The BPF flag is set on backup power failure (either capacitor or battery). The backup power fail flag (BPF) is issued on the next power-up in case of backup power failure. The BPF flag is set in the event of backup voltage falling lower than VBAKFAIL. Once you have cleared it will remain 0 until the device experience another backup power failure (with backup power applied). With no backup power since it is a volatile bit it will not set. This is expected behavior.
Thank you for your response.
Our SW design, allows soft resets to happen in order to enter different modes of operation. Is it possible to NOT clear the BPF flag and still use the RTC normally?
I am asking this question because the datasheet states, "User must reset this bit to clear this flag.". If I do not clear the flag, what are the affects?
Thank you for your time.
Please find my comments below.
Q) Our SW design, allows soft resets to happen in order to enter different modes of operation. Is it possible to NOT clear the BPF flag and still use the RTC normally?
Ans) Yes, you can use RTC normally. The primary purpose of the BPF is to indicate to the user that there was a backup power failure. Now it is upto the user to use this information as he/she deems fit.
The only disadvantage of not clearing this flag is you will not be able to detect future failures of backup power. It can happen over time say your backup cap or battery has worn out and not performing as expected, so you will fail to catch this.