        <snip>

> ************
> when i change the bsf code to
>            MOVLW b'00110000'
>            MOVWF PORTB
> it still works
>
        Correct

> **************
> when i change the bcf code to
>             MOVLW b'00000000'
>             MOVWF PORTB
> it still works
> *****************
        Correct

> i wanted to just use 2 registers
> " on " to replace the bsf's
> " off " to replace the bcf's
> but this won't work !!
> =======vars=====
> on    equ    b'00110000'    ;set portb 4 & 5 to 1
> off   equ    b'00000000'    ;set portb 4 & 5 to 0
> ====prog====
> tog        MOVF    on,PORTB ( to replace bsf's)
>
        Bzzzt!! Wrong!  MOVF can move a file either into W or back into the
same file.
        You say you want to use 2 registers to store the two states of the
ports?  Well
        you haven't really defined them properly.  At the moment, you have
two literals:
        on and off that the assembler equates to 0x30 and 0x00 respectively.
Note that
        at the moment you are trying to use these as register locations.

        First you need to define the locations of the registers you want to
use:

        on      equ             12              ; for example...have to
choose your own
        off     equ             13

        Then the contents of those registers need to be set.

        MOVLW   b'00110000'
        MOVWF   on
        CLRF            off                             ; just use a clrf
for off.

        Then you need to move the register into PORTB as before:

        MOVF            on,W
        MOVWF   PORTB

        and:

        MOVF            off,W
        MOVWF   PORTB

        Of course this is assuming that the TRIS register has been set up
beforehand.


        However, this is a bit wastefull, there is no need to use two
registers.  If you need
        to do bit set operations on other pins as well you use a shadow
register.  Call it
        b_shadow:

        on                      equ             b'00110000'
        off                     equ             0
        b_shadow        equ             12


        To set 'on'

        MOVLW   on
        MOVWF   b_shadow
        MOVF            b_shadow,W      ; don't actually need this in this
case
        MOVWF   PORTB

        Of course this is a bit long winded, but the beauty of this is that
you can now do
        bit operations on the shadow register without worries:

        BCF     b_shadow,0
        BSF     b_shadow,4
        MOVF    b_shadow,W
        MOVWF   PORTB

        Hope this dosen't confuse you any more...

        Regards

        Mike Rigby-Jones

>            MOVLW   0x04
>            MOVWF   togh
> delh       DECFSZ  togh
>            GOTO    delh
>
>            MOVF    off,PORTB (to replace bcf's)
>            MOVLW   0x02
>            MOVWF   togl
> dell       DECFSZ  togl
>            GOTO    dell
>
>            BTFSC   PORTB,3     ;skip next if 0 , checks for 0 ac cycle
>            GOTO    tog
>            RETURN
>
> there's no o/p's at all !
>
> i also wanted to use 2 registers for the literals too
> togh    equ    0x04
> togl    equ    0x02
>
> thanks for your advice
> glen