DVI - Interfaces, Cables & Adapters

The Digital Visual Interface

In order to finally establish a new video interface standard which would be acceptable to both the major systems manufacturers and display makers, the Digital Display Working Group (DDWG) was formed in 1999. The core members, known as the DDWG Promoters’ Group, was made up of seven of these companies: Compaq, Fujitsu, Hewlett-Packard, IBM, Intel, NEC, and Silicon Image.

The new standard, called the Digital Visual Interface (DVI™ 1.0) was also to be based on Silicon Image’s PanelLink or TMDS technology, and the connector chosen was very similar to the VESA P&D. The major changes from P&D to DVI included the deletion of the optional IEEE-1394 and USB interfaces, and the additional of a second TMDS data channel (three data pairs), sharing the same clock pair as the basic channel. (The additional data pairs in some cases also share the ground/return connections of the original set.) DVI also raised the question of digital content protection for the first time; while not required under the 1.0 specification, the use of an Intel-proprietary encryption system (High-Definition Content Protection, or HDCP) is officially recognized under DVI.

Physically, the DVI connectors resemble the VESA P&D, although with two fewer columns of pins and a slightly different shell design. This prevents direct physical compatibility between the two, although it is possible to connect P&D and single-channel or analog DVI with the appropriate adapters. Like P&D, DVI defined both a digital-only version (DVI-D), and one which supports both analog and digital interfaces (DVI-I), again via the Microcross ™ pseudo-coaxial connector design originated by Molex. Pinouts for both DVI versions are shown in figure below.

As of this writing, DVI has begun to see fairly widespread adoption as an LCD monitor connection, although it has yet to significantly displace the VGA connector or other options for CRT monitors, either in analog or digital form. There is also considerable interest in the standard as a possible solution for consumer television applications, for example as an interconnect between digital HDTV decoders (“set-top boxes”) and digital-input receivers. The support for digital content protection provided by DVI (the HDCP encryption system) is of particular interest in such applications. However, there remain some open issues within the DVI specification, which are being addressed by a joint effort between the DDWG and several consumer electronics manufacturers and their industry association, the CEA. Among these are the need for audio support and the possibility of alternate color encoding methods, such as a “YUV” or similar encoding rather than the DVI-standard RGB. The DDWG is also working on some implementation concerns which have been raised by the computer industry, such as the use of DVI as a display input connector and the standard means for transitioning between single- and dual-channel TMDS support. The former is a concern due to the possibility of different display capabilities being available depending on whether the analog or digital interface is in use – yet the display can only provide a single set of ID information at a time. The use of the second TMDS channel is also problematic under the current specification. While the DVI 1.0 standard set 165 MHz as the limit for the basic single-TMDS version, it did not set explicit guidelines for managing both single- and dual-channel operation within a given system. The second channel could potentially be used for supporting larger display/image formats, increased “color depth” or both – but how this is to be negotiated between the display and host has not yet been well defined.

Still, even with these minor concerns, DVI at this point represents the interface most likely to win widespread adoption within not only the computer display industry, but beyond it to consumer applications as well. Development of the standard will no doubt continue for some time, but there seems to be enough momentum building behind this latest standard to ensure at least success beyond that achieved by the earlier attempts.

DVI Cables & Adapters

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