The M-2000 series is a family of network data acquisition and control modules with digital or analog I/O functions. The modules can be remotely controlled through an RS-485 serial bus by using DCON and Modbus RTU/ASCII protocols. The selectable transmission speed of the RS-485 port is up to 115,200 bps. Modbus has facto standard communications protocol in industry, and is now the most commonly available means of connecting industrial electronic devices. The M-2000 series is slim-type Form Factor I/O that provides the saving space for the installation, easy wiring and distributed I/O points applications. The bias resistor and terminal resistor by switch selectable that is used to improve the communication and solve the communication fail of RS-485 network.