DS1285/DS1285Q
Real Time Clock
DS1285/DS1285Q
050898 1/1
FEATURES
Drop-in replacement for IBM AT computer clock/ca-
lendar
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
s to 500 ms
End of clock update cycle
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 charac-
teristics, bus timing, and pin descriptions see the
DS12885 data sheet.
PIN ASSIGNMENT
DS1285 24PIN DIP
V
CC
SQW
NC
RCLR
V
BAT
IRQ
RESET
DS
GND
R/W
AS
CS
MOT
X1
X2
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
4
3
2
1
RCLR
V
BAT
IRQ
RESET
DS
GND
R/W
28 27 26
25
24
23
22
21
20
19
DS1285Q 28-PIN PLCC
X1
MOT
NC
VCC
SQW
NC
X2
AD6
AD7
GND
CS
AS
NC
12 13 14 15 16 17 18
AD0
AD1
AD2
AD3
AD4
AD5
NC
5
6
7
8
9
10
11
NC
PIN DESCRIPTION
AD0-AD7
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
X1,X2
32.768 KHz Crystal Connections
V
BAT
+3 Volt Battery Input
RCLR
RAM Clear
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