M48T08-100PC1TR View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
M48T08-100PC1TR Datasheet PDF : 27 Pages
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M48T08, M48T08Y, M48T18
CLOCK OPERATIONS
Reading the Clock
Updates to the TIMEKEEPER® registers should
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, the seventh bit in the control register.
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 the time that
were current at the moment the halt command was
issued.
All of the TIMEKEEPER registers are updated si-
multaneously. A halt will not interrupt an update in
progress. Updating is within a second after the bit
is reset to a '0.'
Setting the Clock
The eighth bit of the control register is the WRITE
Bit. Setting the WRITE Bit to a '1,' like the READ
Bit, halts updates to the TIMEKEEPER registers.
The user can then load them with the correct day,
date, and time data in 24 hour BCD format (on Ta-
ble 5.). Resetting the WRITE Bit to a '0' then trans-
fers the values of all time registers (1FF9h-1FFFh)
to the actual TIMEKEEPER counters and allows
normal operation to resume. The FT Bit and the
bits marked as '0' in Table 5. must be written to '0'
to allow for normal TIMEKEEPER and RAM oper-
ation.
See the Application Note AN923, “TIMEKEEPER®
Rolling Into the 21st Century” for information on
Century Rollover.
Table 5. Register Map
Data
Address
D7
D6
D5
D4
D3
D2
D1
D0
1FFFh
10 Years
Year
1FFEh
0
0
0
10 M
Month
1FFDh
0
0
10 Date
Date
1FFCh
0
FT
0
0
0
Day
1FFBh
0
0
10 Hours
Hours
1FFAh
0
10 Minutes
Minutes
1FF9h
ST
10 Seconds
Seconds
1FF8h
W
R
S
Calibration
Keys: S = SIGN Bit
FT = FREQUENCY TEST Bit (Set to '0' for normal clock operation)
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
13/27
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