Monday, March 25, 2013

Digital Video Interface (DVI) - Simplified For the Rest of Us

A camel is a horse designed by a committee. It can be argued the same for the DVI standard as developed by Digital Display Working Group (DDWG) in 1999. This standard was developed as a replacement for a long-standing VGA standard.

There are a total of Six different types of DVI Connectors:

1 - DVI-A

2 - DVI-D Single Link

3 - DVI-D Dual Link

4 - DVI-I Single Link

5 - DVI - I Dual Link

6 - M1-DA Integrated D, A and USB.

Before we get any further, in the above, A stands for analog, D stands for Digital and I stands for Integrated. Unfortunately, many of these connectors are not compatible with each other. Hence, it is important to only acquire DVI cables after confirming the type that will be compatible with your system. Also, unlike HDMI, DVI cables carry no audio signal.

The maximum resolution that can be displayed depends on the Refresh rate (written with the "Hz") and the display device mode being used e.g. HDTV, SXGA and WQUXGA etc. The difference between Single Link and Dual link is that Dual Link displays 2 pixels per cycle clock as opposed to 1 pixel per cycle clock. Hence with DVI-Dual Link, you get two times the information per cycle for each pixel, resulting in higher quality display.

In order to get the right cable the first time, one must check the female DVI connectors at the source and the display to establish what signals they are compatible with. Below we show which cables are compatible for a given connectors:

1 - DVI-A Cable à if one or both connectors are DVI-A

2 - DVI-D Cable à if one or both connectors are DVI-D

3 - DVI to VGA Cable à if one connector is DVI-A, while the other is VGA (15 pin Computer Monitor connector)

4 - DVI-I to DVI-I Cable à If both connectors are DVI-I. Although, any DVI cable will work, DVI-I cable is preferred.

5 - If one of the two connectors is Analog, than a direct cable cannot be used for connecting the source to the display. A converter box must be used to convert the digital signal to analog for display. However, keep in mind that due to Digital Rights Management (DRM), it is currently NOT legal to make or sell converters for Digital DVI or HDMI signal to Analog signal (VGA or Component), at least in the United States.

DVI Standard was developed as a replacement for the VGA standard, hence it was primarily designed for the computers that are rarely away from the source. However, as a home theater video display standard, users frequently have to run longer lengths of wire. Consequently, most DVI cables will support a strong signal for up to 4.5m for higher resolutions, however as this distance increases the maximum supportable resolution drops. Users have reported using up to 10m long DVI cables without noticeable signal loss. DVI boosters may be necessary for longer cable runs. Occasionally, certain situations may require a custom cable manufacturer for custom length and connector based cables.

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