DS1642 Datasheet, PDF (2/13 Pages) Dallas Semiconductor – Nonvolatile Timekeeping RAM

PIN DESCRIPTION
PIN NAME
FUNCTION
1
A7
2
A6
3
A5
4
A4
5
A3
6
A2 Address Input
7
A1
8
A0
19
A10
22
A9
23
A8
9
DQ0
10
DQ1
11
DQ2
13
14
DQ3
DQ4
Data Input/Output
15
DQ5
16
DQ6
17
DQ7
12
GND Ground
18
CE Active-Low Chip-Enable Input
20
OE Active-Low Output-Enable Input
21
WE Active-Low Write-Enable Input
24
V_CC Power-Supply Input
DS1642
DESCRIPTION
The DS1642 is a 2k x 8 nonvolatile static RAM and a full-function real-time clock (RTC), both of which
are accessible in a bytewide format. The nonvolatile time keeping RAM is pin and function equivalent to
any JEDEC-standard 2k x 8 SRAM. The device can also be easily substituted in ROM, EPROM, and
EEPROM sockets, 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
DS1642 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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