2、独立按键

代码说明：

说明：  基于51单片机的按键例程，常见问题： 1. 按键无反应 请您确认程序是否下载成功，连线正确无误，确认无误后还是无效果的话，将排线重新插拔下，单片机拿下来重新安装，重启开发板试试！(Key routines based on 51 single chip microcomputer,common problems: 1. Press the key and no response. Please confirm whether the program was downloaded successfully and the connection is correct. If it is still ineffective after confirmation, plug and unplug the cable again, take down the MCU and reinstall it. Restart the development board to try!)