We are building up a new application to replace an older SCADA system. We don't want both systems polling the end devices so VT's port tags are all disabled until we are ready to commission.

However, the modbus devices are still getting polled somehow. We see poll failures where there should be zero activity. When failing over to the backup server, we saw tens of thousands of polls attempted without our intervention or control. On a disabled port.

Has anyone else seen this behaviour? Its a very concerning behaviour and it might consistently crater our 600+ modbus device system. We had been using 12.1.23 and just upgraded to 12.1.27.

Thanks.

Please be sure to also disable any port tags in VTScada also to stop the drivers from polling. This includes any parents to the port tags in use as [*Driver] will find the first parent it can.

Also, please be sure to deploy changes to all servers to ensure they are not simply made to the primary server.

I did a quick test in VTScada using a simple system and wasn't able to see any polling with the port tag disabled. I used VTScada's built in trace viewer app to check for driver traffic while toggling the port. a sample of each is shown below. You can add the trace viewer by adding an existing application in VTScada to check out your own traffic.

All port tags were disabled at the time. Our communication summary page still shows multiple attempted polls over the course of a few days. Even at 230 am when the app was just sitting idle, with all ports disabled, and no one was doing any work on it.

Trihedral Engineers have identified a bit of code that wasn't included in the newer versions of the Modbus driver. It will be corrected in an upcoming version.