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I'm using this USB-to-UART IC, and this 16-pin USB-C jack on my design. I'm trying to better understand some of the USB-C spec, particularly related to pin mirroring and such.

On the PCB, should I be connecting both D+ pins to the D+ pin on the controller, and both D- pins to D-? I understand conceptually how the pin mirroring works, but I don't understand if it's expected that all cables already have them cross-wired, or if that should be done on the PCB. Conversely, if it isn't necessary, are there any pitfalls to cross-connecting them on the PCB?

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    \$\begingroup\$ Please put enough information - basic specifications, photos or drawings - into your question that it can be understood without having to follow two links. It also ensures that the question makes sense when the links die \$\endgroup\$
    – Transistor
    Apr 13, 2020 at 22:43

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They should be connected together (A6 to B6 and A7 to B7). Actually you have only one differential pair D+/D-. Because USB-C plug is flippable, there are two connections for D+ (A6 and B6) and two connections for D- (A7 and B7) on a receptacle. This way D+ is always connected to D+ and D- to D-.

USB-C Receptacle

USB-C receptacle

Image source: USB-C on Wikipedia

USB-C Plug

USB-C plug

Image source: USB-C on Wikipedia

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  • \$\begingroup\$ Right, but A6 and B6 and A7 and B7 all have separate pads, which is where my confusion comes from. Especially given that they combine V+ pins and combine GND pins, I guess I don't understand why A6/B6 wouldn't be bound to a single pad and A7/B7 wouldn't be bound to a single pad. \$\endgroup\$
    – Jesse Williams
    Apr 13, 2020 at 23:03
  • \$\begingroup\$ @JesseWilliams Sorry, that was fast and bad answer :D. I edited my answer. Hope it helps \$\endgroup\$
    – esehic
    Apr 13, 2020 at 23:48
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    \$\begingroup\$ Generally speaking a cable with "plugs" is only going to pass A6 and A7 while leaving B6 and B7 open. It is expected that the receptacle end will use CC to figure out if A6A7 are active or if B6B7 are active. But since the cable is only passing one pair you can just connect them together on the PCB receptacle side. \$\endgroup\$
    – Carl Gilbert
    Apr 14, 2020 at 0:11

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