This allows for a quicker lock up time when using Machine Control software to queue a video deck with Pro Tools online. However, it does not allow Pro Tools to receive incoming time code back up through the 9-pin cable. It simply allows Pro Tools to receive a quick, one time message from the deck that says its playing, thus allowing Pro Tools to start. The USD is the only device that can send this Digidesign proprietary code to Pro Tools and is thus required. It also requires that both the USD and deck are locked to black burst.