the SL485 serial port expansion board is specially designed for our company's control board to expand the serial port. Usually it can only be used with our company's control board. through the serial port expansion board, one 485 serial port can be expanded into two 485 serial ports, which can be realized: 1 serial port the board can be connected to two handheld programmers or monitor and handheld at the same time. It can be expanded to monitor and so on in the dual serial port board with internal and external computers or modular computers, which is flexible and convenient to use.