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DVI explained
DVI explained. DVI used with D-ILA Projectors.

DVI explained

WHAT IS DVI ?

Short for Digital Visual Interface, a digital interface standard created by the Digital Display Working Group (DDWG) to convert analog signals into digital signals to accommodate both analog and digital monitors. Data is transmitted using the transition minimized differential signaling (TMDS) protocol, providing a digital signal from the PC's graphics subsystem to the display. The standard specifies a single plug and connector that encompass both the new digital and legacy VGA interfaces, as well as a digital-only plug connector. DVI handles bandwidths in excess of 160 MHz and thus supports UXGA and HDTV with a single set of links. Higher resolutions can be supported with a dual set of links.

DVI is a new form of video interface technology made to maximize the quality of flat panel LCD monitors and high-end video graphics cards. It is a replacement for the P&D Plug & Display standard, and a step up from the digital-only DFP format for older flat panels. DVI is becoming increasingly popular with video card manufacturers, and most cards purchased include both a VGA and a DVI output port.

In addition to being used as the new computer interface, DVI is also coming out as the digital transfer method of choice for HDTV, EDTV, Plasma Display, and other ultra-high-end video displays for TV, movies, and DVDs. Likewise, even a few of the top-end DVD players are now featuring DVI outputs in addition to the high-quality analog Component Video.

WHAT ARE THE DVI FORMATS ?

There are three types of DVI connections:

DVI-D (Digital)
DVI-A (Analog)
DVI-I (Integrated Digital & Analog)

DVI-D - True Digital Video DVI-D format is used for direct digital connections between source video (namely, video cards) and digital LCD (or rare CRT) monitors. This provides a faster, higher-quality image than with analog, due to the nature of the digital format. All video cards initially produce a digital video signal, which is converted into analog at the VGA output. The analog signal travels to the monitor and is re-converted back into a digital signal. DVI-D eliminates the analog conversion process and improves the connection between source and display.

DVI-A - High-Res Analog DVI-A format is used to carry a DVI signal to an analog display, such as a CRT monitor or an HDTV. Although some signal quality is lost from the digital to analog conversion, it still transmits a higher quality picture than standard VGA.

DVI-I - The Best of Both Worlds DVI-I format is an integrated cable which is capable of transmitting either a digital-to-digital signal or an analog-to-analog signal, but it will not work transmitting a digital-to-analog or analog-to-digital signal.

Like any other format, DVI digital and analog formats are non-interchangeable. This means that a DVI-D cable will not work on an analog system, nor a DVI-A on a digital system. Make sure that you know what format each part of your equipment is before you purchase any DVI cables.

Only equipment with a DVI port labeled 'DVI-I' will accept both a DVI-D and DVI-A source signal.

WHAT ARE SINGLE AND DUAL LINKS ?

The Digital formats are available in DVI-D Single-Link and Dual-Link as well as DVI-I Single-Link and Dual-Link format connectors. These cables send information using a digital information format called TMDS (transition minimized differential signaling).

Single link cables use one TMDS 165Mhz transmitter, while dual links use two. The dual link effectively doubles the power of transmission and provides an increase of speed and signal quality; i.e. a single link 60-Hz LCD can display a resolution of 1920 x 1080, while a dual link can display a resolution of 2048 x 1536.

HOW DO I KNOW WHICH CABLE TO USE?

Determining which type of cable to use for your DVI products is critical in getting the right product the first time. Check both of the female DVI plugs to determine what signals they are compatible with.

Note: To prevent pins being broken off of mistmatched cables, most manufacturers will make their female plugs with all available pins. This means that many female DVI plugs may look like a DVI-I, but this is not necessarily true. Be sure to look for a label, or check the product documentation to make sure you know what type it is.

IN BRIEF

If you have plugs that are DVI-D, they will accept a DVI-D cable.

If you have plugs that are DVI-A, they will accept a DVI-A cable.

If you have plugs that are DVI-I, they will accept any type of DVI cable.

If you have mistmatched plugs, such as DVI-D and DVI-I or DVI-A and DVI-I, you may use either a DVI-I cable or the cable that matches the other plug. For example, you may use a DVI-D cable on a DVI-I to DVI-D connection, but not a DVI-A cable.

Note: You may not mismatch a DVI-D and a DVI-A connection.

It is possible to extend existing DVI cables by the use of DVI-I extension and DVI-D Extension cables. The maximum signal length, however, is 5 meters, and going beyond that may result in quality loss.

For a list of common brand-name flat panel displays, projectors, video cards,and other products, check out the DataPro DVI Product Reference Page.

HOW TO RECOGNIZE A DVI CABLE

There are two variables in every DVI connector cable, and each represents one characteristic:

The flat pin on one side denotes whether the cable is digital or analog:
- A flat pin with four surrounding pins is either DVI-I or DVI-A
- A flat pin alone denotes DVI-D
The pinsets vary depending on whether or not the cable is single- or dual-link:

A solid 24-pin set (rows of 8) for a dual- link cable
Two separated 9-pin sets (rows of 6) for a single-link cable

Note:

1. To distinguish between DVI-I and DVI-A, always check the pinset:

A solid 24-pin set is for a DVI-l
A separated 8-pin and 4-pin set is for DVI-A

2. DVI was originally designed to be fully cross-compatible, but many manufacturers are creating DVI-I cables with a wider flat pin than the DVI-D cables, reducing compatibility.