Hi all

For a project I'm trying to communicate from a Logo to a concens icon actuator over Modbus RTU. Therefore I have a CIM that acts as a Modbus RTU master.

I have been able to communicate from my pc to the actuator using the software Modbus Poll. Also, I was able to communicate from my pc to the CIM using the software Modbus Slave. Unfortunately, the communication straight from the CIM to the actuator has issues.

This is my test setup on the CIM

From this pdf on page 18, we see that register 1000 and 1001 should represent the uptime of the actuator. To test the communication, I'm trying to readout this value. I'm writing this value to VW0:

From there I'm using the online monitor to check this VW0:

As you can see, I can get a value. This value does look right, but unfortunately this updates very very slowly (more than a couple of minutes between updates) and inconsistently.

Wiring

From the CIM I've connected a twisted pair from port A and B, to port A+ and B- on the actuator. I've also connected both signal grounds together. This cable is only 0.5 m long. I've also enabled the terminal resistor on the CIM. On the actuator side, I haven't added a terminal resistor, as apparently this isn't necessary for small setups like this.

Does anyone know why this could be so unstable or how to troubleshoot this any further?

Thanks in advance! 

Maybe the communication is too fast with default values for the equipment and only manages to pass once in a while. Try to extend the “modbus response delay” of the slave (some register according to manual) and also set the CIM's customized interval to something longer, like 200ms.

Thank you for the quick response.

I updated the custom interval in the cim to 200 ms, and the read delay on the actuator to 50000 us. Which, according to the manual should total the delay on 53 ms.

Unfortunately this didn't resolve the issue yet.