MOV	A,#80H	
		MOV	R1,#CRPORT	
		MOVX	@R1,A		
BACK:		MOV	R1,#CPORT 	
		MOVX A,@R1		
		ANL	A,#00000001B	
		JNZ	BACK		
		
		MOV	R1,#APORT 	
		MOVX A,@R1