1 of 4 092600 features incorporates industry standard ds1287 pc clock plus enhanced features: +3 or +5v operation 64?bit silicon serial number 64?bit customer specific rom or additional serial number available power control circuitry supports system power on from date/time alarm or key closure automatic battery backup and write protection to external sram crystal select bit allows rtc to operate with 6 pf or 12.5 pf crystal 114 bytes user nv ram auxiliary battery input ram clear input century register 32 khz output for power management 32?bit v cc powered elapsed time counter 32?bit v bat powered elapsed time counter 16?bit power cycle counter compatible with existing bios for original ds1287 functions available as ic (ds1688) or stand?alone module with embedded battery and crystal (DS1691) timekeeping algorithm includes leap year compensation valid up to 2100 ordering information part # description ds1688s rtc ic, 28?pin soic DS1691 rtc module; 28?pin dip pin assignment pin description x1 - crystal input x2 - crystal output rclr - ram clear input ad0-ad7 - mux?ed address/data bus pwr - power-on interrupt output ks - kickstart input cs - rtc chip select input ale - rtc address strobe wr - rtc write data strobe rd - rtc read data strobe v cco - ram power supply output ds1688/DS1691 3 volt/5 volt serialized real time clock with nv ram control www.dalsemi.com
ds1688/DS1691 2 of 4 irq - interrupt request output sqw - square wave output v cci - +3 or +5v main supply gnd - ground v bat - battery + supply v baux - auxiliary battery supply psel - +3 or +5v power select cei - ram chip enable in ceo - ram chip enable out description the ds1688/DS1691 is a real time clock (rtc) designed as a successor to the industry standard ds1285, ds1385, ds1485, and ds1585 pc real time clocks. this device provides the industry standard ds1285 clock function with the new feature of either +3.0 or +5.0 volt operation and automatic backup and write protection to an external sram. the ds1688 also incorporates a number of enhanced features including a silicon serial number, power on/off control circuitry, 114 bytes of user nv sram, power on elapsed timer, and power cycle counter. each ds1688/DS1691 is individually manufactured with a unique 64?bit serial number as well as an additional 64?bit customer specific rom or serial number. the serial number is programmed and tested at dallas to insure that no two devices are alike. the serial number can be used to electronically identify a system for purposes such as establishment of a network node address or for maintenance tracking. blocks of available numbers from dallas semiconductor can be reserved by the customer. the serialized rtc?s also incorporate power control circuitry, which allows the system to be powered on via an external stimulus, such as a keyboard or by a time and date (wake up) alarm. the pwr output pin can be triggered by one or either of these events, and can be used to turn on an external power supply. the pwr pin is under software control, so that when a task is complete, the system power can then be shut down. the ds1688/DS1691 incorporates a power on elapsed time counter, a power on cycle counter, and a battery powered continuous counter. these three counters provide valuable information for maintenance and warranty requirements. automatic backup and write protection for an external sram is provided through the v cco and ceo pins. the lithium energy source used to permanently power the real time clock is also used to retain ram data in the absence of v cc power through the v cco pin. the chip enable out-put to ram ( ceo ) is controlled during power transients to prevent data corruption. the ds1688 is a clock/calendar chip with the features described above. an external crystal and battery are the only components required to maintain time?of?day and memory status in the absence of power. the DS1691 incorporates the ds1688 chip, a 32.768 khz crystal, and a lithium battery in a complete, self?contained timekeeping module. the entire unit is fully tested at dallas semiconductor such that a minimum of 10 years of timekeeping and data retention in the absence of v cc is guaranteed. for a complete description of operating conditions, electrical characteristics, bus timing, and pin descriptions other than the sqw output see the ds1689/ds1693 data sheet.
ds1688/DS1691 3 of 4 signal description sqw (square wave output) ? the sqw output signal functions identical to the ds1689/ds1693 with an exception occurring at power?up. a 32 khz square wave will be output on this pin, t rec , after a power?up condition has been detected. this condition sets the following bits enabling the 32 khz output; dv1=1, sqwe=1, and e32k=1. the square wave will be output on this pin if either sqwe=1 or e32k=1. ds1688s 28-pin soic pkg 28-pin dim min max a in. 0.697 0.728 mm 17.70 18.50 b in. 0.324 0.350 mm 8.023 8.90 c in. 0.087 0.118 mm 2.20 3.00 d in. 0.016 0.050 mm 0.40 1.27 e in. 0.002 0.014 mm 0.05 0.35 f in. 0.100 0.120 mm 2.55 3.05 g in. 0.050 mm 1.27 bsc h in. 0.453 0.500 mm 11.50 12.70 j in. 0.006 0.013 mm 0.14 0.32 k in. 0.014 0.020 mm 0.35 0.50
ds1688/DS1691 4 of 4 DS1691 28-pin 740 mil module pkg 28-pin dim min max a in. 1.520 1.540 mm 38.61 39.12 b in. 0.695 0.740 mm 17.65 18.80 c in. 0.350 0.375 mm 8.89 9.52 d in. 0.100 0.130 mm 2.54 3.30 e in. 0.015 0.030 mm 0.38 0.76 f in. 0.110 0.140 mm 2.79 3.56 g in. 0.090 0.110 mm 2.29 2.79 h in. 0.590 0.630 mm 14.99 16.00 j in. 0.008 0.012 mm 0.20 0.30 k in. 0.015 0.021 mm 0.38 0.53 note: pins 2, 3, 19 and 23 are missing by design
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