> > In your case you will be actively stomping on PCLATH in the interrupt in
the
> > table lookup code, so you have to save/restore it.
>
> But only if PCLATH is used outside the interrupt routine too, otherwise
> I can stomp on it all I like, right?  (Same should go for FSR, and even
W).

All true, but unless you really really really need every last cycle this is
a bad idea.  If you aren't doing a table lookup or computed GOTO and are on
a processor with a single code page, you could in theory trash PCLATH in the
interrupt routine.  Trashing FSR is slightly more dangerous because you are
more likely to use it without thinking about it, like an implicit software
stack operation.  Unless the foreground program does nothing (everything is
done in the interrupt), you will need to save W.

All these things are very dangerous because they are bugs just begging to
happen.


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