CHAPTER 7-3: VBAT Domain(B)
332 FM4 Peripheral Manual, Doc. No. 002-04856 Rev. *E
Not Linking with Clock Control Circuit but Waiting for Oscillation Stabilization
It is necessary to not link the 32 kHz oscillation circuit with the clock control circuit when always using the
backup power supply to keep the RTC operating. Nonetheless, the 32 kHz oscillation circuit and RTC in
the VBAT Domain do not have the oscillation stabilization wait function.
When the 32 kHz clock is used only for the RTC, a software timer can be used to count the oscillation
stabilization wait time. However, if the 32 kHz clock is also used in subrun mode, the clock oscillation
stabilization wait function becomes necessary.
In the above situation, follow the procedure below to enable the oscillation stabilization wait function only
at the start of oscillation.
Example of setting procedure
Enable the cooperative operation with the clock control circuit and start the oscillation.
After the oscillation stabilization wait time has elapsed, disable the cooperative operation with the clock
control circuit.
(1) Set the Register of VBAT I/O Port to use the 32 kHz oscillation circuit.
(2) Set an appropriate current value for the current that is to flow to the oscillation amplifier circuit.
(3) Set the oscillation boost time.
(4) Enable the cooperative operation with the clock control circuit. In addition, enable the oscillation.
(5) Wait for the stabilization of the 32 kHz oscillation.
(6) Disable the cooperative operation with the clock control circuit. (The oscillation keeps being enabled.)
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