Modbus TCP server

Available from firmware 2026.0 LTS

From firmware version 2026.0 LTS, the Modbus TCP server function is implemented into the Automation Runtime Platform (ARP) of PLCnext Technology. This Modbus TCP Server can be configured via the PLCnext Engineer programming software. The implementation depends on the libmodbus open source library, provided by libmodbus.org. 

How to configure the Modbus TCP server

• Make sure the Modbus TCP Server service is activated on your controller (System services page in the Web‑based Management). 
• Open the PLCnext Engineer software suite (2026.0 LTS or newer) and start a project from a template of your device.
• Import the PLCnext Engineer Modbus library:
  • In the COMPONENTS panel, right-click on the Libraries section.
  • Right-click the Libraries folder and select Add Library from the  context menu:
    
  • From the PLCnext Engineer directory that opens in the Windows Explorer, pick the Modbus.pcwlx library.
    ↪ The Modbus library is copied into your PLCnext Engineer project.
    ↪ A Modbus node becomes visible in the Network section of the COMPONENTS panel:
    
• To assign the Modbus TCP Server feature to your device, unfold the Modbus → Devices folder stack down to the Modbus TCP Server items: 
  
• Click and drag the appropriate Modbus TCP Server item from the right-side COMPONENTS panel over to the left-side PLANT panel and drop it onto the controller.
  ↪ A Modbus TCP Server node becomes visible:
  
• Double-click the Modbus TCP Server node in the PLANT panel to open the Settings tab in the working area.
  

You can specify in the settings whether data swapping is required, which port should be used by the server, the watchdog and the update cycle time. 

Further information on the setting options for the Modbus TCP server, registers and data lists can be found in the PLCnext Engineer online help in the topic Configuring the Modbus/TCP Local Server