M41T81S – How to handle RTC Oscillator Stop/Fail Bits

[Central SUPPORT]

In Datasheet Table 5 it says that the Oscillator Fail bit OF (Clock register: bit 2 of address 0Fh) starts at “1�? after initial power-up. So, in this case (or whenever when I find OF bit at “1�?) I will have to restart the oscillator by pulsing Oscillator Stop bit ST (Clock register: bit 7 of address 01h) resp, write “1�?, then “0�?.

Then it says that I have to wait another 4 seconds before clearing OF bit. Is this a must?

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[Central SUPPORT · Accepted solution]

Technically, you can clear the OF bit without waiting 4 sec, but it can happen that system will set it again if the oscillator is not stable yet.

Refer to AN3060 “Applications guide for serial real-time clocks (RTCs)�?, chapter 6.1 for more details.