'It's a newbie thing' , as they say.

I turned off the enthusiasm and got down to reading the documentation.

The PORTH - PORTC define is a non-issue, as you say Bruce. PORTC is referenced as PORTC in the 16F68x.inc file, correctly.

The error was that I didn't notice the section of the manual dealing with interrupts for when the target device has more than 2K of codespace - I have added my own interrupt handler stub when PBasic has added one for me already. Consequently, when my stub runs after Pbasic's stub W is actually saved as the last action of the PBasic stub, and not the last value of the runtime code. Also there may have been another error with my restoration of the context registers, but I couldn't check it - I blew away and re-wrote the assembler interrupt stub completely and now it runs just as expected.


Thanks to everyone for their suggestions.

RTFM, as they say.........

Chris