PC机通过串口向单片机发送命令，单片机驱动步进电机工作在正转、反转、正转n圈后反转，反转n圈后再正转，启动、停止、转速设置等功能-PC through the serial port to send commands to the microcontroller, the microcontroller to drive a stepper motor in forward, reverse, forward n laps after reversal, reverse and then for