DESCRIPTION
The DS12C887A real-time clock plus RAM is designed to be a direct upgrade replacement for the DS12887A in existing IBM-compatible personal computers to add hardware year-2000 compliance. A century byte was added to memory location 50, 32h, as called out by the PC AT specification.

FEATURES
● Drop-in replacement for IBM AT computer clock/calendar
● Pin compatible with the MC146818B and DS1287A
● 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, days, day of the week, date, month, and year with leap year compensation valid up to 2100
● 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 128 RAM locations
      – 15 bytes of clock and control registers
      – 113 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 500ms
      – En-of-clock update cycle
● Century register