
1 of 38
050802
FEATURES
Incorporates industry standard DS1287 PC clock
plus enhanced features:
Y2K compliant
+3V or +5V operation
SMI recovery stack
64-bit silicon serial number
Power-control circuitry supports system
power-on from date/time alarm or key
closure
32kHz output on power-up
Crystal select bit allows RTC to operate with
6pF or 12.5pF crystal
114 bytes user NV RAM
Auxiliary battery input
4kB additional NV RAM
RAM clear input
Century register
Date alarm register
Compatible with existing BIOS for original
DS1287 functions
Available as chip (DS17485) or standalone
module with embedded battery and crystal
(DS17487)
Timekeeping algorithm includes leap-year
compensation valid up to 2100
Underwriters Laboratory (UL) recognized
TYPICAL OPERATING CIRCUIT
PIN ASSIGNMENT
PWR
NC
1
2
3
4
5
6
7
8
9
10
11
12
23
22
21
20
19
18
17
16
15
14
13
DS17487 24-Pin
Encapsulated Package
NC
AD0
AD1
AD2
AD3
AD4
AD5
AD6
AD7
GND
V
CC
SQW
V
BAUX
RCLR
NC
IRQ
KS
RD
NC
WR
ALE
CS
24
PWR
X1
1
2
3
4
5
6
7
8
9
10
11
12
23
22
21
20
19
18
17
16
15
14
13
DS17485 24-Pin DIP
DS17485S 24-Pin SO
X2
AD1
AD2
AD3
AD4
AD5
AD6
AD7
GND
V
CC
SQW
V
BAUX
RCLR
V
BAT
IRQ
KS
RD
GND
WR
ALE
CS
24
AD0
V
BAT
RCLR
V
BAUX
SQW
V
CC
V
PWR
X1
X2
NC
ADO
AD1
AD2
IRQ
1
2
3
4
5
6
7
8
9
28
27
26
25
24
23
22
21
20
19
18
17
16
15
KS
RD
GND
WR
ALE
CS
GND
GND
AD7
AD6
NC
AD5
AD4
AD3
10
11
12
13
14
DS17485E 28-Pin TSOP
DS17485/DS17487
3V/5V Real-Time Clock
www.maxim-ic.com