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VESA extends DisplayPort support to USB Type-C interface

Posted: 24 Sep 2014 ?? ?Print Version ?Bookmark and Share

Keywords:VESA? Alt Mode? USB Type-C? DisplayPort?

The Video Electronics Standards Association (VESA) released its Alternate Mode ("Alt Mode") standard that enables the USB Type-C connector and cable to support the DisplayPort interface and A/V transport.

Developed in liaison with the USB 3.0 Promoter Group, the standard leverages the Alt Mode functional extension of the USB Type?C interface. It repurposes some or all of the four existing SuperSpeed USB lanes to deliver full DisplayPort performancedriving monitor resolutions of 4K and beyond, SuperSpeed USB data and up to 100W of power over a single cable.

The standard also uses other signalling available in the USB Type-C connector for DisplayPort's AUX channel and HPD (hot plug detection) function. Computers, tablets, smartphones, displays and docking stations can implement the new USB Type-C connector at both ends while using the DisplayPort Standard to transmit high-resolution A/V along with USB data and power.

Devices supporting the standard can also connect to an existing DisplayPort device using a reversible USB Type-C to DisplayPort converter cable, while video source devices can use an appropriate adaptor to drive an HDMI, DVI or VGA display. All adaptors and converter cables will comply with all USB Type-C characteristics, including reversible plug orientation and cable direction.

Alt Mode standard

USB Type-C with DisplayPort alternate mode. Source: VESA

"The USB Type-C specification was developed to provide consumers with a robust connector for everything from mobile devices to PCs, and when combined with SuperSpeed USB 10Gbit/s and USB Power Delivery, it truly enables a single cable solution for the market," said Jeff Ravencraft, USB-IF President and COO. "The USB-IF is also in the process of developing joint port identification guidelines. We're working with VESA to ensure consumers can recognise when DisplayPort Alt Mode is supported on USB Type-C devices."

Like USB, DisplayPort uses a packetised data structure and differential AC-Coupled signal "lanes" that carry high speed data with an embedded clock. This allows the same electrical circuits and cables to carry either SuperSpeed USB data, at up to 10Gbit/s per lane, or DisplayPort at up to 8.1Gbit/s per lane, as defined in the DisplayPort 1.3 Standard.

Early implementations of DisplayPort Alt Mode USB Type-C devices will likely use existing DisplayPort 1.2a capabilities that support up to 5.4Gbit/s per lane. Using this speed across all four high-speed lanes will support up to 4K (4,096px x 2,160px) display resolutions at a 60Hz frame rate with up to 30bit colour.

By leveraging USB Type-C's flexibility, the standard can choose to transmit on just one or two of the four available lanes, so that the other two lanes can be used for SuperSpeed USB data at the same time. In a docking station connection, for example, the use of two lanes for DisplayPort at 8.1Gbit/s per lane would allow simultaneous transfer of SuperSpeed USB dataup to 10Gbit/s in each direction, while also supporting a 4K UHD (3,840px x 2,160px) DisplayPort monitor.

The dock can also be configured with DisplayPort protocol converters to support HDMI, VGA and/or DVI monitors. When using all four lanes for DisplayPort Alt Mode, which could drive a monitor with up to 5K (5,120px x 2,880px) resolution, USB 2.0 data can still be carried across the USB Type-C connection using separate pins dedicated for that function.

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