DS12887
Real Time Clock
www.dalsemi.com
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
PIN ASSIGNMENT
NC
PIN DESCRIPTION
AD0–AD7
NC
MOT
CS
§
§
§
AS
R/
W
DS
RESET
IRQ
SQW
V
CC
GND
– Multiplexed Address/Data Bus
– No Connection
– Bus Type Selection
– Chip Select
– Address Strobe
– Read/Write Input
– Data Strobe
– Reset Input
– Interrupt Request Output
– Square Wave Output
– +5 Volt Supply
– Ground
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. The functions include a nonvolatile
time–of–day clock, an alarm, a one-hundred–year calendar, programmable interrupt, square wave
1 of 19
110899
DALLAS [ DALLAS SEMICONDUCTOR ]
