There’s Fast…and then There’s FAST.
A little over a year ago, Silicon Image announced the latest version of HDMI – 2.0. Among the other enhancements to this interface was an increase in the clock rate to 600 MHz, allowing data rates as high as 18 gigabits per second (GB/s).
Good thing, too, with Ultra HD televisions coming to market. The previous iteration of HDMI (v1.4) had a capped data rate of 10.2 Gb/s, which was barely fast enough for Ultra HD signals (3840×2160 pixels) refreshed at 30 Hz, with color depth not to exceed 8 bits per pixel.
By boosting the speed to 18 Gb/s, HDMI 2.0 can now pass a 60 Hz Quad HD signal – but only with 8-bit RGB color. (If you’re willing to cut the color resolution in half, you can increase the bit depth.) To me, that’s not enough of an improvement: If you’ve seen what it takes to shoot, edit, and post 4K content, you’ll realize why 10-bit and even 12-bit encoding is the way to go. But HDMI 2.0 can’t handle that with high frame rates.
Earlier this month, the Video Electronics Standards Association “officially” announced what we knew was coming for some time – DisplayPort version 1.3, which will boost its data rates to a mind-boggling 32 Gb/s – almost twice as fast as HDMI 2.0 – and also employ for the first time a form of visually-lossless compression, known as Display Stream.
Unlike HDMI, DisplayPort is a pure digital transport, using packet-based communication. It transports video, audio, metadata, and even Ethernet, using four scalable “lanes” to carry signals. In the current version (1.2), the capped data rate for each lane is 5.4 Gb/s, but with version 1.3, it will rise to 8 Gb/s.
DisplayPort’s architecture is designed to be flexible. There are full-sized and mobile versions of the connector, along with wireless and optical fiber interface specifications. Users of Apple MacBooks are familiar with the Mini DisplayPort interface, and a mobile version (Mobility DisplayPort or SlimPort) is available for tablets and phones and uses a single lane for 1080p/60 playback.
The maximum data rate for all four lanes is 21.6 Gb/s, which can accommodate a 3840x2160p/60 signal encoded with 10 bits per pixel in the RGB format. That’s considerably faster than HDMI 1.4 and one reason why a handful of TV manufacturers are adding DP 1.2 connectors to their new 4K TVs. The other reason is the lack of royalties (for now) to use the interface.
At CES, VESA announced DockPort, a multiplexed signal format that blends USB 3.0 connectivity with display signals in the standard and mini DP connectors. Now, there has been a major announcement by the USB 3.0 Promoter Group and the Video Electronics Standards Association (VESA) of something called “USB Type-C Alternate Mode.”
Drilling deeper, we find that the USB 3.0 Group has introduced a new variation of their interface, known as the Type-C connector. Unlike other versions (Types A&B and their more commonly used “full-size” and “mini” designations); the type-C connector borrows a page from Apple’s playbook and is reversible. That is; it makes no difference which way you plug it in – there is no right side or wrong side up.
There’s more: The Type-C connector (about half as large as a conventional USB Type-A connector) can carry serial data at speeds up to 10.2 Gb/s (USB 3.1 Gen 2). It can also deliver up to 100 watts of power (20 volts DC at a maximum of 5 amperes) so that a connected device could be operated while its battery charges.
There are 12 pins on a Type-C connector arrayed along both edges of the blade. Viewed from the end, the top and bottom pins are reversed from left to right, which is how you can plug it in either way and it will still work. Two pins (1 and 12) are used for ground. Pins 2 and 3 are reserved for a high-speed transmit (TX) data path, while pins 10 and 11 are reserved for a receive data (RX) path.
Pins 4 and 9 provide bus power, and pin 5 (CC) is used to communicate with the connected device to determine operating mode. Finally, pins 6 and 7 function as a USB 2.0 interface. Needless to say, the host and connected device need a USB 3.0-compatible connector switch to determine the operating mode and enable data exchange in 2.0 or 3.0 formats.
What’s unique about Type-C cables is that so-called “full feature” passive cables will actually contain an internal ID chip that signals the source connection to turn on all USB 3.0 functions and enable high-speed data exchange. These cables will be able to transmit 10.2 Gb/s of data over 1 meter (3 feet) and 5 Gb/s over 2 meters (6 feet).
Using Alternate DisplayPort mode, a maximum of four DP “lanes” of display data can travel over that same tiny USB connector, providing all the resolution and bit depth of the full-size and mini DisplayPort connectors. Or, you can reserve two lanes for USB 3.1 operation and employ the other two for displays, something you might want to do in a docking station application. USB 2.0 data exchange is always available through the same connector.
As you can see, the USB connector has gotten a lot smaller. It’s also a lot faster, and is symmetrical (no more fumbling around trying to orient the plug the right way). And it can provide the primary display connection for any device while also sending and receiving high-speed data.
With this announcement, the USB 3.0 Group and VESA have shown that “less is more” when it comes to digital signal interfacing with Type-C Alternate operation. Oh, did I mention that you will be able to buy and use a cable with a Type-C USB connector on one end and a DisplayPort plug on the other? Can’t get any easier to use than that!
Posted by Pete Putman, September 26, 2014 4:42 PM
About Pete PutmanPeter Putman is the president of ROAM Consulting L.L.C. His company provides training, marketing communications, and product testing/development services to manufacturers, dealers, and end-users of displays, display interfaces, and related products.
Pete edits and publishes HDTVexpert.com, a Web blog focused on digital TV, HDTV, and display technologies. He is also a columnist for Pro AV magazine, the leading trade publication for commercial AV systems integrators.