;
; ***************************************************************************
; ***  Bubble Software Parallax to PIC Source Converter. Copyright 1999.  ***
; ***  http://www.picnpoke.com                 email: sales@picnpoke.com  ***
; ***************************************************************************
;
; POT
; This program shows a technique for reading resistance. The pot input pin can
; only be changed during assembly, not once the program is running.

	P = pic16c55
	#include <16c55.inc>   ; processor assembler definitions
	_CONFIG _xt_osc & _wdt_off & _protect_off
 reset start

 org 8
temp Res d'1' ; Temporary counter for delay.
potL Res d'1' ; Low byte of Pot measurement.
potH Res d'1' ; High byte of Pot measurement.
pot equ  ;ra.0 Pin assigned to pot.
out_pot equd'0'  ; Value to set ra.0 to output for pot.
in_pot equd'1'  ; Value to set ra.0 to input for pot.

 org 0
start        MOVLW out_pot              ; RA.0 to output.
             TRIS 5h
             MOVLW d'0'                 ; All outputs for LEDs.
             TRIS 6h
             BSF 5h,d'0'                ; Start charging cap.
             MOVLW d'8'                 ; Set up for 6-ms delay: 8 trips
             MOVWF potL
start_wait   DECFSZ temp                ; through outside loop x 256
             GOTO start_wait
             DECFSZ potL                ; x 3 cycles for inside loop = 6.1 ms.
             GOTO start_wait
             CLRF potL                  
             CLRF potH                  
             MOVLW in_pot               ; Get input from pot.
             TRIS 5h
             BCF 5h,d'0'                ; Clear output latch for pot bit.
start_loop   BTFSS 5h,d'0'              ; IF pot = 0 THEN :done
             GOTO start_done
             MOVLW out_pot              ; Discharge cap a little.
             TRIS 5h
             MOVLW in_pot               ; Change pot pin to input.
             TRIS 5h
             INCF potL                  ; Incerement potL.
             BTFSC status,z             ; If zero then potL overfolowed, so
             INCFSZ potH                ; increment potH. If it overflows, exit.
             GOTO start_loop            ; Overflowed? No: loop.
start_done   MOVLW d'2'                 ; Divide 16-bit number represented by
             MOVWF temp
start_div    BCF status,c               ; potH and potL by 2^temp (in this case,
             RRF potH                   ; 2^2 or 4). This scales the pot value to
             RRF potL                   ; fit within an 8-bit range.
             DECFSZ temp                
             GOTO start_div
             MOVF potL,w                ; Show the outcome on LEDs.
             MOVWF 6h
             GOTO start                 ; Do it a
             
             
             end