Hi Bob,

I haven't worked through your code with pencil and paper but skiming=20
through it it does look good :-)

Regards
Sergio


On Mon, 7 Aug 2017, Bob Ammerman wrote:

> NOTE: all numbers are in HEX below. The trick below
>   works because we are working MODULO 100 hex.
>
> Input:   W is a pointer ranging from 00h thru 9Fh
> Output:  W points to the correct register in bank 0 or 1
>
> ; At entry, the value of W is as follows:
> ;  00..4F - we want to map to page 0 addresses 20..6F
> ;  50..9F - we want to map to page 1 addresses A0..EF
>
> ; We start by adding B0. This will set STATUS,C to 1,
> ; if we have a page 1 address, and to 0 if we have a
> ; page 0 address. After this add, we will have:
> ;  B0..FF - which we want to map to page 0 addresses 20..6F
> ;  00..4F - which we want to map to page 1 addresses A0..EF
>
>   ADDLW 0B0h
>
> ; Now, if carry is set, we add 30. After this conditional
> ; add, we will have:
> ;  B0..FF - which we want to map to page 0 addresses 20..6F
> ;  30..7F - which we want to map to page 1 addresses A0..EF
>
>   BTFSC STATUS,C
>   ADDLW 030h
>
> ; One more add gives us our answer. By adding 70 we get:
> ;  20..6F for page 0 addresses
> ;  A0..EF for page 1 addresses
>
>   ADDLW 070h
>
> -- Problem solved in 4 instructions!
>
> ~ Bob Ammerman
> RAm Systems
>
> --=20
> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist
>
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.