Hi Peter,

This variable that you are talking about - will this be stored in
EEPROM/flash or RAM? I think that RAM contents may be destroyed during
a brown-out condition. Probably not, but I wouldn't rely on it.

It seems to me that others have already mentioned that there are
status bits in the PIC which will tell you whether the last reset was
a power-on reset or a brown-out condition. Why not simply check for
this at every boot and if it was a brown-out reset, then do not
operate. Replacing the batteries will cause a power-on reset instead
and then you can resume normal operation.

Sean


On Mon, Oct 10, 2011 at 9:26 AM, IB Peter Feucht <feuchts@kabelbw.de> wrote=
:
> Hi,
>
> thanks anybody for the hints, very helpful!
>
> 1. I read paragraph 12.3.5. but when 12.3.6. started with power-up stuff =
I
> stopped read=EDng, power UP was not my problem. I learned: Better read so=
me
> pages more.
>
> 2. Some guys were discussing, if BOR is useful for battery detection. Yes=
,
> you are right, if the circuitry is always operated in "full power mode". =
In
> this case it will never leave the brown out condition. But in my device t=
he
> user starts the software by a key press, then it's operating for 15 or 20
> minutes, consuming much power, but after that it goes to sleep mode,
> consuming nearly zero amps. During this sleep the batteries may recover a=
nd
> next time my PIC sees a "full" battery, but during operation the voltage =
can
> go low again.
> That's why I was looking for this distinction.
>
> What I intend to do:
>
> I have a variable which is reset by every cold boot (initialized to zero
> when PIC starts).
> When user presses the key, this variable is set to 1 (I assume that a BOR
> will happen)
> After normal operation (when no BOR happened) I reset this variable again
> and the PIC goes to sleep.
> So when it wakes up again, it sees a reset variable. Fine.
> But when a BOR occured during operation, the software will never reach th=
e
> end of the software, thus the variable stays set and on next start the
> software sees a set variable and based on this I can decide to disable
> starting the software again. Just blink some leds and go to sleep again.
>
> Anyone did this before? Hopefully I have some time tonight to write the
> software.
>
> Best regards
>
> Peter
>
>
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