From: dan@djph.net   
      
   On 2024-03-19, Andrew Smallshaw wrote:   
   > On 2024-03-13, Dan Purgert  wrote:   
   >> On 2024-03-12, Roger Hayter wrote:   
   >>> On 12 Mar 2024 at 19:27:04 GMT, "Dan Purgert"  wrote:   
   >>>>   
   >>>> There's only one set of pins (well, two sets if you count USB2 / USB3 --   
   >>>> but you can only use one set at a time).   
   >>>>   
   >>>> USB2 -> D+/D- (Bi-directional / Half Duplex)   
   >>>> USB3 -> TX1+/TX1- and RX2+/RX2- (optionally Full Duplex, IIRC)   
   >>>>   
   >>>> As I recall the "Tx" pair is "Host Transmit to Peripheral", and "Rx" is   
   >>>> "Host Receive from Peripheral", but it's been a while since I read up on   
   >>>> the USB3 / USB-C implementations.   
   >>>   
   >>> Usbc seems to have about 20 pins, that's why I asked.   
   >>   
   >> Yeah, that's just to allow the connector to be flipped over, and still   
   >> connect to the host / peripheral.  The host/peripheral ports themselves   
   >> only have one orientation.   
   >   
   > USB-C supports SuperSpeed which uses two additional pairs on top   
   > of USB2 and also allows for full-duplex.  That is what the additional   
   > contacts on a USB3 A plug are for.   
   >   
      
   Except what Roger is talking about is the "spare(tm)" contacts in a   
   USB-C cable :   
      
      
     GND TX1+/- VBUS CC1 D+/- SUB1 VBUS RX2-/+ GND <-- Used   
      
     GND RX1+/- VBUS SUB2 D-/+ CC2 VBUS TX2-/+ GND <-- "spare(tm)"   
      
      
   And that's assuming all the wires are actually *in* the cable, and the   
   manufacturer didn't just cheap out and common things "vertically" (e.g.   
   TX2+ is common to  RX2+, like in "Amazon Basics" cables).   
      
      
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