FAQs from Rohde & Schwarz

USB TMC Connection with HMO3000 fails

Question

When I change the interface settings to USB TMC, the device is stated as “Unknown USB Device (Device Descriptor Request Failed)”

In the device manager I can see a COM interface, which should not happen if "TMC" is set.

On my PC I have installed VISA and the drivers for the HO732 interface board.

What goes wrong?

Answer

This is a typical problem with windows.

If the drivers for the HO732 are installed and a VCP connection has been established before, windows seems to store that and try to use the same driver for a TMC connection.

But that is the wrong driver and the connection fails.


The following procedure solves the problem:


At first please check if the path

C:\Program Files\IVI Foundation\VISA\IVI USB Staging

is existing on the PC. That is the correct driver for a TMC connection.


On the HMO3000 select USB TMC and connect it to the PC

Open the device manager on your PC.

As soon the HMO3000 is connected, a COM port with an exclamation mark is shown as interface

Do a right click on that COM port and select "uninstall" - very important: set the tick mark to remove the driver software!


Usually now the correct driver is installed automatically.

If the driver is not found, direct the installer to the path:

C:\Program Files\IVI Foundation\VISA\IVI USB Staging