M48T129 ST Microelectronics, M48T129 Datasheet - Page 3

• Manufacturer Part Number: M48T129
• Description: 3.3V-5V 1 Mbit 128Kb x8 TIMEKEEPER SRAM
• Manufacturer: ST Microelectronics

Figure 3. Block Diagram
cess. Insertion of the SNAPHAT housing after
reflow prevents potential battery damage due to
the high temperatures required for device surface-
mounting. The SNAPHAT housing is keyed to pre-
vent reverse insertion.
The SNAPHAT battery package is shipped sepa-
rately in plastic anti-static tubes or in Tape & Reel
form. The part number is ”M4Txx-BR12SH1”.
The 32 pin 600 mil DIP Hybrid houses a controller
chip, SRAM, quartz crystal, and a long life lithium
button cell in a single package.
Figure 3 illustrates the static memory array and the
quartz controlled clock oscillator. The clock loca-
tions contain the century, year, month, date, day,
hour, minute, and second in 24 hour BCD format.
Corrections for 28, 29 (leap year), 30, and 31 day
months are made automatically. The nine clock
bytes (1FFFFh-1FFF9h and 1FFF1h) are not the
actual clock counters, they are memory locations
consisting of BiPORT
within the static RAM array.
The M48T129Y/V includes a clock control circuit
which updates the clock bytes with current infor-
mation once per second. The information can be
accessed by the user in the same manner as any
other location in the static memory array. Byte
32,768 Hz
CRYSTAL
LITHIUM
CELL
read/write memory cells
OSCILLATOR AND
VOLTAGE SENSE
CLOCK CHAIN
SWITCHING
CIRCUITRY
AND
V CC
POWER
V PFD
1FFF8h is the clock control register. This byte con-
trols user access to the clock information and also
stores the clock calibration setting.
Byte 1FFF7h contains the watchdog timer setting.
The watchdog timer can generate either a reset or
an interrupt, depending on the state of the Watch-
dog Steering bit (WDS). Bytes 1FFF6h-1FFF2h in-
clude bits that, when programmed, provide for
clock alarm functionality. Alarms are activated
when the register content matches the month,
date, hours, minutes, and seconds of the clock
registers. Byte 1FFF1h contains century informa-
tion. Byte 1FFF0h contains additional flag informa-
tion pertaining to the watchdog timer, the alarm
condition and the battery status. The M48T129Y/V
also has its own Power-Fail Detect circuit. This
control circuitry constantly monitors the supply
voltage for an out of tolerance condition. When
V
the TIMEKEEPER register data and external
SRAM, providing data security in the midst of un-
predictable system operation. As V
control circuitry automatically switches to the bat-
tery, maintaining data and clock operation until
valid power is restored.
CC
is out of tolerance, the circuit write protects
SRAM ARRAY
TIMEKEEPER
131,056 x 8
REGISTERS
16 x 8
V SS
M48T129Y, M48T129V
RST
IRQ/FT
A0-A16
DQ0-DQ7
E
W
G
CC
AI02583
falls, the
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