Martin J. Maney <PICLIST@MITVMA.MIT.EDU> wrote:

> > [Quoting me:]
> >
> > Sorry you wasted half a day on this.  An easier way is the
> > following, which is on my web page and has been in the Microchip
> > data books for a couple of years now:
> >
> >     INTW    EQU     [any page-0 register]
> >     INTS    EQU     [any page-0 register]
> >             ....
> >     ; INTERRUPT SERVICE ROUTINE:
> >     PUSH    MOVWF   INTW                    ;SAVE THE W-REGISTER.
> >             SWAPF   STATUS,W                ;SAVE THE STATUS
> >             MOVWF   INTS                    ;REGISTER.
> >             <interrupt handler runs here>
> >     POP     SWAPF   INTS,W                  ;RESTORE THE STATUS
> >             MOVWF   STATUS                  ;REGISTER
> >             SWAPF   INTW                    ;RESTORE THE
> >             SWAPF   INTW,W                  ;W-REGISTER.
> >             RETFIE                          ;RETURN AND RE-ENABLE
> >                                             ;INTERRUPTS.
>
> Okay, this is pretty simple (although I don't recall noticing that
> it isn't necessary to use swapf to transfer the STATUS register
> until you helpfully pointed that out).  Now, how does one do this
> for a PIC where the register page select actually changes the
> (general purpose) register that an instruction addresses?

Martin:

That one's also on my web page.  It looks like this:

    INTW    EQU     [any page-0 register]
    INTS    EQU     [any page-0 register]
    INTW1   EQU     INTW + 080H

            ....

    ; INTERRUPT SERVICE ROUTINE:

    PUSH    MOVWF   INTW
            MOVF    STATUS,W
            BCF     STATUS,RP0
            MOVWF   INTS
            ; save PCLATH and FSR here.

            ....

    POP     ; restore PCLATH and FSR here.
            MOVF    INTS,W
            MOVWF   STATUS
            SWAPF   INTW
            SWAPF   INTW,W
            RETFIE

-Andy

Andrew Warren - fastfwd@ix.netcom.com
Fast Forward Engineering, Vista, California
http://www.geocities.com/SiliconValley/2499