DS1285/DS1285Q DS1285/DS1285Q Real Time Clock FEATURES PIN ASSIGNMENT • Drop-in replacement for IBM AT computer clock/ca- MOT 1 24 VCC X1 2 23 SQW X2 3 22 NC AD0 4 21 RCLR seconds, minutes, hours, day of the week, date, month, and year with leap year compensation AD1 5 20 VBAT AD2 6 19 IRQ • Binary or BCD representation of time, calendar, and AD3 7 18 RESET AD4 8 17 DS AD5 9 16 GND • 12- or 24-hour clock with AM and PM in 12-hour mode AD6 10 15 R/W AD7 11 14 AS • Daylight Savings Time option GND 12 13 CS lendar • Pin configuration closely matches MC146818A • Counts alarm • Selectable between Motorola and Intel bus timing • Optional 28-pin PLCC surface mount package 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 characteristics, bus timing, and pin descriptions see the DS12885 data sheet. NC VCC SQW MOT X1 24 VBAT AD2 7 23 IRQ AD3 8 22 RESET AD4 9 21 DS AD5 10 20 GND 19 11 12 13 14 15 16 17 18 R/W NC RCLR NC 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 6 CS AS • Three 1 28 27 26 25 GND • Bus compatible interrupt signals (IRQ) 3 2 5 AD1 AD7 • Programmable square wave output signal 4 AD0 NC – 14 bytes of clock and control registers – 50 bytes of general purpose RAM AD6 • Interfaced with software as 64 RAM locations X2 • Multiplex bus for pin efficiency NC DS1285 24–PIN DIP DS1285Q 28-PIN PLCC PIN DESCRIPTION AD0-AD7 NC MOT CS AS R/W DS RESET IRQ SQW VCC GND X1,X2 VBAT 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 drain) Square Wave Output +5 Volt Supply Ground 32.768 KHz Crystal Connections +3 Volt Battery Input RAM Clear 050898 1/1