m48t128y STMicroelectronics, m48t128y Datasheet - Page 11

• Manufacturer Part Number: m48t128y
• Description: 5.0 Or 3.3v, 1 Mbit 128 Kb X 8 Timekeeper Sram
• Manufacturer: STMicroelectronics

CLOCK OPERATIONS
Reading the Clock
Updates to the TIMEKEEPER
be halted before clock data is read to prevent
reading data in transition. The BiPORT™ TIME-
KEEPER cells in the RAM array are only data reg-
isters and not the actual clock counters, so
updating the registers can be halted without dis-
turbing the clock itself.
Updating is halted when a '1' is written to the
READ Bit, D6 in the Control Register (1FFF8h). As
long as a '1' remains in that position, updating is
halted. After a halt is issued, the registers reflect
the count; that is, the day, date, and time that were
current at the moment the halt command was is-
sued. All of the TIMEKEEPER registers are updat-
ed simultaneously. A halt will not interrupt an
update in progress. Updating is within a second af-
ter the bit is reset to a '0.'
Setting the Clock
Bit D7 of the Control Register (1FFF8h) is the
WRITE Bit. Setting the WRITE Bit to a '1,' like the
Table 5. Register Map
Keys: S = SIGN Bit
Address
1FFFDh
1FFFCh
1FFFFh
1FFFEh
1FFFBh
1FFFAh
1FFF9h
1FFF8h
R = READ Bit
W = WRITE Bit
ST = STOP Bit
0 = Must be set to '0'
Z = '0' and are Read only
Y = '1' or '0'
D7
ST
W
0
0
0
0
0
D6
FT
R
0
0
0
10 Years
10 Seconds
10 Minutes
D5
S
0
0
10 Hours
10 Date
®
registers should
10 M
D4
0
Data
D3
0
Calibration
D2
Seconds
READ Bit, halts updates to the TIMEKEEPER reg-
isters. The user can then load them with the cor-
rect day, date, and time data in 24 hour BCD
format (see
WRITE Bit to a '0' then transfers the values of all
time registers 1FFFFh-1FFF9h to the actual TIME-
KEEPER counters and allows normal operation to
resume. After the WRITE Bit is reset, the next
clock update will occur one second later.
Stopping and Starting the Oscillator
The oscillator may be stopped at any time. If the
device is going to spend a significant amount of
time on the shelf, the oscillator can be turned off to
minimize current drain on the battery. The STOP
Bit is located at Bit D7 within 1FFF9h. Setting it to
a '1' stops the oscillator. The M48T128Y/V is
shipped from STMicroelectronics with the STOP
Bit set to a '1.' When reset to a '0,' the M48T128Y/
V oscillator starts after one second.
Minutes
Month
Hours
Date
Year
Day
D1
Table 5., page
D0
M48T128Y, M48T128V*
Seconds
Minutes
Control
Month
Hours
Date
Year
Day
Function/Range
BCD Format
11). Resetting the
00-99
01-12
01-31
01-07
00-23
00-59
00-59
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