MOV	TMOD,#2H		
						
		MOV	TH0,#0		
AGAIN:	MOV	R5,#250		
		ACALL DELAY
		CPL	P1.0			
		SJMP	AGAIN			
DELAY:	SETB	TR0			
BACK:		JNB	TF0,BACK		
		CLR	TR0			
		CLR	TF0			
		DJNZ	R5,DELAY
		RET