pic18f4520单片机键盘中断扫描 有定时器产生200ms扫描4x4键盘一次（注意：单片机定义输入端口要加上拉电阻）-pic18f4520 microcontroller scans the keyboard interrupt timer generates a 200ms scan 4x4 keyboard (note: the microcontroller input port to define the pull-up resistor)