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naling) protocol that Silicon Image developed. Unfortunately, both of these interfaces had
relatively low-resolution support (1280×1024 maximum) and were only implemented in
a handful of video cards and monitors. As such, they never really caught on in the mass
market and were overshadowed by the DVI, which become the first truly popular digital
display interface standard.
DVI
DVI was introduced on April 2, 1999 by the Digital Display Working Group (DDWG).
TheDDWGwasformedin1998byIntel,SiliconImage,Compaq,Fujitsu,Hewlett-Pack-
ard, IBM, and NEC to address the need for a universal digital interface standard between
a host system and a display. Unlike the P&D and DFP interfaces that came before it, DVI
gainedimmediatewidespreadindustrysupport,with150DVIproductsbeingshownatthe
Intel Developer Forum in August 1999, only four months after DVI was released. Since
then, DVI has become the most popular interface for digital video connections. DVI also
allows for both digital and VGA analog connections using the same basic connector.
DVI uses Transition Minimized Differential Signaling (TMDS), which was developed
by Silicon Image ( www.siliconimage.com ) and trademarked under the name PanelLink .
TMDS takes 24-bit parallel digital data from the video controller and transmits it serially
overbalancedlinesatahighspeedtoareceiver.Asingle-linkTMDSconnectionusesfour
separate differential data pairs, with three for color data (one each for red, green, and blue
data)andthefourthpairforclockandcontroldata.Eachtwisted pairusesdifferential sig-
nalingwithalow0.5Vswingoverbalancedlinesforreliable,low-power,high-speeddata
transmission. A low-speed VESA Display Data Channel (DDC) pair is also used to trans-
mit identification and configuration information, such as supported resolution and color-
depth information, between the graphics controller and display.
TMDS is designed to support cables up to 10 meters (32.8 feet) in length, although the
limits may be shorter or longer depending on cable quality. Several companies make
products that can amplify or re-drive the signals, allowing for greater lengths. Figure 12.4
shows a block diagram of a single-link TMDS connection.
Figure 12.4 A single-link TMDS connection.
 
 
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