USB 3.0 has 9 wires.
4 from USB 2.0 (VCC, GND, D+, D-)
+ 5 new for super (SSTX+/-, SSRX+/-, GND)

My Understandings: (these may not be correct)
- USB 3.0 is separated from USB 2.0 and USB 3.0 doesn't use D+/- for data transmission.
- USB 3.0 Hub structure shows different path between 2.0 and 3.0.
- From USB 3.0 Speed detection procedure, D+/- are not needed once 3.0 speed setup.

I did a experiment to know whether D+/D- can be ignored by 3.0.

  • I bought a USB 3.0 extension cable, and verify the cable works fine with USB 3.0 memory and USB 3.0 hub.
  • I cut D+/D- 2.0 data lines in the middle of the extension.
  • There was no USB 3.0 connection. no 2.0 of course.
  • I re-bind D+/D- data lines, connection was recovered in both 3.0 and 2.0.
  • While connected, cut any of D+ or D- makes connection lost.

    From my experiment, D+/D- cannot be ignored even for 3.0 from plugging-in to operating.

    Recently lightning cable to USB type C released, and iPad Pro supports 3.0 speed.
    lightning cable has 4 data lines: D1, D2, D3, D4.
    I'm wondering how it makes USB 3.0.

    Please correct if there's any wrong info.

  • \$\endgroup\$
    • 5
      \$\begingroup\$ USB 2.x and 3.x devices startup and enumerate using the original USB 1.x signalling, then switch over to faster clocks later (negotiated by both ends). \$\endgroup\$
      – Ben Voigt
      Mar 24, 2016 at 2:09
    • \$\begingroup\$ Been looking for this whole day. Would be nice to include some other words to find this easier. Also, would be nice if @BenVoigt you could provide extended answer and weight to your statement. The OP asked how the iPad can make USB 3 connection using 4 pins, while you stated they use old pins to negotiate first, which does not fit. As far as apple goes though, my guess would be the negotiation part is made by the converter...? \$\endgroup\$
      – That Marc
      Apr 7, 2016 at 12:48
    • \$\begingroup\$ You can get lightning to USB 3 converters, but they are active cables. They have controller ICs which convert from whatever proprietary protocol apple use to the USB protocol. \$\endgroup\$ Apr 22, 2016 at 13:24

    2 Answers 2


    Device enumerating at USB 3.1 (The specification has been updated to USB3.1, defining Gen1 (5Gbps) and Gen2 (10Gbps)) first enumerating in USB 2.0 mode.The Host switches to Superspeed mode only after retrieving device configuration descriptors in USB 2.0 mode. So, USB 2.0 must be supported, i.e. wires connected.

    It is not allowe by spec to not support the USB2.0 functionallity: Peripheral Devices

    A USB 3.1 peripheral device must provide support for both Enhanced SuperSpeed and at least one of the USB 2.0 speeds. The minimal functional requirement for the USB 2.0 speed implementation is for a device to be detected on a USB 2.0 host and allow system software to direct the user to attach the device to an Enhanced SuperSpeed port. A device implementation may provide appropriate full functionality when operating in the implemented USB 2.0 speed mode. Simultaneous operation of Enhanced SuperSpeed and USB 2.0 speed modes is not allowed for peripheral devices.

    USB 3.1 wires can be left unconnected - this is identical to attaching device to Host USB 2.0 port.

    For the lightning question, it is correct that the Ipad pro supports 3.1 Gen1, according to the internet. Now the current lightning cables only have the limited amount of of data lines and therefor they do not support USB3.1 Gen1 but only USB2.0 High speed. I am currently not sure if Apple is planning on bringing modified Lightning Cables to support USB3.1 Gen1 and therefor the converters to USB Type-C connectors/cables

    • \$\begingroup\$ Could you connect the 2.0 pins via a 2.0 hub to the host, while directly connecting the 3.0 pins to a host? (that way you could use have many 2.0 ports and a single 3.0 port) \$\endgroup\$
      – jdizzle
      Jun 23, 2021 at 15:17

    Your question boils down to "how does a Lightning-to-USB3.0 adaptor work when there's not enough wires on the Lightning side?"

    The answer is that Apple have hidden a processor in the cable. This makes it possible to dynamically reinterpret the signals. It most likely speaks an Apple proprietary protocol on the Lightning side and implements the USB3.0 host on the chip in the cable.

    • \$\begingroup\$ Not only cable but also iPhone/iPad needs a chip handling wires. </br> USB 3.0 lightning cable may have at least 4 more wires, and chip on the cable and in the iPhone/iPad handling 4 wires. \$\endgroup\$
      – Doojin
      May 16, 2016 at 7:40

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