Teledyne LeCroy QPHY-USB - Manual (Page 53)

QPHY-USB Software Option
QPHY-USB Operator’s Manual Rev F
53
Host Low-Speed Downstream Signal Quality
1. Set up the equipment as shown in the following figure.
2. Select Host in the Mode control and LS Downstream Signal Quality in the Test control of the USB Test
Wizard.
3. Use the SQ Device section of the Test Fixture as the SQiDD in the following figure. Ensure the TEST/INIT
switch is in the INIT position. The best method to capture and analyze Low-Speed downstream signal
quality is to capture both a keep-alive (Low-Speed EOP) and a packet. The root hub is required to either
generate a keep-alive or send Low-Speed traffic once per frame whenever a Low-Speed device is directly
attached. Capture downstream traffic with Low-Speed devices with a trigger on the rising edge of D-.
Figure 55. Host Low-Speed Downstream Signal Quality Test Equipment Setup
Note: The USB-IF High-Speed Electrical Test Tool is not used for this test and should not be running.
4. Press the Single Acquisition button on the oscilloscope until a full packet is displayed on the screen. The
full packet may consist of the keep alive and a data packet, or could be just a data packet and should fill
most of the oscilloscope screen. Use the cursors to select the downstream portion of the data packet
(shown as follows). The cursors are set to 1 UI before the first bit in the sync field on the left and 1 UI after
the end of the EOP on the right.