AKLUG Archive: [aklug] DVI Standard Information

From: Piet van Weel <pmvw@outwardfocus.net>
Date: Thu Jan 24 2008 - 10:54:29 AKST

Hey Guys...
I've been dealing with DVI issues here at KTUU, so I figured I would post
this to the group in case someone else was dealing with similar issues. The
information was taken from www.datapro.net[1]

Piet

All About DVI A Complete Guide to the Digital Video Interface

[IMG]

  * What is DVI?[2]
  * What are the DVI Formats?[3]
  * What are single and dual links?[4]
  * How far does DVI go?[5]
  * How do I know which cable to use?[6]
  * How to recognize a DVI Cable[7]
  * List of DataPro DVI Products[8]
Still not sure what DVI cable you need?
Find out![9]
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WHAT IS DVI ? DVI stands for (D)igital (V)ideo (I)nterface.

DVI is a popular form of video interface technology made to maximize the
quality of flat panel LCD monitors and modern 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 cables are becoming
increasingly popular with video card manufacturers, and most cards nowadays
include both a VGA and a DVI output port.

In addition to being used as the standard computer interface, the DVI
standard was, for a short while, 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 top-end DVD players have featured DVI
outputs in addition to the high-quality analog Component Video. The digital
market is now swinging towards the HDMI interface[10] for high-definition
media delivery, and DVI is being again constrained to the computer market.
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WH
AT ARE THE DVI FORMATS ? There are three types of DVI connections:
DVI-Digital, DVI-Analog, and DVI-Integrated (Digital &Analog)

DVI-D - True Digital Video DVI-D cables[11] are 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 cables[12] are used to carry a DVI signal to an analog display, such
asa CRT monitor or budget LCD. The most common use of DVI-A is connecting to
a VGA device, since DVI-A and VGA carry the same signal. There is some
quality loss involved in the digital to analog conversion, which is why a
digital signal is recommended whenever possible. DVI-I - The Best of Both
Worlds DVI-I cables[13] are integrated cables which are capable of
transmitting either a digital-to-digital signal or an analog-to-analog
signal. This makes it a more versatile cable, being usable in either digital
or analog situations. 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. To connect an analog source
to a digital display, you'll need a VGA to DVI-D electronic convertor[14];
toconnect a digital output to an analog monitor, you'll need to use a DVI-D
to VGA convertor[15].
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WHAT ARE SINGLE AND DUAL LINKS ? The Digital formats
are available in DVI-D Single-Link[16] and Dual-Link[17] as well as DVI-I
Single-Link and Dual-Link[18] format connectors. These DVI 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 DVI pins effectively
double the power of transmission and provide an increase of speed and signal
quality; i.e. a DVI single link 60-Hz LCD can display a resolution of 1920 x
1080, while a DVI dual link can display a resolution of 2048 x 1536.
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HOW FAR
IS THE DVI MAXIMUM LENGTH? The official DVI specification mandates that all
DVI equipment must maintain a signal at 5 meters (16 feet) in length. But
many manufacturers are putting out much stronger cards and bigger monitors,
so the maximum length possible is never exact.

Although the mandated DVI spec is 5 meters, we do carry cables up to 25
feet,and have succesfully extended them even longer than that (although
results do vary depending on hardware). For guaranteed signal quality on
longruns, you should consider using a powered DVI signal booster[19].

Despite common belief, there is such thing as signal loss in digital
pictures. When a DVI run is unstable, you may see artifacts and "stuck"
pixels on your display; further degredation tends to flicker out or shake,
and the ultimate sign of loss is a blank display. In-house tests on varying
equipment have produced strong signals up to 9 and 10 meters long. Tests at
12 meters generally resulted in signal loss and an unusuable image on the
display, and anything longer rendered no image at all.

Keep in mind that when using DVI-I cables at extensive lengths, you may not
be seeing a digitally-clear image on your screen. Because analog has a much
longer run, your display may auto-switch once the digital signal is too
weak.For this reason, long runs are best done with VGA (for analog) or HDMI
(for digital). If you have no option other than DVI, make sure you're
gettingthe best image by using DVI-D cables and verifing that your display
isset to digital input.
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HOW DO I KNOW WHICH CABLE TO USE? Determining which
type of DVI cable to use for your products is critical in getting the right
cable the first time. Check both of the female DVI plugs to determine what
signals they are compatible with.
  * If one or both connections are DVI-D, you need a DVI-D cable[20].
  * If one or both connections are DVI-A, you need a DVI-A cable[21].
  * If one connection is DVI and the other is VGA, and the DVI is
analog-compatible, you need a DVI to VGA cable[22] or a DVI/VGA adaptor[23].

* If both connections are DVI-I, you may use any DVI cable, but a DVI-I
cable[24] is recommended.
* If one connection is analog and the other connection is digital, there
isno way to connect them with a single cable. You'll have to use an
electronic convertor box, available in either analog VGA to digital DVI[25]
or digital DVI to analog VGA[26].
If you still have questions, look at our DVI cable guide[27] for an
easy-to-use chart to help you find the right cable for you.
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HOW TO RECOGNIZE
A DVI CABLE There are two variables in every DVI connector, 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 the cable is single-link, dual-link,
oranalog:
  * Two separated 9-pin sets (rows of 6) for a single-link cable
  * A solid 24-pin set (rows of 8) for a dual-link cable
  * A separated 8-pin and 4-pin set is for DVI-A.
DVI Connector Guide DVI-D Single Link DVI-A DVI-I Single Link Digital Only
Analog Only Digital &Analog Two sets of nine pins, and a
solitary flat blade One set of eight pins and one set of four pins, with
fourcontacts around the blade Two sets of nine pins and four contacts around
the blade DVI-D Dual Link
DVI-I Dual Link Digital Only
Digital &Analog [IMG]
Three rows of eight pins and a solitary flat blade
Three rows of eight pins and four contacts around the blade
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Received on Thu Jan 24 10:55:11 2008

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