DS12C887
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
– 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
PIN ASSIGNMENT
MOT
NC
NC
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7
GND
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
V
CC
SQW
NC
NC
NC
IRQ
RESET
DS
NC
R/W
AS
CS
DS12C887 24-Pin
ENCAPSULATED PACKAGE
PIN DESCRIPTION
AD0-AD7 - Multiplexed Address/Data Bus
NC
- No Connect
MOT
- Bus Type Selection
CS
- RTC Chip Select Input
AS
- Address Strobe
R/
W
- Read/Write Input
DS
- Data Strobe
RESET
- Reset Input
IRQ
- Interrupt Request Output
SQW
- Square Wave Output
V
CC
- +5 Volt Main Supply
GND
- Ground
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.
As such, the DS12C887 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 generator, and 113 bytes of nonvolatile static RAM. The real time clock is
distinctive in that time-of-day and memory are maintained even in the absence of power.
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020900
DALLAS [ DALLAS SEMICONDUCTOR ]
