The necessary drivers are contained in the MotorolaDeviceManager. Simply run it.
Set Phone to USB Diag Mode
- Power phone off
- Hold volume down while powering on. You see the following menu
- Press volume down until "BP Tools" is highlited
- Press volume up to select
The phone reboots into Android. Now connect the phone to the PC and check the Windows Device Manager for unknown devices. It should look like this:
The port number (COM3) will be used in the QPST tool.
In case the "Motorola QC Diag Interface" shows a yellow warning symbol, please check this article from XDA.
After changing the motport.inf choose to manually update the driver with files on the computer and choose the folder where motport.inf resides. You may get a warning that the publisher of the driver could not be verified. This happens because you modified the inf file, so simply choose to install the driver.