>Hmm, problem is,that there is a lot of other interrupts, some of them
>should be as precisely timed as possible. On the processor with normal
>architecture, like Z80(accessible stack in main memory) is not a problem to
>write reentrant interrupt service or there are several interrupt vectors.
>But on PIC it is impossible.

Your original question has already been solved, I guess, but regarding
nested interrupts - although I did not try it yet, IMHO reentrant interrupt
is possible, of course limited by stack and other resources. To preserve
status and W registers, you have to dedicate more memory and still there
will be short moments, when interrupts are disabled. Well, Sinclair is a
different beast... ;-)

Josef