Alan B. Pearce wrote:

> > So, for a solution try this:
> >
> > 0204  bitnum
> >                    rlncf  WREG   ;Double offset for PIC18 family only.
> >                    addwf   pcl            ;
> >                    retlw    0x01
> >                    retlw    0x02
> >                    etc
>

> First doing a rotate can be a bad way to do it, because you first need to
> clear the carry bit.

Note the use of RLNCF "rotate left no carry".
                                   --

On the other hand, you must make sure that bit 7 is clear !
So begin with an 7-bit, right justifyed index...


> Note that in Jinx's code he stores W in a variable anyway, so the easier way
> of doubling the value is the following code line
>
>      addwf    temp,w    ; value of w already in temp, so w = 2*w
>                         ; no need to clear carry first

Don't need the temp variable :

      addwf    wreg,w     ; add W and WREG, store in W. (add W to itself)

      (Does this work ???)

> and then the following code allows a greater than 256 (16 family) or 128 (18
> family) entries
>    btfsc    status,c    ; has doubling w set carry flag?
>     incf    PCLATH        ; assume PCLATH already set to correct value
> before entering here


How can you have a table larger then 256 entries, if you begun with
an 8-bit "index" in the first place ? Well, you could, but only accessing
the even (or odd) entries, I'd guess...


> However as
> someone else pointed out both the size restriction and the page boundary
> restriction can be removed by doing a full 16 bit calculation...

... and to have more then 256 *usuable* table entries at all, not ?

Jan-Erik.

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