We have been working extensively with Teltonika Support regarding the Modbus TCP communication between our SCADAFlex II PLC and our RUT241 router. All Teltonika‑side configurations have been verified, including:
RUT241 Modbus TCP Client enabled
Correct Server IP (SCADAFlex LAN address), Port 502, and Unit ID
Appropriate function codes selected for the registers we are attempting to read
Proper polling interval and timeout values
Confirmed that no firewall or routing rules are preventing LAN‑side Modbus communication
Our goal is to have the RUT241 read Boolean alarm states from the SCADAFlex controller so that these values can trigger SMS notifications through the router. The SCADAFlex is configured to expose the required registers, and we have validated locally that the SCADAFlex is holding the correct values.
However, despite correct configuration on both devices, we are not receiving any successful Modbus responses to the specific register addresses we are polling. All requests are timing out with no data returned. We have verified that:
The SCADAFlex Modbus TCP Server service is running
The registers we are polling are within the active Modbus map
There are no IP conflicts or subnet issues between the PLC and the RUT241
Physical connectivity and network addressing are correct
At this point, we need Teltonika’s assistance in determining why the RUT241 Modbus TCP client is unable to read registers from the SCADAFlex II device, despite proper addressing, function codes, and network routing.
Any guidance you can provide to help us resolve this issue and complete the Modbus/SMS alarm configuration as soon as possible would be greatly appreciated.
Could you confirm where you contacted us so I’m able to properly assign the right person? Or are you in contact with us via another communication channel?
We have been working with support over the phone a few times, and they advised us to post here to receive additional assistance with this issue. Thank you.
Could you please share screenshots of your exact Modbus TCP Client configuration on the RUT241?
When configuring the register on Teltonika devices, do not use the full prefix (e.g., 40562). Instead, just enter the value 562 . Selecting Function Code 3 (Read Holding Registers) automatically tells the router to look in the 40001-49999 range.
Additionally, please note that RutOS uses Register Numbers (starting from 1), whereas many other devices use Register Addresses (starting from 0). Thus, if that 562 is a register address, then on Teltonika, you will need to specify the number 563.
Thank you again for the helpful feedback earlier. I was able to get the system to begin registering successful Modbus requests; however, I’m still unable to trigger alarms. I’ve attached my current configuration below.
From what I can confirm on my end, the alarm condition is active, the Boolean value is sending a “1,” and my personal phone number is correctly listed as the SMS recipient. Despite that, no alarms are being triggered or sent.
Could you please help me verify the remaining configuration steps to ensure alarms are properly generated and delivered? I appreciate any guidance you can provide.
Could you please send a screenshot showing the value you receive when sending a test request?
Also, try changing the condition to Equal
Additionally, please disable the Test request and leave only the alarm configuration enabled to see if that makes a difference, since the request is not required for the alarms to function.
I completed the update and set the value to 0 to test whether the alarms would trigger. The interface shows that alarms are being triggered; however, I am still not receiving any SMS notifications. Do you know why the alarm may be triggering without sending any text messages to the phone number I entered? I did enable the requests configuration again because it didn’t seem to make a difference. The biggest difference was made by changing the value to 0 for the alarm. Please help me enable the texting when an alarm is triggered!
Per your request, I have attached the screenshots for reference. Thank you!
Could you please try sending SMS messages directly through the WebUI, without using the alarms, to confirm whether that works first? You can do this by navigating to Services → Mobile Utilities → Messages.
When entering the phone number, please include + or 00 before the number. If you are in the USA, you may need to add a single 0 before the number, if I remember correctly.
Thank you very much for the suggestions. I’ve tried all of the configurations you recommended, but unfortunately the issue is still occurring. If you have any additional ideas or troubleshooting steps I could try, I would greatly appreciate it. Thank you again for your help!
Do you happen to have any other recommendations? I am not sure why it will not text my phone only from the alarms. I was able to send SMS messages to myself through WebUI. Thank you.
For troubleshooting purposes, we will require more sensitive information from your end, such as the troubleshoot file, which may contain passwords, public IP addresses, serial numbers, and such. To avoid leaking this information, we have sent you a form to fill out, which you will receive in your e-mail inbox that you have registered your account with in the forums. In the Ticket ID field of the form, please enter the ID of this thread, which is 17934.
