> The program works (at least it has been working for the last year and on
> about 100 other boards), changing the 17c756 brings it back to life, so my
> question is could the PIC be destroyed in such a way as to just affect the
> uart or a particular register such as SPBRG1?

Yep.

> I've fixed the thing for now with a replacement PIC but can anyone possibly
> enlighten me about what they think it might be?

Single-bit failures in memory used to be fairly common.  That's what you
have -- a single-bit failure in one register.  It happens.  As to why - I
dunno, bad phase of the moon, holding your tongue wrong when it was
programmed, not enough pepper on the chicken, who can say?

Dale

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