DS1287A
Real Time Clock
DS1287A
022798 1/1
FEATURES
Drop-in replacement for IBM AT computer clock/ca-
lendar
Pin compatible with the MC146818A
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, 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
m
s to 500 ms
End of clock update cycle
PIN ASSIGNMENT
24 PIN ENCAPSULATED PACKAGE
V
CC
SQW
NC
RCLR
NC
IRQ
RESET
DS
NC
R/W
AS
CS
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
PIN DESCRIPTION
AD0AD7
-
Multiplexed address/data bus
NC
-
No connection
MOT
-
Bus type selection
CS
-
Chip select
AS
-
Address strobe
R/W
-
Read/write input
DS
-
Data strobe
RESET
-
Reset input
IRQ
-
Interrupt request output (open
drain)
SQW
-
Square wave output
V
CC
-
+5 volt supply
GND
-
Ground
RCLR
-
RAM clear
DESCRIPTION
The DS1287A is identical to the DS1287 with the addi-
tion of the RAM clear pin. For a complete description of
operating conditions, electrical and mechanical charac-
teristics, bus timing, and pin descriptions see the
DS12887A data sheet.
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