M48T36 데이터 시트보기 (PDF) - STMicroelectronics
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M48T36 Datasheet PDF : 17 Pages
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M48T36
CLOCK OPERATIONS (cont’d)
Updating is halted when a ’1’ is written to the READ
bit, D6 in the Control Register 7FF8h. 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
Bit D7 of the Control Register 7FF8h 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 (see Table
10). Resetting the WRITE bit to a ’0’ then transfers
the values of all time registers 7FF9h-7FFFh to the
actual TIMEKEEPER counters and allows normal
operation to resume. After the WRITE bit is reset,
the next clock update will occur in one second.
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 the MSB of the seconds register. Setting it to a ’1’
stops the oscillator. The M48T36 is shipped from
SGS-THOMSON with the STOP bit set to a ’1’.
Table 10. Register Map
Address
Data
D7
D6
D5
D4
D3
D2
D1
D0
Function/Ran ge
BCD Format
7FFFh
10 Years
Year
Year
00-99
7FFEh
0
0
0 10 M.
Month
Month
01-12
7FFDh
0
0
10 Date
Date
Date
01-31
7FFCh
0
FT
0
0
0
Day
Day
01-07
7FFBh
0
0
10 Hours
Hours
Hour
00-23
7FFAh
0
10 Minutes
Minutes
Minutes
00-59
7FF9h
ST
10 Seconds
Seconds
Seconds
00-59
7FF8h
W
R
S
Calibration
Control
7FF7h
WDS BMB4 BMB3 BMB2 BMB1 BMB0 RB1 RB0
Watchdog
7FF6h
AFE
Y
ABE
Y
Y
Y
Y
Y
Interrupts
7FF5h
RPT4 Y
Al. 10 Date
Alarm Date
Alarm Date 01-31
7FF4h
RPT3 Y
Al. 10 Hours
Alarm Hours
Alarm Hours 00-23
7FF3h
RPT2
Alarm 10 Minutes
Alarm Minutes
Alarm Minutes 00-59
7FF2h
RPT1
Alarm 10 Seconds
Alarm Seconds
Alarm Seconds 00-59
7FF1h
Y
Y
Y
Y
Y
Y
Y
Y
Unused
7FF0h
WDF AF
Z
BL
Z
Z
Z
Z
Flags
Keys: S = SIGN Bit
FT = FREQUENCY TEST Bit
R = READ Bit
W = WRITE Bit
ST = STOP Bit
0 = Must be set to ’0’
Y = ’1’ or ’0’
Z = ’0’ and are Read only
AF = Alarm Flag
BL = Battery Low
10/17
WDS = Watchdog Steering Bit
BMB0–BMB4 = Watchdog Multiplier Bits
RB0–RB1 = Watchdog Resolution Bits
AFE = Alarm Flag Enable
ABE = Alarm in Battery Back-up Mode Enable
RPT1–RPT4 = Alarm Repeat Mode Bits
WDF = Watchdog Flag
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