VGA connector

Last updated
VGA connector (DE-15/HD-15)
SVGA port.jpg
A female DE-15 output in a laptop computer
Type Computer analog video connector
Designer IBM based on D-subminiature
Designed 1987
Produced 1987–present
Superseded by DVI (1999)
Hot pluggable Depends
Video signal RGB video signal plus option H and V sync
Pins 15
Connector DE-15
Data signal I²C data channel for DDC information
VGA Port.svg
A female DE15 socket
Pin 1 RED Red video
Pin 2 GREEN Green video
Pin 3 BLUE Blue video
Pin 4 ID2/RES Reserved since E-DDC, formerly monitor id. bit 2
Pin 5 GND Ground (HSync)
Pin 6 RED_RTN Red return
Pin 7 GREEN_RTN Green return
Pin 8 BLUE_RTN Blue return
Pin 9 KEY/PWR +5 V DC (powers EDID EEPROM chip on some monitors), formerly key
Pin 10 GND Ground (VSync, DDC)
Pin 11 ID0/RES Reserved since E-DDC, formerly monitor id. bit 0
Pin 12 ID1/SDA I²C data since DDC2, formerly monitor id. bit 1
Pin 13 HSync Horizontal sync
Pin 14 VSync Vertical sync
Pin 15 ID3/SCL I²C clock since DDC2, formerly monitor id. bit 3
The image and table detail the 15-pin VESA DDC2/E-DDC connector; the diagram’s pin numbering is that of a female connector functioning as the graphics adapter output. In the male connector, this pin numbering corresponds with the cable's wire-and-solder side.

The Video Graphics Array (VGA) connector is a standard connector used for computer video output. Originating with the 1987 IBM PS/2 and its VGA graphics system, the 15-pin connector went on to become ubiquitous on PCs, [1] as well as many monitors, projectors and high definition television sets.

Contents

Other connectors have been used to carry VGA-compatible signals, such as mini-VGA or BNC, but "VGA connector" typically refers to this design. [2]

Devices continue to be manufactured with VGA connectors, although newer digital interfaces such as DVI, HDMI and DisplayPort are increasingly displacing VGA, and many modern computers and other devices do not include it. [3]

Physical design

The VGA connector is a three-row, 15-pin D-subminiature connector referred to variously as DE-15, [2] HD-15 [4] or DB-15. DE-15 is the most accurate common nomenclature under the D-sub specifications: an "E" size D-sub connector, with 15 pins in three rows.

Electrical design

All VGA connectors carry analog RGBHV (red, green, blue, horizontal sync, vertical sync) video signals. Modern connectors also include VESA DDC pins, for identifying attached display devices.

In both its modern and original variants, VGA utilizes multiple scan rates, so attached devices such as monitors are multisync by necessity.

The VGA interface includes no affordances for hot swapping, the ability to connect or disconnect the output device during operation, although in practice this can be done and usually does not cause damage to the hardware or other problems. The VESA DDC specification does however include a standard for hot-swapping. [5]

PS/2 signaling

In the original IBM VGA implementation, refresh rates were limited to two vertical (60 and 70 Hz) and three horizontal frequencies, all of which were communicated to the monitor using combinations of different polarity H and V sync signals. [6] :100

Some pins on the connector were also different: pin 9 was keyed by plugging the female connector hole, and four pins carried the monitor ID. [6] :99

With the implementation of the VESA DDC specification, several of the monitor ID pins were reassigned for use by DDC signaling, and the key pin was replaced with a +5 V DC output per the DDC spec. Devices that comply with the DDC host system standard provide 5 V ± 5%, from 50 mA to 1 A. [7]

PS/55 signaling

The IBM PS/55 Display Adapter redefined pin 9 as "+12V", [8] which signals the monitor to turn on when the system unit is powered on. [9]

Cable quality

A VGA cable with DE-15 male connector Vga-cable.jpg
A VGA cable with DE-15 male connector

The same VGA cable can be used with a variety of supported VGA resolutions, ranging from 320×400px @70 Hz, or 320×480px @60 Hz (12.6 MHz of signal bandwidth) to 1280×1024px (SXGA) @85 Hz (160 MHz) and up to 2048×1536px (QXGA) @85 Hz (388 MHz).

There are no standards defining the quality required for each resolution, but higher-quality cables typically contain coaxial wiring and insulation that make them thicker.

While shorter VGA cables are less likely to introduce significant signal degradation, good-quality cable should not suffer from signal crosstalk (whereby signals in one wire induce unwanted currents in adjacent wires) even at greater lengths.

Ghosting occurs when impedance mismatches cause signals to be reflected. A correctly impedance matched cable (75 ohm) should prevent this, however, ghosting with long cables may be caused by equipment with incorrect signal termination or by passive cable splitters rather than the cables themselves.

Alternative connectors

VGA BNC connectors BNC connectors.jpg
VGA BNC connectors

Some high-end monitors and video cards use multiple BNC connectors instead of a single standard VGA connector[ which? ], providing a higher quality connection with less crosstalk[ according to whom? ] by utilizing five separate 75 ohm coaxial cables.

Within a 15-pin connector, the red, green, and blue signals (pins 1, 2, 3) cannot be shielded from each other, so crosstalk is possible within the 15-pin interconnect. BNC prevents crosstalk by maintaining full coaxial shielding through the circular connectors, but the connectors are very large and bulky. The requirement to press and turn the plug shell to disconnect requires access space around each connector to allow grasping of each BNC plug shell. Supplementary signals such as DDC are typically not supported with BNC.

Mini-VGA port on a Mac laptop Mini-VGA cropped.jpg
Mini-VGA port on a Mac laptop

Some laptops and other small devices[ which? ] use a two-row mini-VGA connector that is much smaller than the three-row DE-15 connector, as well as five separate BNC connectors.

Adapters

Various adapters can be purchased to convert VGA to other connector types. One common variety is a DVI to VGA adapter, which is possible because many DVI interfaces also carry VGA-compatible analog signals. Adapting from HDMI to VGA directly is not possible because HDMI includes no analog signal.

For conversions to and from digital formats like HDMI or DVI-D, a scan converter is required. VGA outputs to interfaces with different signaling, more complex converters may be used. Most of them need an external power source to operate and are inherently lossy. However, many modern displays are still made with multiple inputs including VGA, in which case adapters are not necessary.

VGA can also be adapted to SCART in some cases, because the signals are electrically compatible if the correct sync rates are set by the host PC. Many modern graphics adapters can modify their signal in software, including refresh rate, sync length, polarity and number of blank lines. Particular issues include interlace support and the use of the resolution 720×576 in PAL countries. Under these restrictive conditions, a simple circuit to combine the VGA separate synchronization signals into SCART composite sync may suffice. [10] [11]

Extenders

A VGA Extender is an electronic device that increases the signal strength from a VGA port, most often from a computer. They are often used in schools, businesses, and homes when multiple monitors are being run off one VGA port, or if the cable between the monitor and the computer will be excessively long (often pictures appear blurry or have minor artifacts if the cable runs too far without an extender). VGA extenders are sometimes called VGA boosters.

See also

Related Research Articles

Digital Visual Interface Standard for transmitting digital video to a display

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.

VESA, formally known as Video Electronics Standards Association, is an American technical standards organization for computer display standards. The organization was incorporated in California in July 1989 and has its office in San Jose. It claims a membership of over 300 companies.

Video Graphics Array Computer display standard and resolution

Video Graphics Array (VGA) is a video display controller and accompanying de facto graphics standard, first introduced with the IBM PS/2 line of computers in 1987, which became ubiquitous in the PC industry within three years. The term can now refer to the computer display standard, the 15-pin D-subminiature VGA connector, or the 640×480 resolution characteristic of the VGA hardware.

SCART 21-pin connector for audio-visual equipment

SCART is a French-originated standard and associated 21-pin connector for connecting audio-visual (AV) equipment. The name SCART comes from Syndicat des Constructeurs d'Appareils Radiorécepteurs et Téléviseurs, "Radio and Television Receiver Manufacturers' Association", the French organisation that created the connector in the mid-1970s. The related European standard EN 50049 has been then refined and published in 1978 by CENELEC, calling it péritelevision, but it is commonly called by the abbreviation péritel in French.

Graphics card Expansion card which generates a feed of output images to a display device

A graphics card is an expansion card which generates a feed of output images to a display device. Frequently, these are advertised as discrete or dedicated graphics cards, emphasizing the distinction between these and integrated graphics. At the core of both is the graphics processing unit (GPU), which is the main part that does the actual computations, but should not be confused with the graphics card as a whole, although "GPU" is often used as a metonymic shorthand to refer to graphics cards.

S-Video signaling standard for SD video

S-Video is a signaling standard for standard definition video, typically 480i or 576i. By separating the black-and-white and coloring signals, it achieves better image quality than composite video, but has lower color resolution than component video. S-Video was introduced with JVC's S-VHS format in 1987.

Component video Video signal that has been split into component channels

Component video is an analog video signal that has been split into two or more component channels. In popular use, it refers to a type of component analog video (CAV) information that is transmitted or stored as three separate signals. Component video can be contrasted with composite video in which all the video information is combined into a single signal that is used in analog television. Like composite, component-video cables do not carry audio and are often paired with audio cables.

The Display Data Channel, or DDC, is a collection of protocols for digital communication between a computer display and a graphics adapter that enable the display to communicate its supported display modes to the adapter and that enable the computer host to adjust monitor parameters, such as brightness and contrast.

HDMI Proprietary interface for transmitting digital audio and video data

High-Definition Multimedia Interface (HDMI) is a proprietary audio/video interface for transmitting uncompressed video data and compressed or uncompressed digital audio data from an HDMI-compliant source device, such as a display controller, to a compatible computer monitor, video projector, digital television, or digital audio device. HDMI is a digital replacement for analog video standards.

Composite monitor

A composite monitor or composite video monitor is any analog video display that receives input in the form of an analog composite video signal to a defined specification. A composite video signal encodes all information on a single conductor; a composite cable has a single live conductor plus earth. Other equipment with display functionality includes monitors with more advanced interfaces and connectors giving a better picture, including analog VGA, and digital DVI, HDMI, and DisplayPort; and television (TV) receivers which are self-contained, receiving and displaying video RF broadcasts received with an internal tuner. Video monitors are used for displaying computer output, closed-circuit television and other applications requiring a two-dimensional monochrome or colour image.

DB13W3

DB13W3 (13W3) is a style of D-subminiature connector commonly used for analog video interfaces. The 13 refers to the total number of pins, the W refers to workstation and the 3 refers to the number of high-frequency pins.

DisplayPort Digital display interface

DisplayPort (DP) is a digital display interface developed by a consortium of PC and chip manufacturers and standardized by the Video Electronics Standards Association (VESA). The interface is primarily used to connect a video source to a display device such as a computer monitor, and it can also carry audio, USB, and other forms of data.

DMS-59

DMS-59 was generally used for computer video cards. It provides two Digital Visual Interface (DVI) or Video Graphics Array (VGA) outputs in a single connector. A Y-style breakout cable is needed for the transition from the DMS-59 output to DVI (digital) or VGA (analogue), and different types of adapter cables exist. The connector is four pins high and 15 pins wide, with a single pin missing from the bottom row, in a D-shaped shell, with thumbscrews. As of December 2020, this adapter cable was listed as obsolete by its primary vendor Molex.

Mini-DVI

The Mini-DVI connector is used on certain Apple computers as a digital alternative to the Mini-VGA connector. Its size is between the full-sized DVI and the tiny Micro-DVI. It is found on the 12-inch PowerBook G4, the Intel-based iMac, the MacBook Intel-based laptop, the Intel-based Xserve, the 2009 Mac mini, and some late model eMacs.

Dreamcast VGA

The Dreamcast VGA Box is an accessory for Sega's Dreamcast video game console that allows it to connect to a video display such as a computer monitor or a HDTV set through a VGA port. Because the Dreamcast hardware can produce a VGA-compatible video signal natively, this connection provides improved picture quality compared to standard composite video or S-Video connections, along with support for progressive scan video.

Mobile High-Definition Link (MHL) is an industry standard for a mobile audio/video interface that allows the connection of smartphones, tablets, and other portable consumer electronics devices to high-definition televisions (HDTVs), audio receivers, and projectors. The standard was designed to share existing mobile device connectors, such as Micro-USB, and avoid the need to add additional video connectors on devices with limited space for them.

Mini DisplayPort

The Mini DisplayPort is a miniaturized and less common version of the DisplayPort audio-visual digital interface.

Audio connectors and video connectors are electrical or optical connectors for carrying audio and video signals. Audio interfaces and video interfaces define physical parameters and interpretation of signals. For digital audio and digital video, this can be thought of as defining the physical layer, data link layer, and most or all of the application layer. For analog audio and analog video these functions are all represented in a single signal specification like NTSC or the direct speaker-driving signal of analog audio. Physical characteristics of the electrical or optical equipment includes the types and numbers of wires required, voltages, frequencies, optical intensity, and the physical design of the connectors. Any data link layer details define how application data is encapsulated. Application layer details define the actual audio or video format being transmitted, often incorporating a codecs not specific to the interface, such as PCM, MPEG-2, or the DTS Coherent Acoustics codec. In some cases, the application layer is left open; for example, HDMI contains an Ethernet channel for general data transmission.

USB-C 24-pin USB connector system

USB-C is a 24-pin USB connector system with a rotationally symmetrical connector.

References

  1. Engst, Adam; Pogue, David (1999-11-23). Crossing Platforms – A Macintosh/Windows Phrasebook: A Dictionary for Strangers in a Strange Land. O'Reilly Media. ISBN   978-1-4919-1679-7 . Retrieved 2021-02-16.
  2. 1 2 "VGA Cables - A Complete Buyers' Guide | RS Components". uk.rs-online.com. Retrieved 2020-08-16. The terminology here is sometimes used rather interchangeably when it comes to labelling various types of VGA cable and can be a little vague. However, the basic or standard VGA connector type will usually be referred to as some variant of the following: DE-15, HD15, VGA plug, SVGA plug, D-Sub 15 or D-Subminiature, or the more generic RGB connector.
  3. Shah, Agam (2012-07-31). "VGA ports bowing out of home computers, lingering in the workplace". Computerworld. Retrieved 2020-08-16.
  4. Cables2Go catalog (PDF).
  5. VESA DDC/CI Standard Version 1.1. 2004. p. 31. DDC/CI supports hot plugging, provided the display can detect a disconnection of the video cable
  6. 1 2 "Video Subsystem (Type 1)". IBM Personal System/2 Hardware Interface Technical Reference (PDF) (First ed.). IBM. May 1988. Archived from the original (PDF) on 2018-05-14. Retrieved 2021-02-16.
  7. VESA Enhanced Display Data Channel Standard Version 1.1. Video Electronics Standards Association. 2004-03-24. p. 18.
  8. "IBM PS/55 モデル5550-S/T/V 各種ピン割り当て". Diary on wind. 2015-12-28. Retrieved 2019-05-26.
  9. "Re: 8514A emulator". fj.sys.ibmpc. 1993-01-27. Retrieved 2019-05-27.
  10. "The Nexus: Projects - VGA to SCART Converter". Nexusuk.org. 2013-06-26. Retrieved 2013-10-21.
  11. "VGA to TV converter page". Epanorama.net. Retrieved 2013-10-21.