利用二极管的单向导通性，区别两个对称键。扫键思路：对逐个IO口扫键，其他四个IO口可以分别检测其所在的四个按键。-Take advantage of the the single wizard continuity diode, the difference between two symmetric key. Sweep key ideas: IO port one by one sweep key four IO ports can be detected anywhere in the f