4*4点阵键盘的实现。用运反转扫描法来实现对键盘的扫描，确定是那个按键接通，并通过串口输出，显示在显示器上。-4* 4 matrix keyboard implementation. Scanning method used to achieve the reverse operation to the keyboard scan to determine that the button is switched on, and through the serial output, displayed on the monitor.