----- Original Message -----
From: Andrew E. Kalman <aek@PUMPKININC.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Sunday, November 12, 2000 4:56 PM
Subject: Re: [PIC]: 18C452 modify PC not working properly ... ?


> Bob wrote:
>
> >I don't think this will work. If movff won't work directly to PCL, I
doubt
> >it will work indirectly.
>
> Yes, I'm afraid of that, too
>
> >
> >You might try something like this:
> >
> >     push
> >     movwf    PCLATH
> >     movf      TBLPTRL,W
> >     movwf    TOSL
> >     movf       TBLPTRH,W
> >     movwf    TOSH
> >     movf       PCLATH,W
> >     return
>
>
> Yep, I've tried that, but the bad thing about it is that one must
> control interrupts around it. e.g.
>
>
>         bcf     0FF2h,7         ; disable INTs
>         push                    ; required, as we'll undo it with a return
>         clrf    TOSU            ; TOS = jump-to address
>         movff   TBLPTRH,TOSH    ;  ""
>         movff   TBLPTRL,TOSL    ;  ""
>         bsf     0FF2h,7         ; re-enable INTs
>         return
>
> And that still won't work if it's called from within an ISR
> (unintended re-enabling of interrupts). It does work OK otherwise, at
> least in the SIM.
>
> Is it the case that the only instruction that can reliably change PCL
> on the 18 is addwf?


Certainly not!

I've used movwf extensively without trouble, and I'm sure any 'normal'
instruction will give the correct results. It is just that the MOVFF is a
funny case.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

>
>   ______________________________________
>    Andrew E. Kalman, Ph.D.   aek@pumpkininc.com
>
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