DESCRIPTION
The DS12887 Real Time Clock plus RAM is designed to be a direct replacement for the DS1287. The DS12887 is identical in form, fit, and function to the DS1287, and has an additional 64 bytes of general purpose RAM. Access to this additional RAM space is determined by the logic level presented on AD6 during the address portion of an access cycle. A lithium energy source, quartz crystal, and write– protection circuitry are contained within a 24–pin dual in-line package. As such, the DS12887 is a complete subsystem replacing 16 components in a typical application.

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
   – 14 bytes of clock and control registers
   – 114 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