You can't use a variable in a BCF.  Here is a simple flow, untested, but the
logic makes sense:

    MOVLW      h'fe'                        ; all bits but 0 set
    MOVWF     work1                    ; mask variable
    MOVFW     position                    ; the bit position
    BTFSC     STATUS,Z                ; if position is zero, the mask is
good
    GOTO      ZBIT
BITLOOP                                        ; roll mask 'position' bits
    BSF     STATUS,CARRY
    RLF     work1,F
    DECFSZ     position,F
    GOTO     BITLOOP
ZBIT
    MOVFW    PORTB                ; PORTB in W
    ANDWF    WORK1,W            ; turn off 1 bit
    MOVWF    PORTB                ; back in port

The same idea to toggle a port:

    MOVLW      h'01'                    ; all bits but 0 clear
    MOVWF     work1                ; mask variable
    MOVFW     position            ; bit position
    BTFSC     STATUS,Z            ; if position is zero, mask is good
    GOTO      ZBIT
BITLOOP                                ; roll mask 'position' bits
    BCF     STATUS,CARRY
    RLF     work1,F
    DECFSZ     position,F
    GOTO     BITLOOP
ZBIT
    MOVFW    PORTB            ; port B in W
    XORWF    WORK1,W        ; toggle 1 bit
    MOVWF    PORTB            ; back in port

I think this is shorter than most examples I've seen.  There is no test for
'position' > 7.

I use similar logic to toggle a static bit:

    MOVFW    PORTB
    XORLW    1<<FIXEDPOSITION
    MOVWF     PORTB



Ed Todd, VP of Engineering <edtodd@sni.net>
http://www.sni.net/cedardell