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Dvi Faq

Discussion in 'Projectors, Screens & Video Processors' started by nunew33, Oct 22, 2003.

  1. nunew33

    nunew33
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    Found this useful from http://www.hallresearch.com/products/cables/video/dvi.htm

    WHAT DOES DVI STAND FOR?

    DVI means Digital Visual Interface.

    DVI is the most recent video interface designed to optimize the quality of a PC's image on a flat panel LCD. It is a replacement for the short lived P&D (Plug & Display) standard and a step up for the DFP format for first generation fully digital flat panels. Slowly DVI is becoming more and more popular with video card manufacturers, and most video cards today include both VGA and DVI outputs.

    ARE THERE DIFFERENT DVI FORMATS ?

    Yes. There are at least three common types of DVI connections:

    DVI-D (Digital) - Subdivided in single and dual link

    DVI-A (Analog)

    DVI-I (Integrated Digital/Analog)

    DVI-D - Fully Digital

    DVI-D is used for direct digital connections between the video card and digital LCD. Theoretically this would offer a higher quality image than would be possible with analog (VGA). Internally, the video image generated by your computer is in digital format, to output the image to a monitor the video cards used to convert this digital information into RGB analog signals and send them to a monitor on a "multi-coaxial" cable. All CRT monitors are quite happy to use this analog signal directly because inside they employ analog circuits. However to display the VGA image on an LCD, the LCD has to first convert the information back into digital format (by high speed sampling). Most LCD's do a great job of this but the idea behind DVI is to eliminate this double conversion to analog and back.

    The drawback to this is that since the clock rates of the signals inside the cable are extremely high (several hundred mega bits per second), this puts a high demand on the construction of the DVI cable (shielding, twisting, impedance match, etc) and places a relatively severe limitation on the cable length (15 ft max). This makes DVI suitable for desktop use but not so great for use in switching splitting and transmitting over long distances (though all this is still possible given enough $$$)

    SINGLE-LINK OR DUAL-LINK THAT IS THE QUESTION!

    The DVI-D and DVI-I formats (described below) are available in either Single or Dual link formats. Dual-Link cables are backward compatible with Single-Link cables and allow you to achieve very high resolutions if your video card and LCD support it. The general rule of thumb is that single link cables are good to 1920 x 1080, while dual link cables can achieve a resolution of 2048 x 1536. So, check your LCD specs, if it says single link, then there is no point in getting a dual link cable (not quite true, since you can use a dual link cable later if you upgrade your LCD). The price difference between a single link an dual link cable is usually only a few bucks.

    DVI-A - Analog

    DVI-A format is used to carry a DVI signal to an analog display, such as a CRT monitor or an HDTV with a traditional VGA (HD15) connector. The DVI connector has reserved pins for the old analog RBG signals, given the fact that your DVI video card outputs these analog signals (check with your card mfg) the DVI-A cable is used to carry these RGB (and sync) signals to your display.

    DVI-I - Integrated Digital and Analog

    Although we have not listed any DVI-I cables in the above table, HRT can provide this type of DVI cable upon request. DVI-I cables are used for transmitting either a digital-to-digital signal or an analog-to-analog signal, in fact it has a DVI connector on both ends and can be used in place of a DVI-D cable. It will not work for transmitting a digital-to-analog or vice versa. Some LCD's DVI inputs are purely digital and some may be labeled 'DVI-I' which means that the LCD can accept both DVI-D and DVI-A source signals.

    HOW DO I DETERMINE WHAT KIND OF DVI FORMAT MY LCD OR VIDEO CARD SUPPORT?

    You have to check your documentation that comes with the equipment. Most video cards output DVI-I format which means that you can connect them to a purely DVI-D, or DVI-A, or even VGA LCD. The trend for LCD's is that they are mostly DVI-D. That explains why DVI-D cables sell the most.

    But to help you try to identify the type, first locate the flat horizontal 'blade looking' pin to one side of the connector. This can help tell you if you are dealing with digital or analog. A flat pin with four surrounding pins is either DVI-I or DVI-A, while a flat pin alone denotes DVI-D.

    The rest of the pins tell you if you are dealing with single- or dual-link. A solid 27-pin set (rows of 8) usually means dual-link, while two separated 9-pin sets (rows of 6) identifies a single-link cable.

    One more thing, if you have a flat pin with four surrounding pins, then a solid 27-pin set indicates a DVI-I, while separated 8-pin and 4-pin sets means DVI-A.

    This site has piccies too http://www.ramelectronics.net/html/DVI_monitor_cables.html#vid-card
     
  2. dean randle

    dean randle
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  3. Gavin_Hall

    Gavin_Hall
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    Excellent information, thanks :lesson: .

    I hope a mod makes this sticky! :smashin:
     

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