MOV	A,PCON	
	SETB	ACC.7		
	MOV	PCON,A	
				
	MOV	TMOD,#20H	
	MOV	TH1,-3	
		 		
	MOV	SCON,#50H	
	SETB	TR1		
	MOV	A,#"B"	
A_1:	CLR	TI		
	MOV	SBUF,A	
H_1:	JNB	TI H_1	
	SJMP	A_1