Modbus RTU with PFC100 750-8112 (Codesys 3.5)

CODESYS
1

Hello everyone, I’m new here :raised_hand: and I’m coming straight to a problem for which I currently have no further approach (I’m a bit lost) and I’m hoping for your support and/or experience :flexed_biceps:

I have already read some posts about Modbus RTU here… ultimately without success :face_with_raised_eyebrow: This is my first connection of a Wago PFC to Modbus RTU and also the most tedious one.

  • Controller PFC100 (750-8112) FW04.06.01 (28), CodeSys 3.5 SP19
  • Modbus RTU on local Sub-D, Mode Serial Interface (in PFC to RS485)
  • Connector on SUB-D Wago 750-960, termination resistor switched on
  • In the HW Config, only one Modbus slave was created (see screenshot)
  • Slave Addr.3 (three registers (channels) created)

When the controller is loaded and started, a bus error is displayed for Modbus (time out - no response).

The Modbus slave (eletechsup NT18B07) can be addressed, configured, and the register values can be read via ComTest Modbus (on a notebook). Connection via USB-RS485 adapter.

I assume that since no communication is established, there must be some kind of configuration or hardware error?

No application has been created yet (no FBs available to read the registers); I think it’s pointless as long as communication is not established?

What has already been tried…

  • Different CodeSys version (3.5 SP19)
  • Swapped lines A and B
  • Tested directly on Pin 3 and Pin 8 in the socket
  • Termination resistor at sensor 120 Ohm
  • Shielded (longer) cable

Here is a screenshot of the ModbusDevice Addr.3…

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Here is the configuration and error…

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I hope you still have an approach for me on what I can test/change that will lead to success. If further information is missing or would be helpful, please let me know briefly - I will provide it immediately. (If more productive, feel free to do the whole thing in English)

Thank you very much in advance for your help

2

Hello

The integrated serial port into the controller has a dual electrical interface RS232/RS485 and by default it assigned to RS232. You need to confirm first the port is using the right interface RS485. This have to be done manually thought the WBM (web configuration pages) under the “Configuration” tab go to menu: “Administration | Serian Interface | Assign Mode of serial interface“, select “RS485”, submit and reboot the controller (not sure if the later is required)

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3

Hello Alfonso, first of all, thank you for your response :+1:

I had already set the COM in the PFC to RS485…

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Unfortunately, in the online monitor, the bus connection keeps switching to “Not running.” Next, I will obtain and test another Modbus device.

Best regards, Mattes

4

Welcome!

-Did you check the ‘auto-restart communication’ on the client settings? It’s a good idea for easy startup.

If it still doesn’t work could add a few screenshots of your modbus settings.

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5

Hello MAD2026,

Perhaps this helps:

CodeSys has renamed the Master and Slave.

These are now called Master => Client and Slave => Server.

You can also see this in the last screenshot from Wago above.

Best regards