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DSOX4USBSQ USB 2.0 Signal Quality Analysis Application Electrical Testing Notes
5
Hub Downstream Signal Quality Testing
You can run tests when the oscilloscope is already stopped. This is
useful in the case of embedded hosts (and other cases) where the
device under test (DUT) may not easily be placed in a test mode, and
you want to analyze already acquired data.
See Also
•
Chapter 6
, “Saving Test Results to an HTML File,” starting on page 81
Hub Downstream Low Speed Connection
Perform these connection steps:
1
Use the passive probes included with the oscilloscope.
2
Attach the passive probes to the oscilloscope's Channel 3 and Channel 2
inputs.
3
Attach the SQiDD board to the hub under test.
4
Attach the upstream port of the hub under test to the end of 4
self- powered hubs and a host system. Hub #1 has to be a full speed
hub. The other hubs can be either full speed or hi- speed hubs.
5
Attach a low speed device to the same section of the SQiDD board. If
the section has a switch, it should be set to ON.
6
Connect the oscilloscope Channel 2 probe to D+ probe point of the
device under test portion. Connect the oscilloscope Channel 3 probe to
the D- probe point of the device under test portion.
7
Exit the HS Electrical Test Tool if you have previously launched it.
N O T E
The best method to capture and analyze low-speed downstream signal quality is to capture
both a keep-alive (low speed EOP) if present and a SOF packet. Hubs are required to
generate keep-alives when there is full speed traffic and pass them on to low speed
devices.
