Digital Visual Interface

Digital Visual Interface (DVI)
DVI.png
TypeDigital computer video connector
DesignerDigital Display Working Group
DesignedApril 1999
Produced1999–present
SupersededVGA connector
Superseded byDisplayPort, HDMI
Hot pluggableYes
ExternalYes
Video signalDigital video stream:
Single link: 1920 × 1200 (WUXGA) @ 60 Hz
Dual link: 2560 × 1600 (WQXGA) @ 60 Hz
Analog video stream: 1920 × 1200 (WUXGA) @ 60 Hz
Pins29
Data signalRGB data, clock, and display data channel
Bitrate(Single link) 3.96 Gbit/s
(Dual link) 7.92 Gbit/s
Max. devices1
Protocol3 × transition minimized differential signaling data and clock
DVI Connector Pinout.svg
A female DVI-I socket from the front
DVI pinout.svg
Color coded (click to read text)
Pin 1TMDS data 2−Digital red− (link 1)
Pin 2TMDS data 2+Digital red+ (link 1)
Pin 3TMDS data 2/4 shield
Pin 4TMDS data 4−Digital green− (link 2)
Pin 5TMDS data 4+Digital green+ (link 2)
Pin 6DDC clock
Pin 7DDC data
Pin 8Analog vertical sync
Pin 9TMDS data 1−Digital green− (link 1)
Pin 10TMDS data 1+Digital green+ (link 1)
Pin 11TMDS data 1/3 shield
Pin 12TMDS data 3−Digital blue− (link 2)
Pin 13TMDS data 3+Digital blue+ (link 2)
Pin 14+5 VPower for monitor when in standby
Pin 15GroundReturn for pin 14 and analog sync
Pin 16Hot plug detect
Pin 17TMDS data 0−Digital blue− (link 1) and digital sync
Pin 18TMDS data 0+Digital blue+ (link 1) and digital sync
Pin 19TMDS data 0/5 shield
Pin 20TMDS data 5−Digital red− (link 2)
Pin 21TMDS data 5+Digital red+ (link 2)
Pin 22TMDS clock shield
Pin 23TMDS clock+Digital clock+ (links 1 and 2)
Pin 24TMDS clock−Digital clock− (links 1 and 2)
C1Analog red 
C2Analog green 
C3Analog blue 
C4Analog horizontal sync 
C5Analog groundReturn for R, G, and B signals

Digital Visual Interface (DVI) is a video display interface developed by the Digital Display Working Group (DDWG). The digital interface is used to connect a video source, such as a video display controller, to a display device, such as a computer monitor. It was developed with the intention of creating an industry standard for the transfer of digital video content.

The interface is designed to transmit uncompressed digital video and can be configured to support multiple modes such as DVI-A (analog only), DVI-D (digital only) or DVI-I (digital and analog). Featuring support for analog connections, the DVI specification is compatible with the VGA interface.[1] This compatibility, along with other advantages, led to its widespread acceptance over competing digital display standards Plug and Display (P&D) and Digital Flat Panel (DFP).[2] Although DVI is predominantly associated with computers, it is sometimes used in other consumer electronics such as television sets and DVD players.

Technical overview

DVI's digital video transmission format is based on panelLink, a serial format developed by Silicon Image that utilizes a high-speed serial link called transition minimized differential signaling (TMDS). Like modern analog VGA connectors, the DVI connector includes pins for the display data channel (DDC). A newer version of DDC called DDC2 allows the graphics adapter to read the monitor's extended display identification data (EDID). If a display supports both analog and digital signals in one DVI-I input, each input method can host a distinct EDID. Since the DDC can only support one EDID, this can be a problem if both the digital and analog inputs in the DVI-I port detect activity. It is up to the display to choose which EDID to send.

When a source and display are connected, the source first queries the display's capabilities by reading the monitor EDID block over an I²C link. The EDID block contains the display's identification, color characteristics (such as gamma level), and table of supported video modes. The table can designate a preferred mode or native resolution. Each mode is a set of CRT timing values that define the duration and frequency of the horizontal/vertical sync, the positioning of the active display area, the horizontal resolution, vertical resolution, and refresh rate.

For backward compatibility with displays using analog VGA signals, some of the contacts in the DVI connector carry the analog VGA signals. To ensure a basic level of interoperability, DVI compliant devices are required to support one baseline video mode, "low pixel format" (640 × 480 at 60 Hz). Digitally encoded video pixel data is transported using multiple TMDS links. At the electrical level, these links are highly resistant to electrical noise and other forms of analog distortion.

A single link DVI connection consists of four TMDS links; each link transmits data from the source to the device over one twisted wire pair. Three of the links represent the RGB components (red, green, and blue) of the video signal for a total of 24 bits per pixel. The fourth link carries the pixel clock. The binary data is encoded using 8b10b encoding. DVI does not use packetization, but rather transmits the pixel data as if it were a rasterized analog video signal. As such, the complete frame is drawn during each vertical refresh period. The full active area of each frame is always transmitted without compression. Video modes typically use horizontal and vertical refresh timings that are compatible with CRT displays, though this is not a requirement. In single-link mode, the maximum pixel clock frequency is 165 MHz that supports a maximum resolution of 2.75 megapixels (including blanking interval) at 60 Hz refresh. For practical purposes, this allows a maximum 16:10 screen resolution of 1920 × 1200 at 60 Hz.

To support higher-resolution display devices, the DVI specification contains a provision for dual link. Dual-link DVI doubles the number of TMDS pairs, effectively doubling the video bandwidth. As a result, higher resolutions up to 2560 × 1600 are supported at 60 Hz.

Cable length

The maximum length recommended for DVI cables is not included in the specification, since it is dependent on the pixel clock frequency. In general, cable lengths up to 4.5 metres (15 ft) will work for display resolutions up to 1920 × 1200. Longer cables up to 15 metres (49 ft) in length can be used with display resolutions 1280 × 1024 or lower. For greater distances, the use of a DVI booster—a signal repeater which may use an external power supply—is recommended to help mitigate signal degradation.

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