging when v cc is greater than v backup . 21 a5 rclr ram clear. the active-low rclr pin is used to clear (set to logic 1) all 114 bytes of general-purpose ram, but does not affect the ram associated with the rtc. to clear the ram, rclr must be forced to an input logic 0 during battery-backup mode when v cc is not applied. the rclr function is designed to be used through a human interface (shorting to ground manually or by a switch) and not to be driven with external buffers. this pin is internally pulled up. do not use an external pullup resistor on this pin. 23 23 c4 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 v pf . 24 24 a6?8, b1?8, c6?8 v cc dc power pin for primary power supply. when v cc is applied within normal limits, the device is fully accessible and data can be written and read. when v cc is below v pf reads and writes are inhibited.
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger 12 ____________________________________________________________________ detailed description the DS12R885 is a drop-in replacement for the ds12885 rtc. the device provides 14 bytes of real- time clock/calendar, alarm, and control/status registers and 114 bytes of nonvolatile, battery-backed static ram. a time-of-day alarm, three maskable interrupts with a common interrupt output, and a programmable square-wave output are available. the DS12R885 also operates in either 24-hour or 12-hour format with an am/pm indicator. a precision temperature-compensat- ed circuit monitors the status of v cc . if a primary power-supply failure is detected, the device automati- cally switches to a backup supply. the backup supply input supports either a rechargeable battery or a super cap, and includes an integrated trickle charger. the trickle charger is always enabled. the DS12R885 is accessed through a multiplexed address/data bus that supports intel and motorola modes. the ds12r887 is a surface-mount package using the DS12R885 die, a 32.768khz crystal, and a recharge- able battery. the device provides a real-time clock/cal- endar, one time-of-day alarm, three maskable interrupts with a common interrupt output, a programmable square wave, and 114 bytes of nonvolatile, battery- backed static ram. the date at the end of the month is automatically adjusted for months with fewer than 31 days, including correction for leap years. it also oper- ates in either 24-hour or 12-hour format with an am/pm indicator. a precision temperature-compensated circuit monitors the status of v cc . if a primary power failure is detected, the device automatically switches to a back- up battery included in the package. the device is accessed through a multiplexed byte-wide interface, which supports both intel and motorola modes. the ds12cr887 edip integrates a DS12R885 die with a crystal and battery. the charging circuit on the DS12R885 die is disabled. the battery has sufficient capacity to power the oscillator and registers for five years in the absence of v cc at +25?. the ds12r887 bga includes a crystal and a recharge- able battery. a fully charged battery can power the oscil- lator and registers (typical current at +25?) in the absence of v cc for approximately 11 days (10% of capacity consumed) or 98 days (90% capacity con- sumed). when the discharge depth is 10% of capacity, the battery can be recharged up to 1,000 times. if the dis- charge depth is 90% of capacity, the battery can be recharged up to 30 times. thus, the life of the device would be approximately 30 years (11 days x 1,000 cycles) or 8 years (98 days x 30 cycles). charging time to full capacity is approximately two days with v cc applied. please consult related application notes for detailed information on battery lifetime versus depth of dis- charge, and expected product lifetime based upon battery cycles. oscillator circuit the DS12R885 uses an external 32.768khz crystal. the oscillator circuit does not require any external resistors or capacitors to operate. table 1 specifies several crys- tal parameters for the external crystal. figure 1 shows a functional schematic of the oscillator circuit. an enable bit in the control register controls the oscillator. oscillator startup times are highly dependent upon crystal characteristics, pc board leakage, and layout. high esr and excessive capacitive loads are the major contributors to long startup times. a circuit using a crystal with the recommended characteristics and proper layout usually starts within one second. an external 32.768khz oscillator can also drive the DS12R885. in this configuration, the x1 pin is connected to the external oscillator signal and the x2 pin is floated. countdown chain x1 x2 crystal c l 1c l 2 r tc registers DS12R885 figure 1. oscillator circuit showing internal bias network parameter symbol min typ max units nominal frequency f o 32.768 khz series resistance esr 50 k ? load capacitance c l 12.5 pf table 1. crystal specifications* * 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 additional specifications.
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger ____________________________________________________________________ 13 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 cou- pled into the oscillator circuit can result in the clock run- ning fast. figure 2 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 clocks for more detailed information. the ds12r887 and ds12cr887 are calibrated at the factory to an accuracy of ? minute per month at +25? during data-retention time for the period t or . power-down/power-up considerations the real-time clock continues to operate regardless of the v cc input level, and the ram and alarm memory locations remain nonvolatile. v backup must remain within the minimum and maximum limits when v cc is not applied. when v cc is applied and exceeds v pf (power-fail trip point), the device becomes accessible after t rec ?f the oscillator is running and the oscillator countdown chain is not in reset (register a). this time allows the system to stablize after power is applied. if the oscillator is not enabled, the oscillator-enable bit is enabled on power-up, and the device becomes imme- diately accessible. time, calendar, and alarm locations the time and calendar information is obtained by read- ing the appropriate register bytes. the time, calendar, and alarm are set or initialized by writing the appropri- ate register bytes. the contents of the 10 time, calen- dar, and alarm bytes can be either binary or binary-coded decimal (bcd) format. the day-of-week register increments at midnight, incre- menting from 1 through 7. the day-of-week register is used by the daylight savings function, so the value 1 is defined as sunday. the date at the end of the month is automatically adjusted for months with fewer than 31 days, including correction for leap years. before writing the internal time, calendar, and alarm reg- isters, the set bit in register b should be written to logic 1 to prevent updates from occurring while access is being attempted. in addition to writing the 10 time, calen- dar, 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 bit in register b should be cleared after the data mode bit has been written to allow the rtc to update the time and calendar bytes. once initialized, the rtc makes all updates in the selected mode. the data mode cannot be changed without reinitializing the 10 data bytes. tables 2a and 2b show the bcd and binary formats of the time, calendar, and alarm locations. the 24-12 bit cannot be changed without reinitializing the hour locations. when the 12-hour format is selected, the higher-order bit of the hours byte represents pm when it is logic 1. the time, calendar, and alarm bytes are always accessible because they are double-buffered. once per second the seven bytes are advanced by one 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., may not correlate. the probability of read- ing incorrect time and calendar data is low. several methods of avoiding any possible incorrect time and calendar reads are covered later in this text. 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 2. layout example
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger 14 ____________________________________________________________________ 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 inter- rupt is initiated at the specified time each day, if the alarm-enable bit is high. in this mode, the ??bits in the alarm registers and the corresponding time registers must always be written to 0 ( table 2a and 2b). writing the 0 bits in the alarm and/or time registers to 1 can result in undefined operation. the second use condition is to insert a ?on? care state in one or more of the three alarm bytes. the don?- care code is any hexadecimal value from c0 to ff. the two most significant bits of each byte set the don?-care condition when at logic 1. an alarm is generated each hour when the don?-care bits are set in the hours byte. similarly, an alarm is generated every minute with don?-care codes in the hours and minute alarm bytes. the don?-care codes in all three alarm bytes create an interrupt every second. all 128 bytes can be directly 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 msb of the seconds byte is read-only. table 2a. time, calendar, and alarm data modes?bcd mode (dm = 0) address bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 function range 00h 0 10 seconds seconds seconds 00?9 01h 0 10 seconds seconds seconds alarm 00?9 02h 0 10 minutes minutes minutes 00?9 03h 0 10 minutes minutes minutes alarm 00?9 am/pm 0 10 hours 04h 0 0 10 hours hours hours 1?2 +am/pm 00?3 am/pm 0 10 hours 05h 0 0 10 hours hours hours alarm 1?2 +am/pm 00?3 06h 0 0 0 0 0 day day 01?7 07h 0 0 10 date date date 01?1 08h 0 0 0 10 months month month 01?2 09h 10 years year year 00?9 0ah uip dv2 dv1 dv0 rs3 rs2 rs1 rs0 control 0bh set pie aie uie sqwe dm 24/12 dse control 0ch irqf pf af uf 0 0 0 0 control 0dh vrt 0 0 0 0 0 0 0 control 0eh-7f x x x x x x x x ram x = read/write bit. note: unless otherwise specified, the state of the registers is not defined when power is first applied. except for the seconds regis - ter, 0 bits in the time and date registers can be written to 1, but may be modified when the clock updates. 0 bits should alway s be written to 0 except for alarm mask bits.
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger ____________________________________________________________________ 15 table 2b. time, calendar, and alarm data modes?binary mode (dm = 1) address bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 function range 00h 0 0 seconds seconds 00?b 01h 0 0 seconds seconds alarm 00?b 02h 0 0 minutes minutes 00?b 03h 0 0 minutes minutes alarm 00?b am/pm 0 hours 04h 0 00 hours hours 01?c +am/pm 00?7 am/pm 0 hours 05h 0 0 0 hours hours alarm 01?c +am/pm 00?7 06h 0 0 0 0 0 day day 01?7 07h 0 0 0 date date 01?f 08h 0 0 0 0 month month 01?c 09h 0 year year 00?3 0ah uip dv2 dv1 dv0 rs3 rs2 rs1 rs0 control 0bh set pie aie uie sqwe dm 24/12 dse control 0ch irqf pf af uf 0 0 0 0 control 0dh vrt 0 0 0 0 0 0 0 control 0eh-7f x x x x x x x x ram x = read/write bit. note: unless otherwise specified, the state of the registers is not defined when power is first applied. except for the seconds regis - ter, 0 bits in the time and date registers can be written to 1, but may be modified when the clock updates. 0 bits should alway s be written to 0 except for alarm mask bits.
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger 16 ____________________________________________________________________ bit 7: update-in-progress (uip). this bit is a status flag that can be monitored. when the uip bit is a 1, the update transfer occurs soon. when uip is a 0, the update transfer does not occur for at least 244?. 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. bits 6, 5, and 4: dv2, dv1, dv0. these three bits are used to turn the oscillator on or off and to reset the countdown chain. a pattern of 010 is the only combina- tion of bits 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. bits 3 to 0: rate selector (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 selected 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 3 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 . bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 uip dv2 dv1 dv0 rs3 rs2 rs1 rs0 control register a control registers the DS12R885 has four control registers that are accessible at all times, even during the update cycle.
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger ____________________________________________________________________ 17 bit 7: set. when the set bit is 0, the update transfer functions normally by advancing the counts once per second. when the set bit is written to 1, any update transfer is inhibited, and 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 and is not affected by reset or internal functions of the DS12R885. bit 6: periodic interrupt enable (pie). the 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?s0 bits of register a. a 0 in the pie bit blocks the irq output from being driven by a periodic interrupt, but the pf bit is still set at the periodic rate. pie is not modified by any internal DS12R885 functions, but is cleared to 0 on reset . bit 5: alarm interrupt enable (aie). this bit is a read/write bit that, when set to 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?-care alarm code of binary 11xxxxxx. the af bit does not initiate the irq signal when the aie bit is set to 0. the internal functions of the DS12R885 do not affect the aie bit, but is cleared to 0 on reset . bit 4: update-ended interrupt enable (uie). this bit is a read/write bit 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 the uie bit. uie is not modified by any internal DS12R885 functions, but is cleared to 0 on reset . bit 3: square-wave enable (sqwe). when this bit is set to 1, a square-wave signal at the frequency set by the rate-selection bits rs3?s0 is driven out on the sqw pin. when the sqwe bit is set to 0, the sqw pin is held low. sqwe is a read/write bit and is cleared by reset . sqwe is low if disabled, and is high imped- ance when v cc is below v pf . sqwe is cleared to 0 on reset . bit 2: data mode (dm). this bit indicates whether time and calendar information is in binary or bcd format. the dm bit is set by the program to the appropriate for- mat and can be read as required. this bit is not modi- fied by internal functions or reset . a 1 in dm signifies binary data, while a 0 in dm specifies bcd data. bit 1: 24/12. the 24/12 control bit establishes the for- mat of the hours byte. a 1 indicates the 24-hour mode and a 0 indicates the 12-hour mode. this bit is read/write and is not affected by internal functions or reset . bit 0: daylight savings enable (dse). this bit is a read/write bit that enables two daylight savings adjust- ments 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. when dse is enabled, the internal logic tests for the first/last sunday condition at midnight. if the dse bit is not set when the test occurs, the daylight savings function does not operate correctly. these adjustments do not occur when the dse bit is 0. this bit is not affected by internal functions or reset . 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 control register b
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger 18 ____________________________________________________________________ bit 7: interrupt request flag (irqf). this bit is set to 1 when any of the following are true: pf = pie = 1 af = aie = 1 uf = uie = 1 any time the irqf bit is 1, the irq pin is driven low. this bit can be cleared by reading register c or with a reset . bit 6: periodic interrupt flag (pf). this bit is read- only and is set to 1 when an edge is detected on the selected tap of the divider chain. the rs3 through rs0 bits establish the periodic rate. pf is set to 1 indepen- dent of the state of the pie bit. when both pf and pie are 1s, the irq signal is active and sets the irqf bit. this bit can be cleared by reading register c or with a reset . bit 5: alarm interrupt flag (af). a 1 in the af bit indi- cates that the current time has matched the alarm time. if the aie bit is also 1, the irq pin goes low and a 1 appears in the irqf bit. this bit can be cleared by reading register c or with a reset . bit 5: update-ended interrupt flag (uf). this bit is set after each update cycle. when the uie bit is set to 1, the 1 in uf causes the irqf bit to be a 1, which asserts the irq pin. this bit can be cleared by reading register c or with a reset . bits 3 to 0: unused. these bits are unused in register c. these bits always read 0 and cannot be written. bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 i rqf pf af uf 0000 control register c bit 7 bit 6 bit 5 bit 4 bit 3 bit 2 bit 1 bit 0 vrt 0000000 control register d bit 7: valid ram and time (vrt). this bit indicates the condition of the battery connected to the v backup pin. this bit is not writeable and should always be 1 when read. if a 0 is ever present, an exhausted internal lithium energy source is indicated and both the con- tents of the rtc data and ram data are questionable. this bit is unaffected by reset . bits 6 to 0: unused. the remaining bits of register d are not usable. they cannot be written and they always read 0.
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger ____________________________________________________________________ 19 nonvolatile ram (nv ram) the 114 general-purpose nv ram bytes are not dedi- cated to any special function within the DS12R885. they can be used by the processor program as battery-backed memory and are fully available during the update cycle. interrupts the DS12R885 includes three separate, fully automatic 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?. the update- ended interrupt can be used to indicate to the program that an update cycle is complete. each of these inde- pendent interrupt conditions is described in greater detail in other sections of this text. the processor program can select which interrupts, if any, are 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 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 inde- pendent of the state of the corresponding 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 interro- gate as necessary. when a flag is set, an indication is given to software that an interrupt event has occurred since the flag bit was last read; however, care should be taken when using the flag bits as they are cleared each time register c is read. double latching is includ- ed with register c so that bits that are set remain sta- ble 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 register c is read to ensure that no interrupts are lost. the second flag bit method is used with fully enabled interrupts. when an interrupt flag bit is set and the cor- responding 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 set. the irqf bit in register c is a 1 whenever the irq pin is driven low. determination that the rtc initiat- ed 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 DS12R885. the act of reading register c clears all active flag bits and the irqf bit. oscillator control bits when the ds12r887 and ds12cr887 are shipped from the factory, the internal oscillator is turned off. this feature prevents the lithium energy cell from being used until it is installed in a system. a pattern of 010 in bits 4 to 6 of register a turns the oscillator on and enables the countdown chain. a pat- tern of 11x (dv2 = 1, dv1 = 1, dv0 = x) turns the oscil- lator on, but holds the countdown chain of the oscillator in reset. all other combinations of bits 4 to 6 keep the oscillator off. square-wave output selection thirteen of the 15 divider taps are made available to a 1- of-16 multiplexer, as shown in the functional diagram. the square-wave and periodic-interrupt generators share the output of the multiplexer. the rs0?s3 bits in register a establish the output frequency of the multi- plexer (see table 1). 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?. this function is separate from the alarm inter- rupt, which can be output from once per second to once per day. the periodic interrupt rate is selected using the same register a bits that select the square- wave frequency ( table 1). changing the register a bits affects the square-wave frequency and the periodic- interrupt output. however, each function has a separate enable bit in register b. the sqwe bit controls the square-wave output. similarly, the pie bit in register b enables the periodic interrupt. the periodic interrupt can be used with software counters to measure inputs, create output intervals, or await the next needed soft- ware function.
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger 20 ____________________________________________________________________ update cycle the DS12R885 executes an update cycle once per second regardless of the set bit in register b. when the set bit in register b is set to 1, the user copy of the double-buffered time, calendar, and alarm bytes is frozen and does not update as the time increments. however, the time countdown chain continues to update the internal copy of the buffer. this feature allows time to maintain accuracy independent of read- ing 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?-care code is present in all three positions. there are three methods that can handle rtc access that avoid any possibility of accessing inconsistent time and calendar data. the first method uses the update- ended interrupt. if enabled, an interrupt occurs after every update cycle that indicates over 999ms is avail- able 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 the uip bit goes high, the update transfer occurs 244? later. if a low is read on the uip bit, the user has at least 244? before the time/calendar data is changed. therefore, the user should avoid interrupt service rou- tines that would cause the time needed to read valid time/calendar data to exceed 244?. the third method uses a periodic interrupt to determine 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 greater than t buc allow valid time and date infor- mation to be reached at each occurrence of the period- ic interrupt. the reads should be complete within 1(t pi/2 + t buc ) to ensure that data is not read during the update cycle. select bits register a rs3 rs2 rs1 rs0 t pi periodic interrupt rate sqw output frequency 00 00 none none 0001 3.90625ms 256hz 00 10 7.8125ms 128hz 0011 122.070? 8.192khz 0100 244.141? 4.096khz 0101 488.281? 2.048khz 0110 976.5625? 1.024khz 0111 1.953125ms 512hz 1000 3.90625ms 256hz 10 01 7.8125ms 128hz 10 10 15.625ms 64hz 10 11 31.25ms 32hz 11 00 62.5ms 16hz 11 01 125ms 8hz 11 10 250ms 4hz 11 11 500ms 2hz table 3. periodic interrupt rate and square-wave output frequency uip uf pf t buc = delay time before update cycle = 244 s 1 second t pi t p1/2 t p1/2 t buc figure 3. uip and periodic interrupt timing
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger ____________________________________________________________________ 21 handling, pc board layout, and assembly the edip and bga packages contain a quartz tuning- fork crystal. pick-and-place equipment can be used, but precautions should be taken to ensure that exces- sive shocks are avoided. ultrasonic cleaning should be avoided to prevent damage to the crystal. the bga package can be reflowed as long as the fol- lowing conditions are met: 1. preheating (below 160?) is within 90 seconds. 2. maximum time above 150? is less than 180 seconds. 3. maximum time above 170? is less than 100 seconds. 4. maximum time above 200? is less than 60 seconds. 5. maximum time above 220? is less than 30 seconds. 6. peak temperature is less than or equal to 230?. exposure to reflow is limited to two times maximum. moisture-sensitive packages are shipped from the factory dry-packed. handling instructions listed on the package label must be followed to prevent damage dur- ing reflow. refer to the ipc/jedec j-std-020b standard for moisture-sensitive device (msd) classifications. 24 23 22 21 20 19 18 17 1 2 3 4 5 6 7 8 v cc sqw n.c. rclr ad0 x2 x1 mot top view v backup irq reset ds ad4 ad3 ad2 ad1 16 15 14 13 9 10 11 12 n.c. r/w as cs gnd ad7 ad6 ad5 so (0.300") DS12R885 24 23 22 21 20 19 18 17 1 2 3 4 5 6 7 8 v cc sqw n.c. n.c. ad0 n.c. n.c. mot n.c. irq reset ds ad4 ad3 ad2 ad1 16 15 14 13 9 10 11 12 n.c. r/w as cs gnd ad7 ad6 ad5 edip (0.700") ds12cr887 pin configurations
DS12R885/ds12cr887/ds12r887 r tc with constant-voltage trickle charger package information for the latest package outline information, go to www.maxim-ic.com/dallaspackinfo . package theta-ja (?/w) theta-jc (?/w) so 105 22 thermal information chip information transistor count: 17,061 process: cmos substrate connected to ground v cc cs ad7 ds a 1 2 3 4 bc d 5 6 gnd ad6 ef reset v cc r/w ad5 gnd ad4 v cc as ad3 n.c. gnd ad2 irq v cc sqw ad1 gnd ad0 v cc mot gnd rclr gnd gnd v cc v cc v cc gnd gnd gnd 7 v cc v cc v cc gnd gnd gnd 8 v cc v cc v cc gnd gnd gnd 48 bga ds12r887 top view (bump side down) pin configurations (continued) 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. 22 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2004 maxim integrated products printed usa is a registered trademark of maxim integrated products. is a registered trademark of dallas semiconductor corporation.

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