Simon Nield wrote:
> the problem:
> i need to biphase code a byte for serial transmission over an rf link.
> in other words each '1' becomes '10' and each '0' becomes '01'.
> if it makes the code easier then '1' becoming '01' and '0' becoming '10=
'
is ok too.
> =

> this _could_ be done with a lookup table, which would be fast, but that=
's
not the point of a tiny
> code challenge now is it ?

Is there any particular requirement that the bits be sent in their origin=
al
order?  If not, send every other bit on each pass - that way, you don't
have to shift them as far from their original location.

        movf    byte_to_send,w  ;abcdefgh
        andlw   b'01010101'     ;0b0d0f0h
        movwf   temp
        clrc
        rlf     temp,w          ;b0d0f0h0
        iorwf   temp,w          ;bbddffhh
        xorlw   b'10101010'     ;BbDdFfHh
        call    send_byte

        movf    byte_to_send,w
        andlw   b'10101010'
        movwf   temp
        clrc
        rrf     temp,w
        iorwf   temp,w
        xorlw   b'10101010'     ;AaCcEeGg
        call    send_byte

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