Electronic – USB 3.0 wires for data transmission

lightningusb

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.

    • Best Answer

    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:

    3.2.6.1 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

    Related Topic