程序功能：用扫描方式读取四个独立式按键的键值，同时将按键的键值在数码管上显示出来 测试说明：按动K1~k4四个按键，观察数码管显示-Program features: by scanning way read four key values of independent type buttons, at the same time will be the keys of the buttons on the digital tube display Test descr