DS1287 real time clock DS1287 050898 1/1 features ? drop-in replacement for ibm at computer clock/ca- lendar ? pin compatible with the mc146818a ? 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, day of the week, date, month, and year with leap year compensation ? binary or bcd representation of time, calendar, and alarm ? 12- 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 64 ram locations 14 bytes of clock and control registers 50 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 122 m s to 500 ms end of clock update cycle pin assignment 24 pin encapsulated package v cc sqw nc nc nc irq reset ds nc r/w as cs mot nc nc ad0 ad1 ad2 ad3 ad4 ad5 ad6 ad7 gnd 1 2 3 4 5 6 7 8 9 10 11 12 24 23 22 21 20 19 18 17 16 15 14 13 pin description ad0ad7 - multiplexed address/data bus nc - 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 (open drain) sqw - square wave output v cc - +5 volt supply gnd - ground description the DS1287 real time clock is designed to be a direct replacement for the mc146818a. for a complete description of operating conditions, electrical and mechanical characteristics, bus timing, and pin descrip- tions see the ds12887 data sheet.
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