when RTCC freezes

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Joined: Tue Mar 20, 2012 2:11 pm

when RTCC freezes

Post by diegotrex » Tue Mar 20, 2012 2:49 pm

Hi to all by a 48 years old newbie and new member,i'm Diego from Milan,Italy.
At first forgive my english.
I would like to give an active contrubution to this forum,but i have to start asking your help.
Recently i did some experiences with PIC18LF2411 and its F correspondent.
The application that i'm tryin to build should keep the real time even in case of long blackout so a backup battery or supercap for RTCC power is provided,during deep sleep only RTCC works,and after have set in deep sleep(verified,PIC consuption<1uA)the PIC waits for wake up by an EXT interrupt ,related to mains restore .
At first i used the following method to act in different ways in case RTCC was lost or not:if the current RTCC year register has different content from default value i considered the RTCC still working.
But i noticed(probably i am the last that discovered it)that when VDD goes very low but not zero,it could happen that RTCC stops counting,keeping "frozen" hours,minutes,seconds ...So at wake up checking year makes me erroneously think that RTCC never stopped.

Someone suggested me to use the DSBOR feature.Can you suggest me the right way of using it?Is it ineherent to datasheet at 4.4.1 DETECTING BOR:"A more reliable method is to simultaneously check the state of both POR and BOR"?

I tried in various way,but i'm not able to have a bit in RCON.WDTCON or in DSCONL appearing different after wake up from deep sleep or after software RESET.I did not post the code because it is likely senseless in the part related to this item.

Thanks for any hint or just for reading the above.

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