MODBUS IO server serial: No Known Values of Shared Variables, but upadaing ON

[MStewart]

There is a known bug in the LabVIEW DSC that I learned about by opening a service request for a similar problem.  Try opening the advanced properties of the I/O server and changing the Holding registers value to 1.

Spoiler

[Eshk]

Thank You MStewart for a hint, but still no luck. Only possible value about Holding Registers in "advanced properties" are maximum numbers of data points per command. I've tried what you proposed but nothing happens. I have also recorded an video what DSM sees when MODBUS slave device is first disconnected and what happens when we connect it again.

[MStewart · Accepted solution]

It looks like LabVIEW is fighting another process for access to the COM port.  Do you still get the repeated CommFail if you switch to another port?

If you duplicate the steps in this video, can you successfully communicate with the simulator?

*note in the video that sometimes the values in NI DSM do not update until i right-click on the I/O server tree.  I think this is just a bug with the DSM UI.

[Eshk]

Thank you MStewart. I am very grateful for your effort of making the video. It really helped me in solving the issue.

I've duplicated the steps with another port and successfully set the communication with the simulator.

My mistake was incorrect address:i.e. 4000769 instead of 400769.

Also refresh rate was to low ( IO server was set to have refresh rate of 0.5s instead of 1s)

CommFail was also appearing when changing com port  or restarting applications individually.

You were right about com port 11. I uploaded another video where I've tested everything with port 11 and then with port 14. At the end, I've changed the refresh rate to 0.5s

[MStewart]

Glad you were able to get it working.  I know how frustrating it can be to resolve communication issues, especially when establishing COMs to a new device.

On the topic of refresh rate, I have found that the refresh rate in the I/O server properties is not reliable and that the SVE often takes longer than desired to update the values of bound variables.  The workaround that I use is to create a bound variable for UpdateNow and toggle the value, to programmatically enforce my desired refresh rate.