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AnsweredHot!USB 3.1 Single Data channel vs C connector dual data channel.

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kaipyroami
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2020/07/05 09:06:57 (permalink)
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USB 3.1 Single Data channel vs C connector dual data channel.

Hi, I have a question regarding the use of a USB C connector with the LAN7801 IC.
The type C connector has two SS data channels while the 7801 only has one.
In this case is only TX1/RX1 used and TX2/RX2 is left unconnected?
Or do I tie both channels together since the type C connector can be flipped? (TX1-2/RX1-2)
 
 
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mbrowning
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Re: USB 3.1 Single Data channel vs C connector dual data channel. 2020/07/05 10:23:49 (permalink) ☄ Helpfulby kaipyroami 2020/07/05 11:06:52
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I believe both connector pin pairs are tied the same wire pair, so you can use either pin pair on your PCB.
 
edit - this is for the 2.0 pair
post edited by mbrowning - 2020/07/05 12:06:13
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kaipyroami
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Re: USB 3.1 Single Data channel vs C connector dual data channel. 2020/07/05 11:02:35 (permalink)
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Ok, I guess that makes sense since a USB C to A cable would only have one SS channel
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mbrowning
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Re: USB 3.1 Single Data channel vs C connector dual data channel. 2020/07/05 11:20:37 (permalink)
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The two usb 3 pair sets are separate, however, and the active pair is usually selected by switches on the host side through one or two signal wires. I forget the exact details but had to go through this a year ago.
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kaipyroami
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Re: USB 3.1 Single Data channel vs C connector dual data channel. 2020/07/05 11:25:09 (permalink)
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Ah ok. So if I only use one pair, say TX1/RX1 then the host will determine what pair is functional.
Got it
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mbrowning
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Re: USB 3.1 Single Data channel vs C connector dual data channel. 2020/07/05 12:22:56 (permalink) ☼ Best Answerby kaipyroami 2020/07/05 12:24:46
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I reviewed our schematic from last year. The D+ and D- pins are to be connected together on the device. For the SS connection, just use one TX and RX set and pull the associated CC pin low with 5.1K. So if you connect TX1+/- and RX1+/-, pull CC1 low. This is what tells the host which pair is in use and it will connect the correct pair through a DPDT switch on it's end.
 
This was on a colleague's design. I'm not sure the SS connection was ever tested as the LAN7800 was a contingency he wanted to include for some reason.
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kaipyroami
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Re: USB 3.1 Single Data channel vs C connector dual data channel. 2020/07/05 12:30:09 (permalink)
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This was immensely helpful, thank you!
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