Dave Birchall posted a hex-to-ASCII routine that I wrote and
asked about my use of the BNC pseudo-op.

Mike Ghormley <PICLIST@MITVMA.MIT.EDU> replied:

> BNC is a pseudo-op which stands for Branch on Not Carry. It will
> branch the code to a LABEL if the Carry Flag is NOT set.

    Correct.

> IMHO the code that you posted doesn't work.  It would loop forever.

    Incorrect.

> I have added code that I believe will do the job.  I have denoted
> my code additions it by placing "@@@" in the expanded comments.
>
> ;@@@ equates for the destination register for operations so that we
> ;@@@ can use code such as:
> ;@@@    SUBWF   REGISTER,w
> ;@@@ or
> ;@@@    ADDWF   REGISTER,f
>         w       EQU     0       ;@@@ destination is the working reg
>         f       EQU     1       ;@@@ destination is the file reg

    This is unnecessary; any assembler that understands the "BNC"
    pseudo-op also understands the "w" and "f" destination-specifiers
    without any need for them to be explicitly defined.

    Furthermore, the "improvements" you made to my code do nothing
    but make the code slower and larger.  For the sake of
    readability and brevity, I'll show just one portion of your
    version without the lengthy comments, rather than quoting the
    whole thing verbatim:

    Michael's version:
    ------------------

>   DO100S  MOVLW   d'100'
>           SUBWF   ASCIIO,w
>           BNC     DO10S
>
>           INCF    ASCIIH,f
>
>           MOVLW   d'100'
>           SUBWF   ASCIIO,f
>           GOTO    DO100S

    My original code:
    -----------------

    DO100S  MOVLW   100
            SUBWF   ASCIIO,W
            BNC     DO10S

            MOVWF   ASCIIO
            INCF    ASCIIH
            GOTO    DO100S

    Ok... If you look closely at my code, you'll see that after the
    BNC instruction, the W register ALREADY contains ASCII0-100;
    there's NO NEED to load W with 100 and do the subtraction again.

    That is, contrary to the comments you wrote for my code, the
    result of the subtraction IS used.

    -Andy

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