User Manual

Fig. 8: Adding a new license
What to measure
With USB analyzer plugin users can analyze USB 1,5 Mbps (Low-Speed) and
12 Mbps (full speed) data rate communication captured by SIGMA2 analyzer.
Measure tool attachment
Although USB data comunication si partly differential, GND and both USB data
signal (DATA+,DATA-) must be connected to SIGMA2 analyzer. SIGMA2
samples that signal with enough accuracy as a common TTL signal. Due to
NRZI coding, which USB uses, analyzer does not distinguish between
DATA+,DATA-, so they are interchangeable. But there are some line states on
USB using single-ended signalling (e.g. Bus Reset a End-Of-Packet); that is the
reason why connecting DATA+, DATA- only is not enough. Swapping the data
lines the data rate is choosen. Behind the USB hub to Low-Speed (1.5 Mbps)
device there is only Low-Speed communication, whereas to Full-Speed
(12 Mpbs) device there are both Low-Speed and Full-Speed communication.
480 Mbps communication is called High-Speed and SIGMA2 is not able to
measure that.
USBprobe, which is attached, includes two 74AHCT125 TTL gates and USB
connectors A and B wired so that it provides a USB extension. SIGMA2 logic
analyzer can be connected before or beyond the logic gates, it depends on an
application – better to try. Generally, better results is reached with USBprobe
connected directly to USB hub and the shorter USB cable, the better. Likewise
it is important to shorten the way between USBprobe and SIGMA2.
On USBprobe there is 5V from PC directly accessible (through a 800mA
irreversible fuse) – avoid a shortage! It is highly inadvisable to join
USBprobe directly to PC ports. We suggest using USB hub with an external
power source and joining USBprobe directly into that.
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