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by anonymous

Hello All,

I'm working with 2 Teltonika RU955 routers and I'm experiencing the same issue with both.

On both routers I have:
1. Updated the firmware to vRUT9_R_00.07.02.6

2. installed the Modbus Serial Master package

3. Enabled Modbus TCP Slave and verified that I can query the Teltonika's own modbus data using modbus-cli as outlined here: This works correctly

Next I have:
1. Connected a Janitza UMG96RM power analyzer to each Teltonika router as described by the wiring diagram here:

2. I have set up Modbus Serial Master following the directions from Teltonika here: and matching the values specified by janitza here:

3. I have added a slave device and request following the guidance of the previous linked documents

4. Finally I have tested the request via the WebUI and command line, and receive the same error:
"No response from slave device, check wiring and configuration ". The error remains despite changing the baud rate, register, and slave device to all possible options.

Steps taken to troubleshoot:
1. Wiring was replaced completely
2. A 120 resistor was added to the lines
3. Wires swapped to test for reversed polarity
4. Disconnected the RU955 and replaced with usb modbus master device was attached to the same cables. This device was able communicate with the modbus slaves successfully.
5. Re-attached teltonicas to cables and performed a factory reset, repeated the setup steps above and arrived in the same situation. Neither router can communicate with a Modbus Slave over RS485.
6. Switched from using Modbus Serial to Modbus TCP by disabling the Modbus Sewrial Master and enabling RS485 Modbus Gateway. When slave devices are configured this way, I receive the error "unexpected response length"

Any help is appreciated, cheers!

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by anonymous

Can you please share the troubleshoot file using the private message?