Bjarne Nebelong <PICLIST@MITVMA.MIT.EDU> wrote:

> What I need is:
>         #1 Read in port for 5 bits.
>         #2 Jump according to the in value.
>         #3 Do some bit manipulation.
>         #4 return to #1
>
> In 87C750 I have done like this:
>
> loop:
>         mov     A,P1            ;P0.0 always zero
>         mov     DPTR,#JumpTable
>         jmp     @A+DPTR
>
> JumpTable:
>         ajmp    A0  ;000000
>         ajmp    A1  ;000010
>         ..
>         ajmp    A31 ;111110
>
> A0:
>         anl     p3,#00111000b   ;clear bit 0,1,2
>         nop
>         nop
>         orl     p3,#00111000b   ;set bit 3,4,5
>         ajmp    loop
> ..
>
> How can I make this possible in the 16C54 (cheapest I could
> find)???

Bjarne:

A direct translation of your program looks like this:

    LOOP:

             MOVF    PORTB,W         ;GRAB THE VALUE ON THE PORT.
             ANDLW   00011111B       ;MASK OFF ALL BUT THE LOW 5
                                     ;BITS.

             ADDWF   PC              ;JUMP TO TEH APPROPRIATE ELEMENT
                                     ;IN THE JUMPTABLE.

    JUMPTABLE:

             GOTO    A0                         ;PORT = xxx00000.
             GOTO    A1             ;PORT = xxx00001.
             GOTO    A2             ;PORT = xxx00010.
             ....
             GOTO    A31            ;PORT = xxx11111.

    A0:

             MOVLW       11111000B      ;CLEAR BITS 0,1 AND 2.
             ANDWF   P3             ;
             MOVLW   00111000B      ;SET BITS 3, 4, AND 5.
             IORWF   P3             ;

             GOTO    LOOP           ;LOOP BACK.

This isn't the most efficient way to do perform the task, but it'll
work just fine.  The only thing to remember is that the entire
jump-table (from "JUMPTABLE:" to "A0:") must be located in page 0
(addresses 000-0FF), since the "ADDWF PC" produces only an 8-bit
result.

-Andy


=== Andrew Warren - fastfwd@ix.netcom.com                 ===
=== Fast Forward Engineering - Vista, California          ===
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