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USB decoding with single channel

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USB decoding with single channel

Postby droberts » Mon Jul 31, 2017 2:28 pm

Hello, I am making good use of the PicoScope 6 USB 12Mbit decode (on a 3406DMSO). But I was wondering if it is possible to decode using just a single scope channel. I have a differential probe, and can get a clean signal on one channel using that. And often just a single-ended signal is "good enough" for decoding, and saves having to clip two probes, and use two channels.

If there is some "trick" in the GUI to force it to use just one channel, I cannot figure it out. It seems to always require two channels, else it does not decode.
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Re: USB decoding with single channel

Postby Gerry » Wed Aug 09, 2017 12:37 pm

Hi, dale,

A previous USB decode implementation in the original Serial Decoder only decoded one channel, but had serious problems performing the decode correctly, which is part of the reason why we now only use differential channels. Obviously, if you are effectively decoding only one Channel, you are going to change the loading on one differential channel, and potentially increase the susceptibility of the channel to noise and other induced signals.

However, if you must try this then you could try creating a Math channel that is -A and then use Channel A and the Math channel as your D+ and D- signals. Alternatively, if there is an issue with the order of post processing between Serial Decoding and Maths Channels, you could try using a Digital channel for D- and just grounding it.

I don't have a USB 1.0/1.1 device or data stream to test this, but then this isn't something that I would recommend doing for reliable USB decoding.


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