On Wed, 15 Aug 2001, wouter van ooijen & floortje hanneman wrote:

> >     swapf    w,0
>
> The first argument of swapf must be a file register. W is not a file
> register, so this does not work. The assembler will accept it, because w and
> f are just symbolic equivalents for the 0 and 1 that are used to specify the
> destination. Try "swapf f,0": it will be accepted by the assembler for the
> same reason that "swapf w,0" is accepted.

Just to be clear,

    swapf    w,0

is equivalent to:

    swapf    INDF,W

Since W and INDF are both equ'd to 0.

If you want to swap the nibbles in W then you'll need to do something
like this:

    movwf    temp
    swapf    temp,W


(Unless you're using the 18cxx in which case you can write
    swapf    wreg0,w
)


If you want to shift W left 1 space then:

    movwf    temp
    addwf    temp,w

( a rlf will pick up the carry, but otherwise work just as well)


Shift left 2:

    movwf    temp
    addwf    temp,f
    addwf    temp,f
    addwf    temp,w

Or
    movwf    temp
    rlf      temp,f
    rlf      temp,w
    andlw    0xfc      ;Clear garbage shifted in


Scott

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