1, using serial port switching module: the serial port signal of single chip microcomputer can be converted into signals of other communication protocols, such as RS485 and RS232, so as to realize the function of serial port expansion.

2. Use serial port expansion chips: You can use serial port expansion chips, such as MAX232 and MAX485, to convert the serial signal of single chip microcomputer into multiple serial port signals, thus realizing the function of serial port expansion.

3. Using GPIO port to simulate serial port: The function of serial port can be simulated by using GPIO port of single chip microcomputer, and the communication of serial port can be realized by software, so as to realize the function of serial port expansion. This method needs to realize the related functions of serial port protocol at the software level, which is relatively complicated.