The Problem
When connecting to an M580 PLC via USB through a VMware virtual machine, VMware may report a persistent USB connection to the PLC even after the USB cable is physically disconnected. The VM continues to see the PLC as connected, and you can observe connection re-establishment attempts — even after rebooting the VM.
Why This Happens
VMware manages USB devices through a virtualization layer. When a USB device is passed through to the guest OS, VMware creates a virtual USB device entry. If the disconnection is not cleanly handled — which can happen with industrial USB drivers — the virtual device entry persists. The VM keeps trying to re-establish the connection because it believes the device is still attached.
Impact
- Confusing diagnostic information — you may think you are connected to the PLC when you are not.
- Unity Pro / Control Expert may show a connection status that does not reflect reality.
- Potential for data being sent to a phantom device, causing timeouts and errors in the programming software.
Workaround
- Disconnect the USB device from within VMware before physically unplugging. Go to VM > Removable Devices > Schneider USB > Disconnect.
- If the phantom connection persists, go to VM > Removable Devices and manually disconnect the USB controller entry.
- As a last resort, shut down the VM (not just reboot), physically disconnect the USB cable, and then start the VM fresh.
- Check VMware USB controller settings — ensure USB compatibility is set to match your hardware (USB 2.0 vs 3.0).
Recommendation
Where possible, prefer Ethernet connections to the M580 over USB. Ethernet connections are managed by the network stack, which handles connect/disconnect states more reliably in a virtualized environment. USB passthrough in VMware has known quirks with industrial devices.