Document
DS1287A
DS1287A Real Time Clock
FEATURES
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PIN ASSIGNMENT
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 VCC SQW NC RCLR NC IRQ RESET DS NC R/W AS CS
• Drop-in replacement for IBM AT computer clock/calendar
• Pin compatible with the MC146818A • Totally nonvolatile with over 10 years of operation in
the absence of power
• Self-contained • Counts
subsystem includes lithium, quartz, and support circuitry seconds, minutes, hours, day of the week, date, month, and year with leap year compensation alarm
• Binary or BCD representation of time, calendar, and • 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
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
• 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 ms to 500 ms – End of clock update cycle
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 characteristics, bus timing, and pin descriptions see the DS12887A data sheet.
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