io扩展及全双工通信更改后.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 
	MOV DPTR,#0FF2BH
	MOV A,#90H
	MOVX @DPTR,A
	SETB TI
WAIT:	JMP WAIT
RET 
CXZD:	CLR EA
	JB TI,FSJS
	CLR RI
	MOV A,SBUF
	MOV DPTR,#0FF2AH 
	MOVX @DPTR,A
	SETB EA
	RETI
FSJS :CLR TI
	MOV DPTR,#0FF28H
	MOVX  A,@DPTR
	MOV SBUF,A
	SETB EA
	RETI
      
END