CHAPTER 7-3: VBAT Domain(B)
316 FM4 Peripheral Manual, Doc. No. 002-04856 Rev. *E
2.4 Power-on Circuit
The FM4 Family has a power-on circuit independent of the VCC power supply pin detecting the power-on
of the VBAT Domain.
Overview of Function of Power-on Circuit
The power-on circuit in the VBAT Domain has the following function.
VBAT power supply pin rising edge detection function
While the power-on circuit is outputting the power-on signal, Power-on bit (PON) in the VDET Register
reads 1.
The power-on signal keeps being asserted until 0 is written to Power-on bit (PON) in the VDET Register.
The power-on signal and the value of Power-on bit (PON) in the VDET Register are not affected by
turning on and off of the VCC power supply.
If the power-on circuit in the VBAT Domain is initialized according to the following flow, while a peripheral
function is initialized at a VCC rising edge, the initialization of the VBAT Domain that is in operation is
skipped and the RTC continues running.
Figure 2-6 Flow of Power-on Judgment and Initialization of VBAT Power Domain
Notes:
− The power-on circuit in the VBAT Domain does not have the VBAT power supply pin low voltage
detection function. (The FM4 Family does not have the VBAT power supply pin low voltage
detection function.)
− While the power-on signal is being asserted, the values of the registers of the VBAT Domain
(RTC, 32 kHz oscillation circuit, VBAT I/O port control circuit, backup registers) are fixed at their
respective initial values. Before setting these circuits, write 0 to Power-on bit (PON) in the VDET
Register to clear the power-on signal.
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