On Sun, 27 Jul 1997 12:16:05 -0700 "'Grif' w. keith griffith" writes: >At 00:10 7/27/97 +0000, you wrote: >>We have been building a unit that uses commercial 16C54A in an >application >where >>it can get hot. We tested several of the first units and they worked >>well up to 200 degrees F and thought we were in good shape. >>Now we were testing another part of the project and are suddenly >>seeing failure at temperatures of about 140 deg F. >> > >Did you look at the 5 volt supply at the higher temps? 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.