MYREG	EQU	0x20		
DELRG	EQU 0x80		
	ORG	0000H
	GOTO	MAIN		
	ORG	0008H			
	BTFSS INTCON,RBIF	
	RETFIE			
	GOTO  PB_ISR		
	ORG	00100H	
MAIN	BCF  TRISC,7	
	BSF	TRISB,4	
	BSF INTCON,RBIE	
	BSF INTCON,GIE	
OVER	BRA OVER		
PB_ISR
	ORG 200H
	MOVF  PORTB,W		
	MOVLW D'250'		
	MOVWF MYREG
BUZZ	BTG PORTC,7		
	MOVLW D'255'		
	MOVWF DELRG
DELAY	DECF DELRG,F
	BNZ DELAY			
	DECF MYREG,F
	BNZ BUZZ
	BCF INTCON,RBIF 
	RETFIE
	END