MOV	TMOD,#10H		
		MOV	R3,#200		
AGAIN:	MOV	TL1,#08H		
		MOV	TH1,#01H		
		SETB	TR1			
BACK:		JNB	TF1,BACK		
		CLR	TR1			
		CLR	TF1			
		DJNZ	R3,AGAIN