thankyou Michael, that works. Now a related question:
I have a subroutine called ECHO that listens for and times highs and lows on
one pin of the 16F84..
The original code uses BTFSS PORTA, PIN
I want to be able to set which pin to listen to from outside the subroutine.
I've tried to do a mask thing, but it doesn't work:
basically I replaced BTFSS PORTA, PIN
with:
PIN0    EQU    B'00000001'
PIN1    EQU    B'00000010'
;
MOVF        PIN0,W
XORWF      PORTA
BTFSS        STATUS,Z

  This doesn't seem to be working? Any idea why not? Is there anything else
I can try?
sam


----- Original Message -----
From: "Michael Rigby-Jones" <mrjones@NORTELNETWORKS.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Friday, May 04, 2001 2:00 PM
Subject: Re: [PIC]:a newbie mpasm question


> > -----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
>
> --
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>
>

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