DESCRIPTION
The DS1285 Real Time Chip is a direct replacement for the MC146818A in IBM AT computer clock/calendar and other applications. For a complete description of operating conditions, electrical and mechanical charac
teristics, bus timing, and pin descriptions see the DS12885 data sheet.

FEATURES
• Drop-in replacement for IBM AT computer clock/calendar
• Pin configuration closely matches MC146818A
• Counts seconds, minutes, hours, day of the week,date, month, and year with leap year compensation
• 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 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 µs to 500 ms
– End of clock update cycle
• Optional 28-pin PLCC surface mount package