Agreed that I made limit a register, as
he defined it that way in his macro.

It should be addlw 1, yes.


--Bob



----- Original Message -----
From: "Scott Dattalo" <scott@DATTALO.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Sunday, December 01, 2002 2:47 PM
Subject: Re: [EE]: PIC 12C508A


> On Sun, 1 Dec 2002, Bob Axtell wrote:
>
> > In standard binary arithmetic, the SUB function can
> > be substituted by the NEGate function followed by
> > an ADD.  NEG is also not part of the 12C08 instructions,
> > so to do that, complement and increment the result by 1.
> > The carry will set if (negate of reg) + (limit) overflows, which
> > corresponds to subtracting limit from reg > w.
> >
> > In the following PIC12C508A code, if limit is set to d'10', reg
> > will count to 9 then go to 0.
> >
> > inccmp  macro    reg, limit
> >          incf    reg,f
> >          comf    reg,w
> >          incf    w
> >          addwf   limit,w
> >          btfss   status,c
> >          clrf    reg
> >         endm
>
> This clearly will not work. First, W is not a register (you'll need an
> 'addlw 1' instead of an 'incf w') and second, the original poster was
> comparing "reg" to a constant "limit". One other subtle issue is that the
> original macro would return if reg was greater than limit.
>
> Fortunately, Eke's problem is solved with a 'subwf':
>
> inccmp  macro    reg, limit
>      incf   reg,F
>      movlw  limit+1
>      subwf  reg,W
>      skpc
>       return        ; reg is less than or equal to LIMIT
>      clrf  reg      ; reg is greater than LIMIT
>
>   endm
>
> This changes the comparison from an A-B to a B-(A-1) and looks at the
> opposite state of the carry flag.
>
> Scott
>
>
> >
> > --Bob
> >
> > ----- Original Message -----
> > From: "Eke Neehr" <ake.neehr@TELIA.COM>
> > To: <PICLIST@MITVMA.MIT.EDU>
> > Sent: Sunday, December 01, 2002 10:01 AM
> > Subject: [EE]: PIC 12C508A
> >
> >
> > Hello!
> >
> >
> > For a Pic 16F84 device I have this
> > macro routine:
> >
> > inccmp  macro    reg, limit
> >                incf         reg, f
> >                movf       reg, w
> >                sublw      limit
> >                btfsc       STATUS, C
> >                 return
> >                clrf          reg
> >                endm
> >
> > but for the 12C508A device the instruction
> > sublw don4t exist.
> > Can any kind person tell me what I have
> > to take for instructions to get the same function!
> >
> > Regards
> > EkeN
> >
> > --
> > http://www.piclist.com#nomail Going offline? Don't AutoReply us!
> > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body
> >
> > --
> > http://www.piclist.com#nomail Going offline? Don't AutoReply us!
> > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body
> >
> >
> >
>
> --
> http://www.piclist.com#nomail Going offline? Don't AutoReply us!
> email listserv@mitvma.mit.edu with SET PICList DIGEST in the body
>
>
>

--
http://www.piclist.com hint: To leave the PICList
mailto:piclist-unsubscribe-request@mitvma.mit.edu