People keep asking why Apple didn’t opt for the micro-USB connector. The answer is simple: that connector isn’t smart enough. It has only 5 pins: +5V, Ground, 2 digital data pins, and a sense pin, so most of the dock connector functions wouldn’t work – only charging and syncing would. Also, the pins are so small that no current plug/connector manufacturer allows the 2A needed for iPad charging.
This takes us back to the sensing circuitry referred to. If one of the pins is reserved for sensing – even if it is the “dumb” sensing type that Apple has used in the previous generation, using resistors to ground – and two pins are mapped directly to the 2 USB data pins, the other 5 pins can be switched at will to whatever function is necessary. For instance, if the USB-to-Lightning cable is used, the data pins can signal whether the USB side is plugged to a charger or to a computer’s USB port, and the other 5 pins can be used for charging current without overloading any single pin.
This also explains the size (and price) of the Lightning-to-30 pin adapter. It has to demultiplex the new digital signals and generate most of the old 30-pin signals, including audio and serial transmit and receive. The adapter does say “video and iPod Out not supported”; I’m not sure if the latter refers to audio out, though I’m now informed that the latter exports the iPod interface to certain car dashboards.
It’s as yet unknown whether Lightning will, in the future, support the new USB 3.0 spec – the current Lightning to USB cable supports only USB 2.0. This would require 4 (instead of 2) data pins, which is well within the connector’s capabilities. But would the mobile device’s memory, CPU and system bus support the high transfer rate? My guess is, not currently. Time will tell.
