VSBC-6862
Rev 1.43
52
48T37V partial register map is:
Base +
D7
D6
D5
D4
D3
D2
D1
D0
Function (Range) BCD format
$7FFF
10 Years
Year
Year (00-99)
$7FFE
0 0 0
10M.
Month
Month
(01-12)
$7FFD
0
0
10 Date
Date
Date (01-31)
$7FFC
0 FT 0 0 0
Day
Century/Day
(0-1/01-07)
$7FFB
0
0
10 Hours
Hours
Hour (00-23)
$7FFA
0
10 Minutes
Minutes
Minutes (00-59)
$7FF9
ST
10 Seconds
Seconds
Seconds (00-59)
$7FF8 W R S
Calibration
Control
$7FF7 WDS BMB4 BMB3 BMB2 BMB1 BMB0 RB1 RB0
Watchdog
$7FF6
AFE
0
ABE
0 0 0 0 0
Interrupts
$7FF5
RPT4
0
Alarm 10 Date
Alarm Date
Alarm Date (01-31)
$7FF4
RPT3
0
Alarm 10 Hours
Alarm Hours
Alarm Hours (00-23)
$7FF3
RPT2
Alarm 10 Minutes
Alarm Minutes
Alarm Minutes (00-59)
$7FF2
RPT1
Alarm 10 Second
Alarm Seconds
Alarm Seconds (00-59)
$7FF1
1000 Years
100 Years
Century
$7FF0 WDF AF
Z
BL
Z
Z
Z
Z
Flags
With:
S = sign bit
AF = Alarm Flag
FT = Frequency Test bit
BL = Battery Low Flag
R = Read Bit
WDS = Watchdog Steering Bit
W = Write Bit
BMB0-BMB4 = Watchdog Multiplier Bits
ST = Stop Bit
RB0-RB1 = Watchdog Resolution Bits
0 = Must be set to ’0’
AFE = Alarm Flag Enable
Z = ’0’ and are Read only
ABE = Alarm in Battery Back-up Mode Enable
WDS = Watchdog Steering Bit
RPT1-RPT4 = Alarm Repeat Mode Bits
WDF = Watchdog Flag
4.5.1. RTC registers read operation
The RTC registers are continuously updated by the device.
Updates to the RTC registers should be halted before clock data is read to prevent reading data in
transition.
Because the registers are only copy of the clock counters, 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 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 was current at the moment the halt
command was issued. All of the RTC registers are updated simultaneously. A halt will not interrupt an
update in progress. Updating is within a second after the bit is reset to a ’0’.
4.5.2. RTC registers write operation
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 RTC registers. The user can then load them with the correct day, date, and
time data in 24 hour BCD format. Resetting the WRITE bit to a ’0’ then transfers the values of all time
registers 7FF9h-7FFFh to the actual RTC counters and allows normal operation to resume. After the
WRITE bit is reset, the next clock update will occur in approximately one second.
See the ST Microelectronics Application Note AN923 "TIMEKEEPER rolling into
the 21st century" on the ST Web site for information on Century Rollover.
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