myke predko wrote:

> This is an eight bit subtract of a 24 bit value, but you are not
> bringing the carry to the most significant byte ("t2").

and Scott Dattalo <PICLIST@MITVMA.MIT.EDU> replied:

> If you wanna do this why not do it like:
> ....
>
>   movlw d'1000000'&0xff
>   subwf t0,f
>   movlw 1
>   skpnc
>    subwf t1,f
>   skpnc
>    subwf t2,f

Scott:

After reading the recent "commenting practices" thread that was
sparked by Myke Predko's use, with no explanatory comments, of the
FSR as a generic temporary variable (and worse, if you recall, he
used the temporary variable in ALMOST the same way that the FSR is
usually used), I think I'd rewrite your code like this:

    LIST    P=16C54,R=DEC

    MOVLW   1<<6        ;No need for "&0xff", since 1000000 = 1E6.
    SUBWF   T0,TMR0     ;TMR0 has just overflowed.
    MOVLW   F           ;W register = F (just F, not 0x0F).
    BTFSC   STATUS,W    ;Skip if C (just C, not 0x0C) = W.
    SUBWF   T1,W+1      ;(W register = F still, but W = F-1).
    BTFSC   STATUS,INDF ;We're using INDF and FSR together
    SUBWF   T2,(FSR-3)  ; here, but not in the usual way.

This code assembles identically to yours... But since it's fully
commented, it's clearly better.

-Andy


=== Andrew Warren --- aiw@cypress.com
=== IPD Systems Engineering, CYSD
=== Cypress Semiconductor Corporation
===
=== Opinions expressed above do not
=== necessarily represent those of
=== Cypress Semiconductor Corporation

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