Teledyne LeCroy UWBTracer User Manual User Manual
Page 208
Chapter 12: Recording Options
UWBTracer/Trainer User Manual
190
LeCroy Corporation
If you enable capture, select the Channel 0 Speed:
•
Auto-Detect: By default, the Analyzer discovers the speed at which traffic is
running on the device and labels packets accordingly.
•
Low: For use with known Low speed devices, the Analyzer records only at
Low speed.
•
Full: For use with known Full speed devices, the Analyzer records only at Full
speed.
•
High: For use with known High speed devices, the Analyzer records only at
High speed.
Use the default setting Auto-Detect unless you have problems with your recordings.
Rarely, the auto-detection circuitry causes Full Speed devices to fail to enumerate on
plug-in. To solve this problem, change the Analyzer speed to Full speed.
For other recording problems, change the Analyzer speed to Low, Full, or High to debug
the problem. For example, if a device is producing numerous errors at a particular speed,
set the recording to that speed to check that the Analyzer is not misreading the error
packets and labeling them with the wrong speed (this possibility is highly unlikely and is
used here only as an illustration of setting manual speeds).
Manually setting the recording speed guarantees that the Analyzer always records
packets at that speed.
Notes on High Speed Recordings
Erroneous chirp blocks can be recorded on an idle bus when the device has its
FS terminations on while the Host has HS terminations connected. This causes a small
differential voltage ("tiny-J") on the USB bus that causes false chirp detection.
This condition occurs during speed negotiation:
•
On an HS bus, the condition is momentary just before the device chirps.
•
On a CS bus, the condition occurs both before and after the device chirp (until
the end of Reset). Do not use HIGH speed to record signals on a classic
speed bus.
•
The Analyzer stops recording anything for 2.5 milliseconds following an FS_K
state (which is at least 2 microseconds long). Stopping recording avoids
presenting any useless information while the high-speed probe settles down.