At 11:41 30/04/98 -0500, you wrote:
>Can I control where execution resumes after an external interupt on the 16C63?
>I want to start at the head of the main loop, but not lose my current
>variables.
>
>Can I, and if so, How?
>
>Thanks,
>
>John C.
>John A. Craft

The main difference between PIC16C84 and PIC16C63 is RAM page,
PIC16C63 has 2 RAM pages with no common byte between the two
pages. So when an interrupt occurs, STATUS page bit is unknown
and you are obliged to store first W register, and after
STATUS, so W Register will be store in 0x20 ###or### depending
of STATUS page bit in 0xA0. The problem does not appear with
16C84 as RAM in page 1 is remapped in page 0.
Here the code for INT:


INTW      equ 0x20               ; Must be RESERVED ALSO in PAGE 1 !! (0xA0)
INTStatus equ 0x21               ; as STATUS bit page is unknown when interrupt
                                 ; occurs

           org 0x0004

           movwf INTW            ; Save W and Status registers
           swapf STATUS,W
           bcf STATUS,5          ; Clear page BIT
           movwf INTStatus

; Place here the code for your interrupt

                                 ; ---------- END OF INTERRUPT ----------------
IntrEnd:
           swapf INTStatus,W     ; Restore W and Status registers
           movwf STATUS
           swapf INTW
           swapf INTW,W
           retfie

Regards,
        Philippe.

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