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If i design a PCB(1) with a type B USB 3.0 connector on it and use a Type A to B cable to connect my board to a standard personal computer with type A USB 3.0 connector do i have to swap the RX and TX pairs on my board? Furthermore, if i connect my PCB(1) to another PCB(2) and put a Type A connector on that new PCB(2) do i have to swap the pairs on the new or old PCB(1)? If i plug a standard usb thumb drive into the new PCB(2) will it work without swapping the RX and TX pairs on either of the boards?

Sorry if this is confusing i am just trying to figure out whether a type A to type B USB 3.0 cable swaps the pairs or not. And if i design a board that is essentially a male to male extension cable but use a type A to type B cable in that path whether i still have to swap the RX and TX pairs or not.

Thanks!

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  • \$\begingroup\$ Now I'm confused .. although "USB male-to-male extension cable" is not a thing that should be built. \$\endgroup\$ – pjc50 Mar 6 '15 at 16:56
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USB 3.0 added 2 additional differential pairs. The two additional "SuperSpeed" pairs are uni-directional like PCIe. The Tx of the device has to go to the Rx of the host. So, if you are the device-side (B), your Tx+/- will go to the host-side (A) Rx+/-. The cable itself is straight pass-through.

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USB uses differential data transmission with receive and transmit sharing the same pair of wires so if they became reversed it won't work .

Protocols like RS232 have a wire for transmit and another wire for receive. Were you, perhaps anticipating USB to be identical?

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Now I'm confused .. although "USB male-to-male extension cable" is not a thing that should be built.

I think the answer is "no". Part of your confusion is calling the wires RX and TX, when they're actually called D+ and D-. As long as you keep D+ connected to D+ and D- connected to D- it should work.

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  • \$\begingroup\$ USB 3.0 has three differential pairs: D+/D-, SSTx+/SSTx-, and SSRx+/SSRx-. \$\endgroup\$ – duskwuff Mar 6 '15 at 23:46

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