Ed Sutton <PICLIST@mitvma.mit.edu> wrote:

> I am a PIC 16F8 newbie. One of the first things I was thinking is
> start building an include file containining macros for making
> helpful "extended instructions".
>
> This must have been done a thousand times by PIC experts.

    Actually, no... But it HAS been done a thousand times by PIC
    newbies.

> ;*****************************************
> ;* Macro to assign a literal to a memory location via W
> ;*
> ;* Note: Modifies W register
> '*
> ;*****************************************
> MOVLWF  macro  l, m
>                    MOVLW l
>                    MOVWF M
> endm

    Here's a small list of problems with that, in no particular
    order:

        1.  No one else will know what your non-standard macros do,
        so you'll never be able to post code here without explaining.

        2.  In this specific example, "MOVLWF" is very close to
        "MOVLW" and "MOVWF"; a small lapse of attention while typing
        will result in code that assembles without errors and LOOKS
        approximately correct, but nevertheless fails to work.

        3.  The PIC instruction sets includes a bunch of
        test-and-skip instructions.  Sooner or later, you'll put one
        of them immediately above a multiple-instruction macro, and
        your code will break.  Of course, it'll still assemble
        correctly and look like it should work, so it'll be
        difficult to debug.

        4.  This may never be important to you, but if you ever need
        to perform really extreme optimization on your code, you'll
        want to see each of the real PIC instructions.  The further
        you move from that view -- through macros, compiled C,
        interpreted BASIC, etc. -- the harder it is to optimize.

    There are a number of macros built into MPASM; they're documented
    in the "MPASM User's Guide with MPLINK and MPLIB" (in Table B.11,
    on page 184, of version G).  I'd limit my use of pseudo-opcode
    macros to those, if I were you... But that's just my opinion.

    -Andy

=== Andrew Warren -- aiw@cypress.com
=== Principal Design Engineer
=== Cypress Semiconductor Corporation
===
=== Opinions expressed above do not
=== necessarily represent those of
=== Cypress Semiconductor Corporation

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