M48T512V-70PM1 查看數據表（PDF） - STMicroelectronics
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M48T512V-70PM1 Datasheet PDF : 21 Pages
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M48T512Y, M48T512V*
CLOCK OPERATIONS
Reading the Clock
Updates to the TIMEKEEPER® registers should
be halted before clock data is read to prevent
reading data in transition (see Table 5.). The Bi-
PORT™ TIMEKEEPER cells in the RAM array are
only data registers and not the actual clock
counters, so updating the registers can be halted
without disturbing the clock itself.
Updating is halted when a '1' is written to the
READ Bit, D6 in the Control Register (7FFF8h). 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 occurs 1 second af-
ter the READ Bit is reset to a '0.'
Setting the Clock
Bit D7 of the Control Register (7FFF8h) is the
WRITE Bit. Setting the WRITE Bit to a '1,' like the
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 Table 5., page 11). Resetting the
WRITE Bit to a '0' then transfers the values of all
time registers 7FFFFh-7FFF9h to the actual TIME-
KEEPER counters and allows normal operation to
resume. After the WRITE Bit is reset, the next
clock update will occur approximately one second
later. See Application Note, AN923, “TIMEKEEP-
ER® Rolling Into the 21st Century” on the ST Web
Site for more information on Century Rollover.
Note: Upon power-up, both the WRITE Bit and the
READ Bit will be reset to '0.'
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 7FFF9h. Setting it to
a '1' stops the oscillator. The M48T512Y/V is
shipped from STMicroelectronics with the STOP
bit set to a '1.' When reset to a '0,' the M48T512Y/
V oscillator starts after approximately one second.
Note: It is not necessary to set the WRITE Bit
when setting or resetting the FREQUENCY TEST
Bit (FT) or the STOP Bit (ST).
Table 5. Register Map
Data
Address
D7
D6
D5
D4
D3
D2
D1
D0
7FFFFh
10 Years
Year
7FFFEh
0
0
0
10 M
Month
7FFFDh
0
0
10 Date
Date
7FFFCh
0
0
0
0
0
Day
7FFFBh
0
0
10 Hours
Hours
7FFFAh
0
10 Minutes
Minutes
7FFF9h ST
10 Seconds
Seconds
7FFF8h W
R
S
Calibration
Keys: S = SIGN Bit
R = READ Bit
W = WRITE Bit
ST = STOP Bit
0 = Must be set to '0'
Function/Range
BCD Format
Year
Month
Date
Day
Hours
Minutes
Seconds
Control
00-99
01-12
01-31
01-07
00-23
00-59
00-59
11/21
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