>How deep is the stack for calls/returns?  This is on an 877 device

Well the RTFM for the stack is 8 levels, of which one will be used for the
interrupt itself.

and if you use Olin's great development environment, he has included all the
necessary code to save and restore all necessary registers when entering and
leaving an interrupt routine, no matter what page the background code is in.
There is a certain amount of RTFM in this as well, as there are a number of
notes around that cover the necessary code to do the save and restores.
Check the PIC archives if all else fails.

You should seriously get Olin's PIC development code, as it gets rid of many
of the chores related to bank and page switching if you use the macros
sensibly.

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