DS1644P Datasheet, PDF (2/13 Pages) Dallas Semiconductor – Nonvolatile Timekeeping RAM

DS1644/DS1644P
PIN DESCRIPTION
PIN
PDIP PowerCap
NAME
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
11
16
DQ0
12
15
DQ1
13
14
DQ2
14
17
GND
15
13
DQ3
16
12
DQ4
17
11
DQ5
18
10
DQ6
19
9
DQ7
20
8
CE
21
28
A10
22
7
OE
23
29
A11
24
27
A9
25
26
A8
26
31
A13
27
6
WE
28
5
V_CC
-
4
RST
-
1-3,33,34
NC
-
X1, X2,
V_BAT
Address Input
FUNCTION
Data Input/Output
Ground
Data Input/Output
Active Low Chip-Enable Input
Address Input
Active Low Output-Enable Input
Address Input
Active-Low Write-Enable Input
Power-Supply Input
Active-Low Reset Output, Open Drain. Requires a pullup resistor for
proper operation.
No Connection
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.
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