;**************************************************************************
;
;TITLE   PWM on AN2 controled by AD on channel AN1 and displayed on RB0-7
;This program is a simple implementation of the PIC16C71's A/D
;
;	  The A/D is configured as follows:
;       Vref = +5V internal.
;       A/D Osc. =  internal RC
;     
;

;**************************************************************************

#include 	"p16c711.inc"
        	LIST P=16C711

        __CONFIG _XT_OSC & _PWRTE_OFF & _WDT_OFF & _BODEN_OFF & _CP_OFF

;--------------------------------------------------------------------------
; Variables
;--------------------------------------------------------------------------

RAM		  EQU	      0x0C
TEMP    	  EQU    	RAM+0
RESULT	  EQU	      RAM+1
COUNT1	  EQU	      RAM+2
COUNT2	  EQU	      RAM+3
COUNT3	  EQU	      RAM+4

;--------------------------------------------------------------------------
; Program Code
;--------------------------------------------------------------------------

              ORG       0x00       
              GOTO      Start
;
;--------------------------------------------------------------------------
; Main Program
;--------------------------------------------------------------------------

              ORG       0x10
Start
	  	  MOVLW   	B'00000000'     	;set port b as outputs
        	  BSF     	STATUS, RP0     
        	  MOVWF   	TRISB           
        	  BCF     	STATUS, RP0    	
  		  CALL    	INITAD
  
update	  CALL	GETAD      
		  MOVF	ADRES,W         	;get a/d value
		  MOVWF	RESULT
		  MOVWF	PORTB
	
		  BSF		PORTB,0		;turn pin on
		  CLRF	COUNT1

LOOP1		  MOVF	COUNT1,W
		  SUBWF	RESULT,W
		  BTFSS	STATUS,C		;if less than then skip
		  BCF		PORTB,0		;turn pin off
 
		  CLRF	COUNT2
LOOP2		  INCFSZ	COUNT2,F
		  GOTO 	LOOP2

		  INCFSZ	COUNT1,F
		  GOTO	LOOP1
		  GOTO	update

;
; This routine gets the result of an A->D convestion from AN1
; Result is available in ADRES;
;

GETAD		  MOVLW	D'03'		    ;setup time >= 10uS.
		  MOVWF	TEMP
SDLOOP	  DECFSZ  	TEMP, F
		  GOTO    	SDLOOP
    
		  BCF     	ADCON0,ADIF     ;clear int flag
		  BSF     	ADCON0,GO       ;start new conversion
GETADLOOP
		  BTFSC   	ADCON0,NOT_DONE ;a/d done?
		  GOTO	GETADLOOP       ;no then keep checking
		  RETURN	                ;yes then update new value.
;
;
;InitializeAD, initializes and sets up the A/D hardware.
;

INITAD	  BSF     	STATUS,RP0      ;Configure AN1 & AN0 as input
		  MOVLW   	B'00000010'     ;Vref as Reference
		  MOVWF   	ADCON1          ;
		  BCF     	STATUS,RP0      ;
		  MOVLW   	B'11000001'     ;RC, AN0, A/D
		  MOVWF   	ADCON0          ;
		  RETURN


		  END