Tuesday, December 4, 2007

A male DVI-I (dual link) connector A male DVI-I (dual link) connector.
The Digital Visual Interface (DVI) is a video interface standard designed to maximize the visual quality of digital display devices such as flat panel LCD computer displays and digital projectors. It was developed by an industry consortium, the Digital Display Working Group (DDWG). It is designed for carrying uncompressed digital video data to a display. It is partially compatible with the High-Definition Multimedia Interface (HDMI) standard in digital mode (DVI-D).

The data format used by DVI is based on the PanelLink serial format devised by the semiconductor manufacturer Silicon Image Inc. This uses Transition Minimized Differential Signaling (TMDS). A single DVI link consists of four twisted pairs of wire (red, green, blue, and clock) to transmit 24 bits per pixel. The timing of the signal almost exactly matches that of an analog video signal. The picture is transmitted line by line with blanking intervals between each line and each frame, and without packetization. No compression is used and there is no support for only transmitting changed parts of the image. This means that the whole frame is constantly re-transmitted. The specification (see below for link) does, however, include a paragraph on "Conversion to Selective Refresh" (under 1.2.2), suggesting this feature for future devices.
With a single DVI link, the largest resolution possible at 60 Hz is 2.75 megapixels (including blanking interval). For practical purposes, this allows a maximum screen resolution at 60 Hz of 1915 x 1436 pixels (standard 1.33 ratio), 1854 x 1483 pixels (1.25 ratio) or 2098 x 1311 (widescreen 1.6 ratio). The DVI connector therefore has provision for a second link, containing another set of red, green, and blue twisted pairs. When more bandwidth is required than is possible with a single link, the second link is enabled, and alternate pixels may be transmitted on each, allowing resolutions up to 4 megapixels at 60 Hz. The DVI specification mandates a fixed single link maximum pixel clock frequency of 165 MHz, where all display modes that require less than this must use single link mode, and all those that require more must switch to dual link mode. When both links are in use, the pixel rate on each may exceed 165 MHz. The second link can also be used when more than 24 bits per pixel is required, in which case it carries the least significant bits. The data pairs carry binary data at ten times the pixel clock reference frequency, maximum 1.65 Gbit/s x 3 data pairs for a single DVI link.
Like modern analog VGA connectors, the DVI connector includes pins for the display data channel. DDC2 (a newer version of DDC) 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 input, each input can host a distinct EDID. If both receivers are active, analog EDID is used.
There is a length limitation of 15-foot (4.6m) in DVI cables. For longer distances, to eliminate the video degradation, the use of a DVI booster is recommended. DVI boosters may or may not use an external power supply.

Technical discussion
In Radeon HD, audio signals are carried through DVI when the video card detects a connected HDMI display, which is connected via the HDMI adapter which is optionally supplied by the manufacturer (it appears that the 2400 Pro models do not come with the required adaptor).[1]

The DVI connector usually contains pins to pass the DVI-native digital video signals. In the case of dual-link systems, additional pins are provided for the second set of data signals.
As well as digital signals, the DVI connector includes pins providing the same analog signals found on a VGA connector, allowing a VGA monitor to be connected with a simple plug adapter. This feature was included in order to make DVI universal, as it allows either type of monitor (analog or digital) to be operated from the same connector.
The DVI connector on a device is therefore given one of three names, depending on which signals it implements:
The connector also includes provision for a second data link for high resolution displays, though many devices do not implement this. In those that do, the connector is sometimes referred to as DVI-DL (dual link).
The long flat pin on a DVI-I connector is longer than the same pin on a DVI-D connector, so it is not possible to connect a male DVI-I to a female DVI-D by removing the 4 analog pins. It is possible, however, to connect a male DVI-D cable to a female DVI-I connector. Many flat screen LCD monitors have only the DVI-D connection so that a DVI-D male to DVI-D male cable will suffice when connecting the monitor to a computer's DVI-I female connector.
DVI is the only widespread video standard that includes analog and digital transmission options in the same connector. Competing standards are exclusively digital: these include a system using low-voltage differential signaling (LVDS), known by its proprietary names FPD (for Flat-Panel Display) Link and FLATLINK; and its successors, the LVDS Display Interface (LDI) and OpenLDI.
Some new DVD players, TV sets (including HDTV sets) and video projectors have DVI/HDCP connectors; these are physically the same as DVI connectors but transmit an encrypted signal using the HDCP protocol for copy protection. Computers with DVI video connectors can use many DVI-equipped HDTV sets as a display; however, due to Digital Rights Management, it is not clear whether such systems will eventually be able to play protected content, as the link is not encrypted.
USB signals are not incorporated into the connector, but were earlier incorporated into the VESA Plug and Display connector used by InFocus on their projector systems, and in the Apple Display Connector, which was used by Apple Computer until 2005.

DVI-D (digital only)
DVI-A (analog only)
DVI-I (digital & analog) Specifications
GTF (General Timing Formula) is a VESA standard which can easily be calculated with the Linux gtf utility.

Minimum clock frequency: 21.76 MHz
Maximum clock frequency in single link mode: Capped at 165 MHz (3.7 Gbit/s)
Maximum clock frequency in dual link mode: Limited only by cable quality (more than 7.4 Gbit/s)
Pixels per clock cycle: 1 (single link) or 2 (dual link)
Bits per pixel: 24
Example display modes (single link):

  • HDTV (1920 × 1080) @ 60 Hz with 5% LCD blanking (131 MHz)
    UXGA (1600 × 1200) @ 60 Hz with GTF blanking (161 MHz)
    WUXGA (1920 × 1200) @ 60 Hz (154 MHz)
    SXGA (1280 × 1024) @ 85 Hz with GTF blanking (159 MHz)
    WXGA+ (1440 x 900) @ 60 Hz (107 MHz)
    WQUXGA (3840 × 2400) @ 17 Hz (164 MHz)
    Example display modes (dual link):

    • QXGA (2048 × 1536) @ 75 Hz with GTF blanking (2×170 MHz)
      HDTV (1920 × 1080) @ 85 Hz with GTF blanking (2×126 MHz)
      WQXGA (2560 × 1600) @ 60 Hz with GTF blanking (2x174 MHz) (30" Apple, Dell, HP, Quinux, and Samsung LCDs)
      WQUXGA (3840 × 2400) @ 33 Hz with GTF blanking (2x159 MHz) Analog

      ADC – Apple Display Connector, a similar, now-obsolete connector that can still be found on some older Macs. Based on DVI, with USB and power capabilities included.
      VGA connector, analog video (an older standard, though very common on current computer hardware)
      High-Definition Multimedia Interface (HDMI), a forward-compatible standard, that also includes digital audio transmission
      Unified Display Interface (UDI), a proposed future standard to replace both DVI and HDMI
      DisplayPort, another proposed standard, incompatible with DVI and HDMI
      DMS-59, a way to combine 2 analog and 2 digital signals in one connector. Commonly used to give 2 x DVI outputs from one graphics card connector.
      DFP, an older type of digital video link
      M1-DA, a proprietary plug used in some projectors and sometimes labeled as DVI-M1
      LCD TV
      List of display interfaces

No comments: