io扩展全双工通信pa出pc收更改前.txt

51芯片的82C55IO扩展

;PA口发送
;PC口接受
	ORG 0000H
	 JMP MAIN
	ORG 0023H
	JMP CXZD
MAIN:	MOV SCON,#90H
	MOV IE,#90H
NEXT:	MOV DPTR,#0FF28H
	MOVX  A,@DPTR
	JMP $ 
RET 
CXZD:
	CLR EA
	JB TI,FSJS
	CLR RI
	MOV A,SBUF
	MOV DPTR,#0FF2AH
	MOVX A,@DPTR
FSJS :CLR TI
	SETB EA
	JMP NEXT
      
END