Hello Jean-Michel.

As far as I understand you need I can see two ways to do it.

1. You only need to shift single one register.

        rlf     byte1,W         ;get new bit from carry

        xorwf   byte1,W         ;get difference
        andlw   B'00011111'     ;0's will mask unchanged bits
        xorwf   byte1,F         ;update only required bits

2. You need to shift in such way through many registers.

        rlf     byte1,W         ;get new bit from carry
        andlw   B'00111111'     ;mask msb's but last
        addlw   B'11100000'     ;copy last to carry

        xorwf   byte1,W
        andlw   B'00011111'     ;see explanation of
        xorwf   byte1,F         ;this in example above
;then
;
        rlf     byte2,W
        andlw   B'00111111'
        addlw   B'11100000'
;
;and so on as many bytes as you need ;)


WBR Dmitry.



> I need to shift a 5 bit number in, through and out of a byte using bit0 to
> bit4 and not affect bit5 - bit7.
>
> The best way I can think of an example is if you had two 8 bit wide
> registers next to each other like the following.  The 5 bit value in byte 2
> is shifted left throughout byte 1 and out.
>
> byte1     byte2
>
> XXX00000  xxx11111      start state
> XXX00001  xxx11110
> XXX00011  xxx11100
> XXX00111  xxx11000
> XXX01111  xxx10000
> XXX11111  xxx00000
> XXX11110  xxx00000
> XXX11100  xxx00000
> XXX11000  xxx00000
> XXX10000  xxx00000
> XXX00000  xxx00000      end state
>
> Only byte 1 is important, byte 2 is just for my example.
>
> X = can not be changed, x = not used

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