Dear Sam Woolf,

sam woolf <samw@COGS.SUSX.AC.UK> on 2001-05-07 09:51:05 AM wrote:
> 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

Since this code needs to focus on just that one pin, you need to use AND to mask
off all the other pins.
Also, try using "movlw" to move (compile-time) ``literal'' constants to w;
try using "movfw" to move (run-time) variables to w.

  ; Warning: untested code
...
  movlw PIN0
  movwf current_pin
...
wait_for_lo:
  call increment_hi_time_counter
  movfw PORTA
  andwf current_pin,w
  skpz
  goto wait_for_lo
...
wait_for_hi:
  call increment_lo_time_counter
  movfw PORTA
  andwf current_pin,w
  skpnz
  goto wait_for_lo
...

Isn't there a timer/counter on your PIC ? Perhaps the software would be simpler
(and the timing more accurate) if you used that timer/counter on the PIC, and
added external mux hardware to switch the appropriate signal to the PIC's timer
pin.

Sounds like you're working on a little robot with sonar sensors.
I'd enjoy looking at a web page with the source code and a couple of small
photos.
(There's lots of "free" sites out there
  The 100 Best Free Web Space Providers Reviewed
  http://100best-free-web-space.com/Top100.htm
or you could talk James Newton into letting you put them on piclist.com).


--
David Cary

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