凌阳单片机4*4键盘扩展源代码及原理电路（PDF格式），包括键盘扫描初始化，键盘扫描服务函数，以及键盘防抖动处理程序。-Sunplus Single-chip 4* 4 keyboard to expand the source code and the principle of the circuit (PDF format), including the keyboard scan initialization, keyboard scanning service function, as