On Fri, 6 Nov 1998 07:37:54 -0000, you wrote: >Dale Wescombe wrote: >> I can program a DIP package PIC16C73 with the same code and put it the >> same circuit and it works fine. >> >> I can use an older SO-28 PIC16C73A (batch 9731SBN) with the same code >> and put it in the same circuit and it works fine. >> >> I program a PIC from either of the two new batches and it fails to >> function at all. I have tried them in two versions of our PCBs, in a > >Sounds like a classic case of an uninitialized RAM location. The contents >are never guaranteed, but in a given batch they tend to have similar >behavior, so this kind of situation can result. > >Cheers, >Eric I'd agree this is the most likely cause (in which case you've just been lucky in the past), but oscillator problems can also vary from chip to chip, especially with ceramic resonators - if there's too much capacitance between the osc pins, startup can become unreliable. Try sticking a 10M resistor across the osc pins.