Rolf wrote:

>         ORG     0x004             ; interrupt vector location
>         movwf   w_temp            ; save off current W register contents
>         movf    STATUS,w          ; move status register into W register
>         movwf    status_temp       ; save off contents of STATUS register
>

They key point here (and also what I *think* that Tamas
has got wrong) is that MOVWF does *not* change the Z-flag.
It doesn't change any STATUS flags. Thats why the code
*does* work, even without any SWAPF's in the code above.

Below, OTOH, SWAP *must* be used, since MOVF (either to "W"
or to "F") *does* set/clear the Z-flag.

Jan-Erik.


> 
> ; isr code can go here or be located as a call subroutine elsewhere
> 
> 
>         movf    status_temp,w     ; retrieve copy of STATUS register
>         movwf    STATUS            ; restore pre-isr STATUS register 
> contents
>         swapf   w_temp,f
>         swapf   w_temp,w          ; restore pre-isr W register contents
>         retfie                    ; return from interrupt
> 

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