> -----Original Message-----
> From: sam woolf [SMTP:samw@COGS.SUSX.AC.UK]
> Sent: Friday, May 04, 2001 1:36 PM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [PIC]:a newbie mpasm question
>
> Hi everyone. Sorry if this is a silly question.
>
> I have a subroutine called PULSE that oscilates one of the pins on the
> 16F84. It does this by using BCF and BSF to set and clear that pins bit on
> porta.. so basically there are some loops and instructions like
> BCF PORTA,1
>
> My question is: how can I modify my subroutine so that I can set which pin
> to oscillate. I want to be able to do something like:
>
> movlw     1; load w with number of pin on porta to pulse
> call    ping; oscillate pin 1
> movlw    2;now load in new pin number
> call    ping ;    oscillate pin 2.
>
> How can I do this? Are instructions like BCF porta,w valid? I've tried
> this and it doesn't seem to work.
> Any suggestions much appreciated.
> sam.
>
That instruction is not valid, the bit must be set at compile time.
One way of doing this is to use a lookup table to convert your bit number to
a mask

e.g.

GetMask:
        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'


Then use the returned bit mask to toggle the port:

movlw 1                         ; select pin to toggle
call GetMask            ; retrieve the appropriate mask
xorwf PORTA,f           ; toggle the pin

Everytime you XOR the port with the mask, the select bit will toggle.

Hope this helps.

Mike

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