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USB 2.0 HS


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Asking if this Logic Analyzer, which is specified as 800 Mbps can capture USB HS 480 Mbps digital signals.  For USB FS (12 Mbps) I use a 50 Mbps Logic Analyzer, capture the traffic, then run the binary file through protocol analyzer software. The question, again, is if this device can capture 480 Mbps data on two signal lines (D+ and D-). Thanks

 

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@RomanB,

I haven't used this instrument but I read through the literature. I'm doubtful that you can use for capturing traffic on the DP and DM lines for a number of reasons. The most important ones are that the Digital Discovery isn't meant for differential signalling. A bigger hurdle is that USB 2.0 uses the UTMI signalling standard that is quite complex; there is no Xilinx IOSTANDARD that I know of that is compatible with UTMI. A bigger problem is that asynchronous sampling of a 480 MHz signal with Fs = 800 MHz doesn't quite do the job. Could someone make an adapter for doing this? I'm not sure. I'm reasonably certain that direct probing of an active DP/DM lines would be problematic. But as I mentioned there are companies that do provide USB bus analyzers, some at reasonable prices, though not for what Digilent charges for the Digital Discovery. In general you can't replace very expensive things with very cheap things and be happy with the results. There are exceptions, for a limited set of use cases, where you might be able to break the rule.

Perhaps someone at Digilent will take the time to look into your question but I'll be surprised if you get the answer that you want.

Edited by zygot
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Some interesting information:

The datasheet for the Digilent Digital Discovery lists the FPGA device as a XC6LX25-2C5G324, a -2 speed device.

According to the Switching Specifications for this device:

  • Fmax for BUFH is 375 MHz
  • Fmax for BUFIO2 is 500 MHz
  • The maximum PLL output frequency is 950 MHz

The maximum LVDS ISERDES2 (retimed mode) data rate is 750 MHz.

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