Serial port is an extended interface using serial communication. Serial interface is called serial port for short, also called serial communication interface or serial communication interface, which is an extended interface adopting serial communication mode. Serial interface refers to the sequential transmission of data bit by bit. Its characteristic is that the communication line is simple, and two-way communication can be realized only by a pair of transmission lines, which greatly reduces the cost. Especially suitable for long-distance communication, but the transmission speed is slow. Commonly used serial ports are 9-pin serial port and 25-pin serial port. When the communication distance is close (