内容： 1、试验目的：了解按键的扫描原理

2、实现现象：同时按键抢答，先按的键有效，其他按键锁死 复位后重新开始抢答

3、硬件要求：按键 LED灯

原理：最先按下按键者有效，其他均无效-Contents: 1, test Objective: To understand the key principles of scanning two to achieve phenomenon: the key to answer in the same time, press the key and effective, other key-lock reset and re-start to answer in 3, the hardware requirements: button LED lights principle: first press the keys are valid, others are null and void