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Digital Visual Interface

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The Digital Visual Interface, commonly known as DVI, is a video display interface. It was created to connect a video source to a display device. A video source is often a video display controller. The display device is usually a computer monitor.

DVI Logo
DVI Logo

The Digital Display Working Group (DDWG) developed DVI. Their goal was to create an industry standard for transferring uncompressed digital video content. This means the video data is not squeezed or changed during the transfer. This high level of fidelity ensures the image remains clear. While DVI is mostly used for computers, it also appears in other electronics. You might find DVI ports on television sets or DVD players.

DVI uses a specific method to move data called transition minimized differential signaling, or TMDS.

DVI Connector Pinout
DVI Connector Pinout

This is a high-speed serial link. TMDS transports digital video pixel data using multiple twisted pairs of wires. These twisted pairs are very important for signal quality. They are highly resistant to electrical noise and other forms of analog distortion. This helps keep the digital signal clean as it moves from the source to the screen. The system does not use packetization. Instead, it transmits pixel data as if it were a rasterized analog video signal. This means a complete frame is drawn during each vertical refresh period.

There are different ways a DVI connection can be configured. A single link DVI connection uses four TMDS pairs. Three of these data pairs carry the 8-bit RGB components. These represent the red, green, and blue parts of the video signal. Together, these three pairs provide 24 bits per pixel. The fourth pair carries the TMDS clock to keep the timing correct. Single link mode has a maximum TMDS clock frequency of 165 MHz. This supports a maximum resolution of 2.75 megapixels at 60 Hz. For most users, this means a maximum resolution of 1920 × 1200 at 60 Hz.

DVI pinout no info
DVI pinout no info

To support higher-resolution devices, the DVI specification includes a dual link option. Dual link DVI doubles the number of TMDS data pairs. This effectively doubles the available video bandwidth. This extra capacity allows for much higher resolutions. Dual link can support resolutions up to 2560 × 1600 at 60 Hz. It can also support higher refresh rates for lower resolutions. Dual link DVI adds six pins at the center of the connector. These extra pins allow for a second transmitter. Some people call these connectors DVI-DL. It is important not to confuse dual link with dual display. Dual display refers to connecting one computer to two separate monitors.

DVI connectors are categorized by the types of signals they carry. There are three main types: DVI-I, DVI-D, and DVI-A. DVI-I stands for integrated. These connectors combine both digital and analog signals in one plug. They include VGA pins for analog compatibility. DVI-D is digital only. It can be either single link or dual link. DVI-A is analog only.

Adapter DVI to VGA
Adapter DVI to VGA

Most DVI connectors, except for DVI-A, carry digital video signals. Because DVI-I carries analog signals, it is compatible with the analog VGA interface. You can use a simple, cheap passive adapter to connect a VGA monitor to a DVI-I source. However, a DVI-D output requires a more expensive active adapter to work with VGA.

The history of DVI involves several competing standards. In 1994 and 1995, VESA created the Enhanced Video Connector, or EVC. The EVC used a 35-pin Molex MicroCross connector. It carried analog video, analog stereo audio, and data via USB or FireWire. Later, VESA released the Plug & Display (P&D) standard in 1997. P&D used the same 35-pin connector but focused on digital video. A different group developed the Digital Flat Panel (DFP) standard in 1999. DFP used a 20-pin micro ribbon connector and only sent digital video. DVI succeeded because it could support dual-link TMDS signals. This allowed for higher resolutions than P&D or DFP. DVI began appearing in products in 1999. One of the first DVI monitors was the Apple Cinema Display.

DVI also includes a smart communication system called the display data channel, or DDC.

DVI pinout no info
DVI pinout no info

The DDC allows the graphics adapter to read the monitor's extended display identification data, known as EDID. When you connect a source and a display, the source queries the display's capabilities. It reads the EDID block over an I²C link. This block contains the monitor's identification and its color characteristics, like its gamma value. It also contains a table of supported video modes. Each mode tells the computer the resolution, the refresh rate, and the timing values. This ensures the computer and the monitor can work together perfectly.

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File:DVI_Logo.svg
DVI_Logo.svg
File:DVI Connector Pinout.svg
DVI Connector Pinout.svg
File:DVI pinout no info.png
DVI pinout no info.png
File:Adapter DVI to VGA.jpg
Adapter DVI to VGA.jpg
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