See remars between code
On Mon, Jun 26, 2000 at 11:17:16AM +0100, Russell Farnhill wrote:
> Hi all,
>
> I have just started learning asm and playing around with a 16f84. I've
> already read
> a couple of tutorials from the net and now have a question. How do I create
> a function
> that uses a bit orientated command and pass its arguments via a register. I
> have
> included a small piece of code to try and illustrate.
>
> #include        "p16f84.inc"
> #DEFINE PAGE0 bcf STATUS,5
> #DEFINE PAGE1 bsf STATUS,5
>
> RBpin equ 0x0C          ; Port B pin number
>
>
>         org 4
>         goto start
>
> start
>         clrf    PORTB           ; clear portb
>         PAGE1                   ; select bank 1
>         clrf    PORTB           ; portb all output's
>         PAGE0                   ; select bank 0
>
> loop    movlw   0               ; bit 0 portb
>         movwf   RBpin           ; move bit select into register
>         call    foobar  ; test function
>         goto loop
>
> foobar
>
>         bsf     PORTB,RBpin

What you are doing here is effectively a
        bsf   PORTB,0x0C
So it indeed can't work.

>         return
>
>         END
>
> When I compile this I get the error "Argument out of range.  Least
> significant bits used".
> I guess this is because bsf expects a single bit arg but I pass it a byte. I
> tried loading
> W with my bit number and then read W from within my function which worked
> fine, but if I
> need to pass 2 args I can't use W as one arg overwrites the other.
>
> Any suggestions ?
What I would do is something like :

        RBpin   EQU     0x0C
                                ;bit to set is in RBpin,
                                ; eg. b'00001000'
foobar
        COMF    RBpin,w         ; set b'11110111' in w , complement of RBpin
        ANDWF   PORTB,w         ; make sure bit to set is 0, store in w
        XORWF   RBpin,w         ; make that bit '1' now, store in w
        MOVWF   PORTB           ; set ouput port
return

I hope I got this correct.

There may be a faster (smaller) solution, but can't think of any.

Hans