Cool stuff about Lightning -
Lightning is adaptive.
All 8 pins are used for signals, and all or most can be switched to be used for power. So it makes no sense to say “Lightning is USB2-only” or whatever.
The outer plug shell is used as ground reference and connected to the device shell.
At least one (probably at most two) of the pins is used for detecting what sort of plug is plugged in.
All plugs have to contain a controller/driver chip to implement the “adaptive” thing.
The device watches for a momentary short on all pins (by the leading edge of the plug) to detect plug insertion/removal.
The pins on the plug are deactivated until after the plug is fully inserted, when a wake-up signal on one of the pins cues the chip inside the plug. This avoids any shorting hazard while the plug isn’t inside the connector.
The controller/driver chip tells the device what type it is, and for cases like the Lightning-to-USB cable whether a charger (that sends power) or a device (that needs power) is on the other end.
The device can then switch the other pins between the SoC’s data lines or the power circuitry, as needed in each case.
Once everything is properly set up, the controller/driver chip gets digital signals from the SoC and converts them – via serial/parallel, ADC/DAC, differential drivers or whatever – to whatever is needed by the interface on the other end of the adapter or cable. It could even re-encode these signals to some other format to use fewer wires, gain noise-immunity or whatever, and re-decode them on the other end; it’s all flexible. It could even convert to optical.