Technical FAQs

Ask a Question

Connection lost between the Unity-Pro PC and the PLC just after the Run command through the USB driver

Goals and Symptoms

The Unity-Pro project is transfered through the USB port and the connection is lost just after the Run command.
The animation remains frozen and the following message is displayed :
"PLC failed - Automatic return to off line"

The PLC remains in Run mode, every time you try to connect it again the same message is displayed.

Causes and Fixes

The connection is lost because the project has a long Scan Time and the request takes more time than the driver timeout to get an answer.

You have to change the timeout of the driver, for that :
- Under Unity-Pro, select in the menu PLC -> Set Address,

- In the PLC area, click on the "Communication Parameters" button,

You can increase the Timeout to 10 seconds in order to stay connected.

-Click OK to validate.


Legacy KB System (APS) Data: RESL167997 V2.0, Originally authored by on , Last Edited by on
Related ranges: Unity Pro
Was this helpful?
What can we do to improve the information ?