Apple’s Lightning Digital AV Adapter

Recently, Panic noticed the odd output resolution and MPEG-like artifacts with the new Lightning digital AV adapter and decided to take a hacksaw to it. They found an ARM processor inside.

Lightning digital AV adapter

image credit: Panic blog

Shortly after, they received an anonymous comment that explains it all:

The reason why this adapter exists is because Lightning is simply not capable of streaming a “raw” HDMI signal across the cable. Lightning is a serial bus. There is no clever wire multiplexing involved. […] We did this to specifically shift the complexity of the “adapter” bit into the adapter itself, leaving the host hardware free of any concerns in regards to what was hanging off the other end of the Lightning cable.

This system essentially allows us to output to any device on the planet, irregardless of the endpoint bus (HDMI, DisplayPort, and any future inventions) by simply producing the relevant adapter that plugs into the Lightning port. Since the iOS device doesn’t care about the hardware hanging off the other end, you don’t need a new iPad or iPhone when a new A/V connector hits the market.

While I understand what they are trying to achieve, I think it’s sad that this new Lightning system can no longer carry the uncompressed HDMI output. Maybe they could have streamed the raw video output in a format close to what HDMI expects, then have the adapter add headers and trailers to the data, but that would still be tricky since the system needs to stop sending frames while the adapter is doing its work. And what about HDCP?

Just one of the many tradeoffs that engineers need to make.

The Apple 30-pin Dock Connector

The 30-pin dock connector first appeared on the iPod 3G in 2003, and has been on all iPods, iPhones and iPads ever since, with the sole exception of the first generation iPod Shuffle. The first gen Shuffle looks like a thumbdrive (or what some would call a pen drive) and used a USB male connector, whereas the first and second generation iPods had a FireWire port at the top.

iPod Accessory Protocol

Since its introduction, Apple made several minor modifications to the electronics interface of the dock connector, but the physical connector itself remains unchanged. Collectively, this and the communications protocol is called the iPod Accessory Protocol (iAP).

Initially, they introduced different resistor values on the “accessory detect” pin when they allowed third-party companies to make docks and car adapters. At that time, the dock connector mainly had audio in and line out functionality (connected to the back of the docks), as well as a serial interface for remote control via the dock. The serial protocol was largely reverse-engineered by maushammer (website no longer accessible) and this guy here (I think he’s called Christoph but it’s not on that page). This was also used by car manufacturers to allow iPod playback control from buttons on the steering wheel.

When Apple released the iPod Video that was capable of playing videos in 2005, they added video out (composite and S-video), as well as an authentication chip to allow only authorized docks and cables to receive video out (including audio). Soon enough, China caught up with their release of “authorized” accessories, which contain the authentication chip that can be re-purposed for other use.

Authentication chip (image from

Presumably, that was also when they added USB support for iAP, which I’m pretty sure also requires an authentication chip. USB support would allow a host to communicate and control the iPod through a USB cable. My car stereo correctly recognizes the iPhone as an iPod over a USB cable.

The iPod Camera Connector was also introduced for the iPod Photo and iPod Video in 2005. This was a small “dongle” that has a dock connector on one end and a USB port on the other. Oddly, according to an Everymac article, later iPods released in 2006 do not support this accessory any more. It is unknown if they somehow switched the USB interface to host mode, or if they used a separate chip to emulate this.

In 2008, charging via FireWire was no longer supported with the introduction of the 2nd generation iPod Touch and 4th generation iPod Nano. The pins dedicated to FireWire in the dock connector are now unused.

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Enable iOS 5 Multitasking Gestures on iPad 1

Now that iOS 5 has been released, it’s easy to enable multitasking gestures on the iPad 1, using the same trick as before for display mirroring.

Edit the /System/Library/CoreServices/ file and add a boolean key multitasking-gestures in the capabilities dict, and set its value to true. You can add both display mirroring and multitasking gestures to the iPad 1 using this method.

That’s it!

Alternatively you can use Cydia or redsn0w to do this for you.