Thanks Myke, Baz and Stephen for your feedback:

>Yes - I've tried the Lennard Research #149.00 4MHz real-time
>emulator called TRICE.

I found Lennard Research's info after sending the message, and it looks like
great value. Their blurb indicates that multiple PICs are used to mimick a
PIC in software, with the program stored externally in 8k of RAM.

I'm aiming to fit a resident monitor (including serial I/O) into a small part
of the program memory as an interrupt routine, so the application program can
run in the chip as normal. Clearly, this approach would only be sensible for
an EEPROM-based (must get used to saying Flash-based) PIC, so is confined to
the '84. Not really an emulator, more a debugger - but running in-circuit.

>Unfortunately, the PIC architecture is really not well suited to simple
>emulators/monitors (debuggers).

Which is what I'm wanting to do, and I see what you mean. Still, I'll plod on
...

Andy.