Changing the unit identifier of Modbus TCP devices

Every Modbus TCP device uses a unit identifier (usually set to 255) in the background, which is equivalent to the RTU Modbus client address.

The unit identifier is usually not visible in ABT Site. In some cases, it might be necessary to change the unit identifier for a Modbus TCP device.

info

Only devices from version 1.1 support changing the unit identifier of Modbus TCP devices. Check for updates.
Updating application templates and graphics libraries

Once you have configured the unit identifier of a Modbus TCP device, you can drag the whole Modbus gateway to your Custom library. From the Custom library, you can reuse the Modbus gateway or share it with other users.

 

Change the unit identifier of a Modbus TCP device

  1. There is at least one configured device.
  1. Go to Building > Building structure.
  2. Right-click a device and select Go to engineering.
  3. Open the Modbus task.
  4. Click Add network to add a TCP network. Info: Depending on the used device, up to 5 networks for Modbus, M-bus, KNX PL-Link are supported.
  5. Click Add gateway to add a Modbus gateway.
  6. In the Add gateway dialog box, enter a random IP address for the gateway line.
  7. The Modbus gateway line is for temporary use only. It is not needed later on.
  8. Click OK.
  9. Right-click the gateway line and select Delete.
  10. Right-click the Modbus gateway and select Add device to create a new TCP device or drag and drop a device from the library.
  11. Select the TCP device and open Properties.
  12. Change the unit identifier ("Client" RTU address) to the specific address of the TCP device.