RA6: how to detect VBAT drop-outs?

Question

How can I detect a temporary VBAT power loss during VCC power off? 
 Background: I need to detect e.g. a previous battery change after the device is powered again (coming out of reset).

dsherman26 · Accepted Answer

If you are using the RTC, you can easily detect if has stopped when powered up by looking at the START bit in the RCR2 register. If VBATT hasn't been lost and the RTC is supposed to be running, then START will still be set. If it stopped, then START will be clear.

JimB · Answer

In my experience this is done with energy reserve (e.g. capacitor) added to MCU, and resistor divider network connected to ADC pin where VBAT can be monitored. Upon detection of low VBAT, need the energy reserve to last long enough for the MCU to do its housekeeping that might be required and gracefully shut down.

RA6: how to detect VBAT drop-outs?

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