DS1287A DS1287A Real Time Clock FEATURES PIN ASSIGNMENT • Drop-in replacement for IBM AT computer clock/calendar MOT 1 24 VCC NC 2 23 SQW NC 3 22 NC AD0 4 21 RCLR AD1 5 20 NC • Self-contained AD2 6 19 IRQ AD3 7 18 RESET • Counts AD4 8 17 DS seconds, minutes, hours, day of the week, date, month, and year with leap year compensation AD5 9 16 NC AD6 10 15 R/W • Binary or BCD representation of time, calendar, and AD7 11 14 AS GND 12 13 CS • Pin compatible with the MC146818A • Totally nonvolatile with over 10 years of operation in the absence of power subsystem includes lithium, quartz, and support circuitry 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 s to 500 ms – End of clock update cycle 24 PIN ENCAPSULATED PACKAGE PIN DESCRIPTION AD0–AD7 NC MOT CS AS R/W DS RESET IRQ drain) SQW VCC GND RCLR - Multiplexed address/data bus No connection Bus type selection Chip select Address strobe Read/write input Data strobe Reset input Interrupt request output (open - Square wave output +5 volt supply Ground RAM clear DESCRIPTION The DS1287A is identical to the DS1287 with the addition of the RAM clear pin. For a complete description of operating conditions, electrical and mechanical charac- teristics, bus timing, and pin descriptions see the DS12887A data sheet. 022798 1/1