ASSUME CS:CODE
START:
MOV AL,10010000B ;控制字表示A、B口都為方式0，A口輸入，B口輸出
MOV DX,203H
OUT DX,AL
S0:
MOV DX,200H ;讀開關狀態
IN AL,DX
TEST AL,01H ;測試PA0
JZ CLOSE ;合上則全亮
MOV AL,00H ;打開全滅，低電平滅，高電平亮
JMP OUTPUT
CLOSE:
MOV AL,0FFH
OUTPUT:
MOV DX,201
OUT DX,AL
JMP S0 ;重復檢測
CODE ENDS
END START