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Jeff Wexler

Lightning Connector

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After all the complaining about the new connector on the iPhone 5, there have been some significant revelations about this connector. These explanations go far beyond the remarks about how Apple used the new connector just to keep us buying new stuff and how awful it is that Apple has pissed off all the accessory companies. It looks to be a truly "smart" cable with active adaptive components that configure its use.

Apple's Lightning Connector Uses Adaptive Technology to Dynamically Assign Pin Functions

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With Apple's new Lightning connector on the iPhone 5 dropping to just eight contact pins from the 30 pins seen in the original dock connector and gaining the ability to be inserted in either orientation, many have wondered just how Apple has been able to maintain most of the functions of the original dock connector. Others have wondered why Apple simply didn't shift to micro-USB, an existing standard in a comparable form factor.

Developer Rainer Brockerhoff has been examining Lightning's technical features and over the weekend outlined his thinking on how the "adaptive" nature of the Lightning connector highlighted by Apple during the technology's introduction at the iPhone 5 media event has enabled flexible functionality with a minimum of pins. Brockerhoff notes that the Lightning connector appears able to sense what kinds of devices are being connected and to use chips embedded in the cable to assign pin functionalities appropriate for each situation.

- 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.

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This information is still just ruminations of some random guy on the internet. The official spec has nothing to say about the actual signals that go between the iPhone and the connector, and even if they did, the NDA prevents people who want to build anything Apple compliant in the future from talking about it.

Tom.

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This information is still just ruminations of some random guy on the internet. The official spec has nothing to say about the actual signals that go between the iPhone and the connector, and even if they did, the NDA prevents people who want to build anything Apple compliant in the future from talking about it.

Tom.

This has nothing to do with NDA and it is not "ruminations of some random guy" but rather a fairly thorough and detailed analysis with real world testing of this new connector and new adaptive connection protocol. I am not going to post the entire article but here is a little bit more from this "random guy on the Internet" :

Here’s where

the old “wires-all-the-way-down” reflexes kick in, at least if you’re not a hardware engineer. To quote from that link:

Although it’s clear at this point that the iPhone 5 only sports USB 2.0 speeds, initial discussions of Lightning’s support of USB 3.0 have focused on its pin count—the USB “Super Speed” 3.0 spec requires nine pins to function, and Lightning connectors only have eight.

…The Lightning connector itself has two divots on either side for retention, but these extra electrical connections in the receptacle could possibly be used as a ground return, which would bring the number of Lightning pins to the same count as that of USB 3.0—nine total.

(…followed, in the comments, by discussions of shields and ground returns and…)

Of course, that contains the following failed assumptions (beyond what I just mentioned):

  • Lightning is just a USB3 interface in disguise, and
  • Cables and connectors are always wired straight-through, at most with a shield around the cable.
  • If there are any chips in the connector, they must be sinister authentication chips!

These assumptions also underlie the oft-cited intention of “waiting for the $1 cables/adapters”. But, recall that Apple specifically said that Lightning is an all-digital, adaptive interface. USB3 is not adaptive, although it can be called digital in that it has two digital signal paths implemented as differential pairs. If you abandon assumptions 1 and 2, assumption 3 becomes just silly. Remember, the SlimPort designers put a few simple digital signals on the connector and converted them – just a cm or so away – into another standards’ differential wire pairs by putting a chip inside the plug.

So, summing up all I said here and

in my previous posts:

  • 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.

I’ll be seriously surprised if even one of those points is not verified when the specs come out. And this is what is meant by “future-proof”. Re-using USB and micro-USB (or any existing standard) could never do any of that.

Update: just saw this article which

purports to show the pinouts of the current Lightning-to-USB2 cable. “…dynamically assigns pins to allow for reversible use” is of course obvious, if you put together the “adaptive” and “reversible” points from this picture of the iPhone 5 event. Regarding the pinout they published, it’s not radially symmetrical as I thought it would be (except for one pin), so I really would like a confirmation from some site likeiFixit (I hear they’ll do a teardown soon). They also say:

Dynamic pin assignment performed by the iPhone 5 could also help explain the inclusion of authentication chips within Lighting cables. The chip is located between the V+ contact of the USB and the power pin of the Lightning plug.

I really see no justification for the “authentication chip” hypothesis, and even their diagram doesn’t show any single “power pin of the Lightning plug”. It’s clear that, once the cable’s type has been negotiated with the device, and the device has checked if there’s a charger, a peripheral or a computer on the other end, the power input from the USB side is switched to however many pins are required to carry the available current.

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This has nothing to do with NDA and it is not "ruminations of some random guy" but rather a fairly thorough and detailed analysis with real world testing of this new connector and new adaptive connection protocol. I am not going to post the entire article but here is a little bit more from this "random guy on the Internet" :

Already read it, smart guy, but if he'd seen the official documents, he wouldn't need to guess so much.

It's obvious what information is missing, and I believe that Apple expended a lot of man power to make it hard to reverse engineer to a working copy, if not impossible.

Tom.

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It's impressive but seems over engineered to me.

I think Apple's main incentive for developing this is to make it stand out as different and more special than Android and other phones.

The common micro USB connector can do a lot too. Charge, exchange data, interface with other devices, share an internet connection, etc.

Not trying to start a war, I just don't see the lightning connector being that fundamentally different.

I will say that it is cool the plug will fit either way.

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