> If you're using window EPROM chips be sure to erase them thoroughly (3 or
> 4 times the dose that makes them "blank") before reuse.  Marginal erasing
> can cause wrong instructions to be read at extremes of operation.  A bad
> instruction could make the PIC do most anything, including corrupt the
> RAM.  The erase margin can be stressed at room temperature by lowering
> the supply voltage.


That would explain the problem that I have been having with parts in a
3V circuit!  Sometimes I get a part that will not run after having
programmed successfully.  I erase the part and re-program and it works
fine.  It was probably not completely erased.

Bill