Question

Hi,

We have a RUTX11 setup as a ModBus slave. As a test it works but has lots of timeout issues. We are only requesting 6 registers for now.

From the master, we have tried timeout from 1s to 5s. Polling window from 500ms to 2000ms.

On the slave "keep persistent connection" and connection time from 0 to 30s.

No matter the setting, we are getting timeout issues. The system eventually recovers but then timesout as short time later. This is not a workable long term solution.

Is there somewhere I can look at the modbus slave process and see why it's not responding in time? Is there a log?

Thank you, Chris.

Answer 1

Hello,

Currently, MODBUS does not provide any logs or debugging tools.

Keep persistent connection option should stabilize the connectivity. If it does not help, could you check if you have stable internet connectivity on your side.

Also, you could send a number of ping requests to check if there are any losses or significant deviations of round trip time between the slave and master devices.

Also, which firmware version is the router running on? 

Best regards, 

Comments

Hi,

We are running firmware RUTX_R_00.07.02.7.

To simplify the test, we are running with no WAN connection, just 1x local LAN to PC.

I've had ping -t running while using modpoll to request the first 6 holding registers. See attached screenshot.

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Just another thing worth noting...

I've run the same setup with a TRB140 on TRB1_R_00.07.02.3 and its working fine, via LAN but with an active 4G WAN connection.

So I've moved the SIM card across to the RUTX11 and the problem goes away, modbus works fine.

Which brings me to another interesting issue, when polling the following registers without active Sim WAN it get errors. Register numbers 24 and 120.

Maybe there is a blocking call between the modbus program and the modem drivers?

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The data in registers with numbers 2, 3, 4, 5 are taken from the modem and since the modem is not connected to the operator at the time of testing, some miscommunication between CPU and modem might interfere from accessing the data.

Data in register 24 contains mobile operator's name, while register 120 contains mobile data connection type. Since without SIM card no connectivity to any operator or network is established, data is unavailable and results in errors.

You can find information about all data accessible with MODBUS and registers associated with it in RUTX11 here.