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Understanding DVI-D, HDMI, DisplayPort & USB Connections

A basic primer for integrators on TMDS-based connections like HDMI or DVD-D, USB and DisplayPort connections for distributing digital video signals.


In mathematics, computer science and even in philosophy, convergence refers to the idea that change is a confluent path.  If we understand how analog and digital technological convergence, in the context of analog sunset, affects the ways we’ll communicate in the future, then we’ll be in a position to provide valuable market differentiation that will result in better business outcomes. A thorough knowledge of the intricacies of emerging digital A/V signal trends will allow us to effectively counsel customers to efficient, dependable, and satisfying A/V solutions.

A quarter of a century ago almost all video and electronics engineers thought digital television defied the laws of physics.  In 1990 “digitizers”, which were excruciatingly expensive and complex experimental components, were only capable of storing about 10 seconds of very low quality video content.  Today we fully expect to be able to watch HD video content on a smart phone!  This progress is a direct result of IT-AV convergence; an irresistible force that is currently rendering the analog connectivity of yesterday hopelessly irrelevant.

To prosper in the coming decade, A/V professionals must be conversant in the application of a small handful of new digital connectivity systems. TMDS, transition minimized differential signaling, is the basic algorithm underlying all DVI-D and HDMI technology. TMDS content flows like a river of red, green, and blue bits that are superficially similar to the RGBHV of our analog video past. TMDS leverages a magical quality of digital technology; the ability to make signals easier to transport and use by adding bits to the raw samples in the form of 8b/10b mapping.

TMDS is the de facto standard for accessing broadcast content by getting A/V signals out of components such as DVD players, digital video recorders and set-top boxes. Both HDMI and DVI-D leverage identical TMDS standards. TMDS is also the core for extending the connectivity of digital AV content beyond 300-feet via HDBaseT networking.

DisplayPort is a digital display interface developed by the Video Electronics Standards Association (VESA) and it relies on packetized data transmission like that used for PCIe, Ethernet and USB. It is the technology designed to move A/V content from the confines of a computer’s hard drive to the external world, and has the amazing ability to recognize and adapt to the TMDS environment. DisplayPort won’t replace HDMI; it will continue to grow in partnership, as the “compute” flip side of the TMDS coin.

In December of 2010 AMD, Dell, Intel Corporation, Lenovo, Samsung Electronics and LG Display all announced their intentions to accelerate the adoption of TMDS and DisplayPort connections in both source and display products. By the end of 2015 it is a safe bet that analog connectivity, including today’s common VGA connections, will be a thing of the past. The sun is setting on analog. The A/V technology that illuminated our world for more than half a century will soon be nothing more than a historical curiosity. If you want to survive and thrive in light of a new digital day it’s imperative that you have a solid understanding of DVI-D, HDMI, DisplayPort and USB technologies. Your business depends on it.





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Article Topics

News · Wire and Cable · HDMI · All topics

About the Author

Joseph Cornwall
Joseph Cornwall, CTS, is the technology evangelist at C2G.

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