8255_1.asm

我学单片机89C51时编的大部分程序都在里面

        ORG 0000H
        AJMP START
        ORG 0030H
START:  MOV DPTR,#7FFFH
        MOV A,#90H
        MOVX @DPTR,A
CLEAR:  MOV DPTR,#7FFDH
        MOV A,#0FFH
        MOVX @DPTR,A
        MOV DPTR,#7FFEH
        MOV A,#01H
        MOVX @DPTR,A
MAIN:   MOV DPTR,#7FFCH
        MOVX A,@DPTR
        ANL A,#01H
        JZ NEXT
        MOV DPTR,#7FFDH
        MOV A,#00H
        MOVX @DPTR,A
        MOV DPTR,#7FFEH
        MOV A,#00H
        MOVX @DPTR,A
        LJMP MAIN
NEXT:LJMP CLEAR
     SJMP  $