m48t129v STMicroelectronics, m48t129v Datasheet - Page 7

• Manufacturer Part Number: m48t129v
• Description: 5.0 Or 3.3v, 1 Mbit 128 Kbit X 8 Timekeeper Sram
• Manufacturer: STMicroelectronics

OPERATING MODES
Figure 4., page 5
ray and the quartz controlled clock oscillator. The
clock locations contain the century, year, month,
date, day, hour, minute, and second in 24 hour
BCD format. Corrections for 28, 29 (leap year -
valid until 2100), 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™ READ/WRITE memory cells 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
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
Table 2. Operating Modes
Note: X = V
Deselect
WRITE
READ
READ
Deselect
Deselect
Mode
1. See
IH
Table 12., page 23
or V
IL
; V
V
SO
illustrates the static memory ar-
SO
= Battery Back-up Switchover Voltage.
4.5 to 5.5V
3.0 to 3.6V
to V
V
V
PFD
or
for details.
SO
CC
(1)
(min)
(1)
V
V
V
V
E
X
X
IH
IL
IL
IL
V
V
G
X
X
X
X
an interrupt, depending on the state of the Watch-
dog Steering Bit (WDS). Bytes 1FFF6h-1FFF2h
include 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
SRAM, providing data security in the midst of un-
predictable system operation. As V
Battery Back-up Switchover Voltage (V
control circuitry automatically switches to the bat-
tery, maintaining data and clock operation until
valid power is restored.
IH
IL
CC
is out of tolerance, the circuit write protects
V
V
V
W
X
X
X
IH
IH
IL
DQ0-DQ7
High Z
High Z
High Z
High Z
D
®
D
OUT
IN
register data and external
M48T129Y, M48T129V
Battery Back-up Mode
CMOS Standby
Standby
CC
Power
Active
Active
Active
falls below
SO
), the
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