P1.6和P1.7為上下輸出
P2.6和P2.7為上下控制按鈕，按下輸出高電平。
P1.0～P1.3分別是一二三四層的光控點，接通輸出高電平。
電梯到頂按向上無反應，電梯到底按下降無反應。
        org 0000h

main:   clr p1.6
        clr p1.7

        jb p2.6,down
        jb p2.7,up
        jb p1.0,first
        jb p1.1,second
        jb p1.2,third
        jb p1.3,fourth


        sjmp main

first:  mov p2,#01h
        sjmp stop

second: mov p2,#02h
        sjmp stop

third:  mov p2,#03h
        sjmp stop

fourth: mov p2,#04h
        sjmp stop

down:   jb p1.0,first

        clr p1.7
        setb p1.6
        acall del
        jb p1.0,first
        jb p1.1,second
        jb p1.2,third
        jb p1.3,fourth
        sjmp down
up:     jb p1.3,fourth
        clr p1.6
        setb p1.7
        acall del
        jb p1.0,first
        jb p1.1,second
        jb p1.2,third
        jb p1.3,fourth
        sjmp up
stop:   clr p1.6
        clr p1.7
        sjmp main
del:    mov r5,#5
d1:     mov R6,#255
d2:     mov r7,#255
        djnz r7,$
        djnz r6,d2
        djnz r5,d1
        ret
        end