> ... This all works just fine, but now and then I wish the architecture
would
> allow the bit-ordinal value to be expressed in 'W', (i.e. as a "computed"
> value, rather than a compiled constant in the code), so I could do
something
> like:
>
> btfsc    FLAGS, W     ;  (NOT a valid instruction :^(
> ...
>


This one is a perennial question. Check the archives:


Basic technique:


; turn on a bit
    call      get_bitmask
    iorwf   FLAGS,F

; toggle a bit
    call      get_bitmask
    xorwf   FLAGS,F

 ; turn off a bit
    call    get_bitmask
    xorlw    0xFF
    andwf    FLAGS,F

; sub to get the mask

... make sure PCLATH is right, look out for page crossing ...

get_bitmask:
    addwf    pcl,f
    retlw     1
    retlw     2
    retlw     4
    retlw     8
    retlw    16
    retlw    32
    retlw    64
    retlw    128

Bob Ammerman
RAm Systems

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.