Jim, sorry for the late reply. I noticed that you also use the Parallax
assembler. First note that it has been updated as CVASM and is available as
part of the commercial TDE package from Tech Tools. The assembler is free
and now includes support for the 16C76/77 and a few other enhancements. You
can assemble your Parallax code `as-is'. To update to CVASM, download the
TDE demo from:

      http://www.tech-tools.com

   Back to interrupts and 16C73/74/76/77 devices, I normally use the example
from the 16C7x data book. Obviously you will want to modify it to suit your
application. The following is a `Parallax-friendly' ISR `wrapper' in mostly
Microchip syntax:

;       Bank 0 Registers

        ORG     20h

W_copy  DS      1               ; Copy of W Reg for Interrupt Handler
S_copy  DS      1               ; Copy of STATUS Reg for Interrupt Handler
PCHcopy DS      1               ; Copy of PCLATH Reg for Interrupt Handler
FSRcopy DS      1               ; Copy of FSR for Interrupt Handler

; Clone W_copy as the first byte in each bank:

        ORG     20h             ; Bank 1, etc...

W_copy1 DS      1

   The last line assumes SPASM v4.7 or earlier. With CVASM, you can use:

        ORG     0A0h            ; Bank 1, etc...

; Interrupt Handler

        ORG     4

        MOVWF   W_copy          ; Copy W to temp
        SWAPF   STATUS,W        ; Swap STATUS to be saved in W
        CLRF    STATUS          ; Switch to Bank 0
        MOVWF   S_copy          ; Copy STATUS to temp
        MOVF    PCLATH,W        ; Copy PCLATH to temp
        MOVWF   PCHcopy
        CLRF    PCLATH          ; Switch to Page 0
        BCF     STATUS,7        ; Point IRP to Bank 0
        MOVF    FSR,W           ; Copy FSR to temp
        MOVWF   FSRcopy

        [Your ISR...]

        MOVF    FSRcopy,W       ; Restore FSR
        MOVWF   FSR
        MOVF    PCHcopy,W       ; Restore PCLATH
        MOVWF   PCLATH
        SWAPF   S_copy,W        ; Restore STATUS
        MOVWF   STATUS
        SWAPF   W_copy,F        ; Restore W
        SWAPF   W_copy,W
        RETI

   Mike Keitz pointed out other `gotchas' and suggestions:

>* Store PCLATH (in page 0) and reset it to 0 before goto, call, etc.  The
>  conventional approach needs 5 instructions and 1 byte RAM.
>* Don't let an interrupt occur while PCLATH is out of page 0.
>* Don't use any gotos, calls, or PCL modifies in the ISR.
>* Put identical copies of all ISR routines that are the target of goto,
>  call in all code pages.  Seems like the best way to do this would be to
>  write the ISR as a macro and place it at 0x004, 0x804, etc.  Uses lots of
>  code space but no time or RAM.

   - Tom

At 02:14 PM 5/19/98 -0700, Jim/jhobbs wrote:
>Here is something I have been doing with the 73.
>
>Given that an interupt can occur at any given time, and code execution could
>be taking place on any page and working with any bank.
>What does this mean?
[snip]
>
>Take care  -jim