Electronic – Do USB 3.0 male-to-male A-to-A cables swap SSTX and SSRX

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There are many USB 3.0 Type A male-to-male cables on the market (example on Amazon), but I can't find any information on whether they would switch the SSTX and SSRX lines, so that the SSTX pins on one side reach the SSRX pins on the other side and vice versa, or if they connect SSTX to SSTX and SSRX to SSRX instead.

I know that A-to-B cables have opposing pinouts for SSTX and SSRX, so I suspect that in that case the SSTX pins on the A site go to the SSRX pins on the B side, but I'm not sure whether this maps to A-to-A cables.

Is there a standard for this? How are they wired?

Best Answer

This cable is specified in section 5.5.2 of the USB 3.0 specification, which is available from USB.org. I've included a screenshot below, but the short version is:

  • VBUS and the USB2 signals (D+ and D-) are not connected.
  • The TX and RX lines are crossed in each pair.

Note that this is a special-purpose cable. (The standard suggests "operating system debugging" as an example application.) It cannot be used to connect normal devices.

enter image description here

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