Re: cheap USB analyzer based on FPGA

How about using some resistors to reduce the swing, then use a
differential input of the FPGA ?


Jerome wrote:
I checked with a scope after having insterted "spy pins" in the middle of a
AF/AM cable
--> swing is indeed 0v - 3.6V ."spyied" device was a Webcam, used SW was
ampcap.

My scope is old and unaccurate , i'm not sure of the exact acceptable level
for NON 5V tolerant devices
(3.3V? 3.6V?...)

When using live video, there are data frame of length ~40 ms & period ~50 ms
When "zooming", i can see the USB full speed frames every 1 ms.
Theses frames have a duration of ~200 - 250 us when live video is enabled

When no video is enabled, the 1ms frame are still threre but no data


"mk" <kal*@dspia.*comdelete> wrote in message
news:dgbju1hnj345uddqmf0g7ed58ss12gnaga@xxxxxxxxxx

On Wed, 8 Feb 2006 07:18:46 +0100, "Jerome" <nospam@xxxxxxxxxx> wrote:


Thanks Eric,
However concerning the 5V tolerance, i'm not sure it is necessary since
the
D+ & D- level swing
stays in the 0V - 3.6 V range

My first step will consist in measuring these levels with a scope

Those levels are OK but in USB spec there is a tolerance to short to
5V requirement which is why it's mentioned. In a controlled
environment you don't need 5V tolerance on the data inputs.
.

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