Datasheet

DS1644/DS1644P
2 of 14
PIN DESCRIPTION
PIN
PDIP PowerCap
NAME FUNCTION
1 32 A14
2 30 A12
3 25 A7
4 24 A6
5 23 A5
6 22 A4
7 21 A3
8 20 A2
9 19 A1
10 18 A0
Address Input
11 16 DQ0
12 15 DQ1
13 14 DQ2
Data Input/Output
14 17 GND Ground
15 13 DQ3
16 12 DQ4
17 11 DQ5
18 10 DQ6
19 9 DQ7
Data Input/Output
20 8 CE Active Low Chip-Enable Input
21 28 A10 Address Input
22 7 OE Active Low Output-Enable Input
23 29 A11
24 27 A9
25 26 A8
26 31 A13
Address Input
27 6
WE
Active-Low Write-Enable Input
28 5 V
CC
Power-Supply Input
- 4
RST
Active-Low Reset Output, Open Drain. Requires a pull-up resistor for
proper operation.
- 1-3,33,34 NC No Connection
- X1, X2,
V
BAT
Crystal Connection V
BAT
Battery Connection
DESCRIPTION
The DS1644 is a 32k x 8 nonvolatile static RAM with a full function real time clock, which are both
accessible in a byte-wide format. The nonvolatile timekeeping RAM is functionally equivalent to any
JEDEC standard 32k x 8 SRAM. The device can also be easily substituted for ROM, EPROM and
EEPROM, providing read/write nonvolatility and the addition of the real time clock function. The real
time clock information resides in the eight uppermost RAM locations. The RTC registers contain year,
month, date, day, hours, minutes, and seconds data in 24-hour BCD format. Corrections for the day of the
month and leap year are made automatically. The RTC clock registers are double-buffered to avoid access
of incorrect data that can occur during clock update cycles. The double-buffered system also prevents
time loss as the timekeeping countdown continues unabated by access to time register data. The DS1644
also contains its own power-fail circuitry, which deselects the device when the V
CC
supply is in an out-of-
tolerance condition. This feature prevents loss of data from unpredictable system operation brought on by
low V
CC
as errant access and update cycles are avoided.