只需一条线，理论上可接16个按键，但实际不行，按键上要加一个104的电容，保证稳定。参考电压和案件判断参考值在中断中修改，若觉得麻烦，可以通过宏定义实现。有些函数没作用可以注释掉。(Only one line, in theory can be connected with 16 keys, but not in practice, the key to add a 104 capacitance, to ensure stability. The reference voltage and t