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 the reference value of the case judgment are modified in the interruption. If it is in trouble, it can be implemented by a macro definition. Some functions can be annotated if they do not work.)