Modbus
      Back to home
      1. GI.knowledgebase
      2. Connectivity & Integration
      3. Modbus

      Configuring the Controller as a Modbus Slave

      Steps to set up a controller as a Modbus TCP/IP or Modbus RTU slave (server) for reading and writing data.

      To set up the controller as a Modbus RTU slave, a USB-to-RS485 adapter or a Modbus TCP-to-RTU gateway is required. Please refer to this page for a list of compatible devices.

      Due to the limitation of having only one data port available, running Modbus TCP/IP concurrently with ASCII TCP/IP is not feasible.


      1. Start GI.bench and open an existing project or load your online controller configuration.

      2. Double-click on the controller to open the Controller Settings.

        1. To set up Modbus TCP/IP, navigate to the Dataport section. Change the protocol to either Modbus TCPIP Class 0 or Modbus TCPIP Class 0 (word swapped). The default port for Modbus TCP/IP is 10000.

        2. To set up Modbus RTU go to the USB Devices settings and change the Device count to 1. Select the USB port and change the Type to ModbusRTU slave. Enter the corresponding Address and Baudrate.

      3. It is enabled by default, but to check or change protocol permissions, right-click the controller and select Edit > Edit Data Access Rights.

      4. Ensure that the desired channels are selected for READ or WRITE permission.

      5. Write the updated configuration to the controller.

      6. In the toolbar, select Export > Export Variable Info to save the variable information in a CSV file.

      7. Open the CSV file to view the Modbus register for each configured variable. The register offset for the first channel is 999 (hex 0x3E7).

      8. Use the Q.station's IP address, port number, and channel registers to read signals with a Modbus master.