; USING RB0 INTERRUPT
;
; THIS IS A PROGRAM TO TEST RB0 (EXTERNAL INTERRUPT PIN)
; AT EVERY INTERRUPT ON RB0 OF THE PIC, SUBROUTINE ISR IS EXECUTED
; THE MAIN PROGRAM JUST INCREMENT THE VARIABLES R0, R1, AND R2 IN A
; LOOP EXECUTION.
; THE ISR CLEARS THE VALUE OF THE VARIABLES WHENEVER INTERRUPT OCCURS


        LIST            P=16F84
	ERRORLEVEL      -302
	#INCLUDE P16F84.INC

;************************************************************
; REGISTER DEFINITIONS
;************************************************************
	CBLOCK	0CH		; VARIABLE ALLOCATION.
		R0		
		R1		
		R2		
	ENDC
;************************************************************************
;THIS PART INITIALIZES THE PORTS AND OTHER PHERIPERALS IN MICROCONTROLLER
;************************************************************************
	ORG 	0000H 		; SET POWER ON RESET VECTOR.
	CLRF	PORTA
	CLRF	PORTB
	GOTO INIT
	ORG 	0004H 		; SET INTERRUPT VECTOR.
	GOTO ISR
	ORG	0005H
INIT
	BSF 	STATUS,RP0	; SET BANK = 1.
        BCF	OPTION_REG,7	; ENABLE BUILT-IN PULL-UP RESISTORS.
        BCF	OPTION_REG,6	; SELECT INTERRUPT ON RISING EDGE.
	MOVLW	b'00000000'	; SET PORTA ALL TO OUTPUT.
	MOVWF	TRISA	
       	MOVLW 	b'11111111'	; SET PORTB ALL TO INPUT.
        MOVWF   TRISB	
        BCF 	STATUS,RP0	; SET BANK = 0.
;**************************************************************
; ENABLING THE INTERRUPT AT RB0/INT PIN
;**************************************************************
	BCF	INTCON,1	; SET RB0 INTERRUPT TO DID NOT OCCUR.
	BSF	INTCON,4	; SET RB0/INT AS INTERRUPT.
        BSF	INTCON,GIE	; RB0/INT IS NOW READY FOR INTERRUPT.

MAIN
	INCF	R0
	INCF	R1
	INCF	R2
	GOTO MAIN
;****************************************************************
; THIS ROUTINE EXECUTES EVERY RISING EDGE OF RB0/INT PIN 
;****************************************************************
ISR
	BCF	INTCON,7	; DISABLE GIE SO THAT NO INTERRUPT ALWAYS OCCUR.
	BCF	INTCON,1	; SET RB0 INTERRUPT TO DID NOT OCCUR.
	CLRF	R0		
	CLRF	R1
	CLRF	R2
	RETFIE			; RETFIE RELOADS PC WITH THE SP AND AUTOMATICALLY
				; ENABLE GIE.
	END