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MSP430FR5969 RTC_B and battery backup...

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Bit new to the MSP430 - I have the new FR5969 launchpad and was playing with RTC_B.


Ideally, I'd like to protect the RTC over a main power failure, i.e. keep it ticking but stop the rest of the processor (think clock that doesn't lose track during a power outage).


Is there a way to do this without an external RTC (e.g. DS3231 etc.)? Some other MSP430s have a "VBAT" pin that helps in this, but not the FR5969...





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You could think in software solutions.


Say you have a little circuit (two diodes) to have either an external power (from the mains) or a secondary supply (battery) on your supply pins. Then have a single input pin connected to only the external power.

Whenever your circuit is running off of battery supply, the input pin will have a low voltage. You can then shut down all foreground tasks and go into low power mode (LPM3). You let RTC_B serve an interrupt for software timekeeping (counting hours/days/etc).

Then whenever the external power comes back up again, you could have an interrupt trigger and start your foreground tasks again.

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