Begin the test procedure with all necessary devices disconnected and powered down. Ensure the VID/PID device is set to the desired test type. For high-speed signal quality testing, a PID of 0x0104 is desired (TEST_PACKET).

1. Power relay board and set it to the "init" position
2. Connect the "test" port of the relay board to the TUSB21XX's input
3. Connect oscilloscope to relay board
4. Connect head unit/embedded host to the TUSB21XX's output and power it on
5. Toggle RSTN (reset) on TUSB21XX
6. Connect VID/PID test host device to the "init" port of the relay board
7. Set relay board to "test" position

As with all prior modes of testing, both CD and ENA_HS are low initially. Upon connection of the VID/PID test host device (Step 6), the CD flag switches high (Figure 4-2). Shortly following this, after successful enumeration by the embedded host, ENA_HS also switches high (Figure 4-3). If this does not occur, ensure that the VID/PID device is active and presenting the correct VID/PID combination. For some system setups, the embedded host must be powered on prior to the VID/PID device to properly enumerate it. Also ensure the relay board is set to the "init" position to support handshaking.

After enumeration has completed, the embedded host immediately begins sending test packets. Once the relay is set to the "test" position (Step 7), test packets will appear on the oscilloscope input (Figure 4-4).

The test packets will continue to be sent by the embedded host until it is powered off. ENA_HS switches low after the relay board is switched back to the "init" position (Figure 4-5).

Finally, after disconnecting the VID/PID device, CD switches low (Figure 4-6).