As others have already stated, unfortunatly, the bit instructions can only
accept a literal as the bit argument. Just not enough bits in the single word
instruction format to store another variable address.  Just one more trade off
for a 1 cycle per instruction architecture.

I resolved this by writing a macro equivelent for each of the bit instructions
which take a variable as an arguemtn for the bit.  Although these are
implemented
for the PIC17 series of processors, they should be easy to translate for the
PIC16 series.

A CHALLANGE TO THE OTHER MACRAO FANS ON THE LIST, HOW ABOUT EVERYONE POST
THERE
FAVORITE TIME SAVING MACRO!


;Note, variable should contain a number in the range 0..7
;the table lookup will mask out the high 5 bits

vbtfsc  macro   varDataByte,varBitPosition ;test bit position from variable
and skip if bit clear
        movfw   varBitPosition          ;load bit position
        call    BitMaskTbl                      ;convert to bit mask
        andwf   varDataByte,w                   ;isolate bit being tested
        btfss   ALUSTA,Z                        ;Z bit will bet set if bit being
 tested was clear
        endm

vbtfss  macro   varDataByte,varBitPosition ;test bit position from variable
and skip if bit set
        movfw   varBitPosition          ;load bit position
        call    BitMaskTbl                      ;convert to bit mask
        andwf   varDataByte,w                   ;isolate bit being tested
        btfsc   ALUSTA,Z                        ;Z bit will bet set if bit being
 tested was clear
        endm

vbcf    macro   varDataByte,varBitPosition ;clear bit position from variable
        movfw   varBitPosition          ;load bit position
        call    BitMaskTbl                      ;convert to bit mask
        comf    WREG,f                          ;complement mask so we can clear
 bit
        andwf   varDataByte,f                   ;make sure target bit is clear
        endm

vbsf    macro   varDataByte,varBitPosition ;set bit position from variable
        movfw   varBitPosition          ;load bit position
        call    BitMaskTbl                      ;convert to bit mask
        andwf   varDataByte,f                   ;make sure target bit is set
        endm

;You must include this table lookup in your program
;NOTE, INSURE THAT THIS TABKE DOESN'T CROSS A 256 BYTE PAGE BOUNDRY

        org     0x0E00                          ;TABLE MUST BE COMPLETLY CONTAIN
ED IN ONE 256 BYTE MEMORY PAGE
BitMaskTbl
        andlw   B'00000111'                     ;make sure we dont go outside ta
ble bounds
        addwf   PCL,f
        retlw   B'00000001'
        retlw   B'00000010'
        retlw   B'00000100'
        retlw   B'00001000'
        retlw   B'00010000'
        retlw   B'00100000'
        retlw   B'01000000'
        retlw   B'10000000'

At 10:24 PM 99/05/08 -0500, you wrote:
>Hello,   I am trying to use a file register as a mask to clear a bit on
>PORTB. I do get a warning when I compile:
>
> Warning[202] E:\PIC\CODE\test.ASM 113 : Argument out of range.  Least
>significant bits used.
>
>Here is the code:
>Let's say test = 1 for argument's sake (I've tested this and it does)
>  movwf   test           ;save request
>  movlw   .1             ;need to subtract 1 so range is from 0 to 7
>  subwf   test, W        ;w = test - 1
>  movwf   test           ;test = test - 1    test = 0
>  bcf   PORTB, test      ;clear PORTB.0
>
>It doesn't matter what bit I want to clear, bit five is the only one that
>is ever cleared regardless of the value of test. I should point out that
>test is in files register 0x015, so it makes sense why bit 5 (the lower
>nybble) is the only one cleared, but why is it using it's address and not
>it's value?
>
>Thanks, Jay
>
>
Regards

Bob Bullock
KoolKits Electronics Ltd.
bobb@koolkits.com
www.koolkits.com