When using a USD the serial time code goes directly into Pro Tools via a serial port, not the USD. Pro Tools is not designed to echo the time code back out to the USD for display on it's front panel. The inherent latency limitations makes doing this prohibitive.On the SYNC I/O serial time code is passed directly to the CPU without being "intercepted" for display on it's front panel. It is conceivable that this may change in a future release.