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July 1, 2022 - I have a RUT955 can cannot get the MODBUS-RTU Serial polling my PLC. I am just trying to poll for two registers to start with before I add any more. I am not able to get technical support in the USA, so I thought I would try this forum. There is a small LED that is flashing red/green on the back lower right near the LTE signal strength bars. Not sure if that means polling.

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Be advised, that the RUT955 is fully supported by official openwrt. Based on this, Being a freelancer, I developed custom firmware for a large fleet of RUTs to be used as data  concentrators in IoT. Lower level devices are connected via ModBus/RTU, no problem. In your case, you should try to connect a ModBus Simulator, i.e. ModRSsim2, to your RUT, to verify the polling, and electrical setup.
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Thank you for contacting Teltonika networks Crowd support.

From the pdf file shared I can note that you are using an old firmware on RUT955. Kindly update to the latest firmware for this solution is based on RUT9_R_00.07.02.3. To update the firmware, go to

SYSTEM >>FIRMWARE >> UPDATE FIRMWARE you can update from the server (Recommended) or download the firmware from

And update from file.

The following links shows step by step on how to configure Modbus and RS232.

For testing purposes you can use a Modbus Simulator of your choice like ModRsim2.

Kindly follow the above steps, for more technical support, revert.

Kind regards,