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Real-Time Clock: Clock Operation
10006757-02 PmPPC7448 User’s Manual
9-3
ST: Stop bit
1=Stops the oscillator
0=Restarts the oscillator within one second
CEB: Century Enable Bit
1=Causes CB to toggle either from 0 to 1 or from 1 to 0 at the turn of the century
0=CB will not toggle
CB: Century Bit
Day: Day of the week
Date: Day of the month
OUT: Output level
1=Default at initial power-up
0=FT/OUT (pin 7) driven low when FT is also zero
FT: Frequency Test bit
1=When oscillator is running at 32,768 Hz, the FT/OUT pin will toggle at 512 Hz
0=The FT/OUT pin is an output driver (default at initial power-up)
S: Sign bit
1=Positive calibration
0=Negative calibration
Calibration: Calibration bits The calibration circuit adds or subtracts counts from the oscillator divider
circuit at the divide by 256 stage. The number of times pulses are blanked (subtracted, neg-
ative calibration) or split (added, positive calibration) depends on this five-bit byte. Adding
counts accelerates the clock, and subtracting counts slows the clock down.
X: Don’t care bit