RUT956: MODBUS TCP over Serial Gateway not working

Networking Solutions Issue
1

We have been using MODBUS TCP over Serial Gateway on loads of RUT956 and it has stopped working since firmware version > RUT9M_R_00.07.13.4

To reproduce this problem, please follow these steps:

  • use a RUT956 with firmware version RUT9M_R_00.07.13.4
  • configure MODBUS TCP over Serial Gateway: timeout=1 s, Device=rs232, “9600,n,8,1”, Server ID configuration=”User defined”, Server ID=1
  • connect a MODBUS device with server ID=1
  • use QModMaster to read Holding Registers (0x03) from IP=192.168.1.1, Start Address=1, Number of Registers=2, Unit ID=1 –> it works
  • repeat the previous step using Unit ID=2 (same MODBUS device with server ID=1) –> it works

Now, update the firmware version to the late current version RUT9M_R_00.07.20.3_WEBUI.bin and repeat the previous steps:

  • QModMaster, Read Holding Registers (0x03) from IP=192.168.1.1, Start Address=1, Number of Registers=2, Unit ID=1 –> it works
  • QModMaster, Read Holding Registers (0x03) from IP=192.168.1.1, Start Address=1, Number of Registers=2, Unit ID=2 (same MODBUS device with server ID=1) –> it doesn’t work

Please, follow these steps and let me know if the result is the same.

Thanks in advance.

3

Hello,

I reported the error you experienced to Teltonika back in July 2025. The User defiied ID parameter does not work! We experienced this with the TRB142, TRB145 devices. Unfortunately, the error has not been fixed since then!!!

Best regards

4

Greetings,

Thank you for outlining the issues you’re experiencing. I will test this configuration and get back to you with the results as soon as possible.

Best Regards,
Justinas