On Sun, 9 Oct 2005 13:14:20 +0100, you wrote:

>PIC18F8621 on my board stores in memory some counters. I would like to be
>able to preserve these counters even after power loss without saving it in
>EPROM.
>
>Is this possible to have two power sources on one board simultaneously?
>
>I found round batteries which are 3.3V but I can't find 5V ones and my PIC
>is 5V. Does anybody know such batteries?

..but the PIC does not need 5v just to keep the counter values. 
Set it up with a couple of diodes so that when power fails, supply to just PIC  is fed from the
battery source, and have an interrupt or other signal to tell the PIC power has failed so it can
turn off any outputs that drain current and go to sleep mode. 

-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist