Hello Ian.

Why not use the same idea as for addition.
At final the Cy=1 if no borrow was taken else Cy=0.

        movfw   Word1Low
        subwf   Word2Low,f

        movfw   Word1High
        skpc                    ;if Cy=1 then simply subwf
        incfsz  Word1High,w     ;if Cy=0 then subwf with borrow
        subwf   Word2High,f     ;if Word1High+1 ==0 then skip SUBWF
                                ;command to save the Cy flag

You may easy to add one more byte subtraction like a second block
in example above.

Be luck in your research ! ;-)

WBR Dmitry.

Ian Parish wrote:
>
> I'm new to this list so this may have been answered before.
> I'm looking for a neat code snippet for word subtract for the 16F84. I've foun
d some info for word add (on Dejanews) but I can't seem to extend this simply to
 subtract.
>
> for word add I've got:-
>
>         MOVF            Word1Low,W
>         ADDWF   Word2Low,F
>         MOVF            Word1High,W
>         BTFSC           STATUS,C
>         INCFSZ          Word1High,W
>         ADDWF   Word2High,F
>
> ... which produces Word2 += Word1, with carry correctly set!
> Any ideas?