On 21/02/2015 12:59, IVP wrote:
> Hi all,
Hi joe,

> Can I make PCLATH advance to 0x02 if (W + PCL) > FE
> under any circumstances (ie wherever code happens to be)
>
> For example, if I execute
>
>          movff   pcl,temp0  ;eg PCL =3D 0xD8
>
>          addwf   temp0  ;result of W * 8
>          skpnc
>          incf    pclath
>
> after the rlncf's, it seems to work. But seems a bit inelegant and
> might not work as code is moved/edited
the incf will works ever because the jump will stay in a 256 byte boundary.

> I have plenty of code space and can org the mode routines to just
> after a boundary so that they all have a common PCLATH but
> that seems a bit crude. Or org the computed branch as a subroutine
> after the main code (as you might for a table etc) rather than
> embedding it in-line
I left long ago the use of an ORG for this kind of things, I think that is =
safer
to do right calculation to maintain the code relocatable.
The only problem will arise if you need also to check the 64kB boundary and=
 use
PCLATU. I usually leave a comment to warning.

I would change exactly like Christopher, with only one difference (find it!=
):

        movlw  high(mode0)
        movwf  pclath
        swap    portc,w             ;multiply * 16
        rrncf    wreg,w              ;divide by 2
        andlw  0x78                   ;mask for 0x0f * 8
        addlw  low(mode0)     ;calc dest address and store to W
        skpnc
        incf      pclath,f        ;remember PCLATU
        movwf   pcl            ;jump


                Nic

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