DESCRIPTION

The DS12C887 Real Time Clock plus RAM is designed as a direct upgrade replacement for the DS12887 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. A lithium energy source, quartz crystal, and write-protection circuitry are contained within a 24–pin dual in-line package.

FEATURES

■ Drop-in replacement for IBM AT computer

clock/calendar

■ Pin compatible with the MC146818B and

DS1287

■ 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 ms to 500 ms

– End of clock update cycle

■ Century register