VGA connector

Not to be confused with Video Graphics Array.
VGA connector (DE-15/HD-15)

A female DE-15 output in a laptop computer.
Type Computer analog video connector
Production history
Designer IBM based on D-subminiature
Designed 1987
Produced 1987 to present
Superseded by DVI (1999)
General specifications
Hot pluggable Depends
Video signal RGB video signal plus option H and V sync
Pins 15
Connector DE-15
Data
Data signal I²C data channel for DDC information
Pin out
A female DE15 socket (videocard side).
Pin 1 RED Red video
Pin 2 GREEN Green video
Pin 3 BLUE Blue video
Pin 4 ID2/RES formerly Monitor ID bit 2, reserved since E-DDC
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 formerly key, now +5V DC
Pin 10 GND Ground (VSync, DDC)
Pin 11 ID0/RES formerly Monitor ID bit 0, reserved since E-DDC
Pin 12 ID1/SDA formerly Monitor ID bit 1, I²C data since DDC2
Pin 13 HSync Horizontal sync
Pin 14 VSync Vertical sync
Pin 15 ID3/SCL formerly Monitor ID bit 3, I²C clock since DDC2
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 mirror image of the cable’s wire-and-solder side.

A Video Graphics Array (VGA) connector is a three-row 15-pin DE-15 connector. The 15-pin VGA connector is found on many video cards, computer monitors, and high definition television sets. On laptop computers or other small devices, a mini-VGA port is sometimes used in place of the full-sized VGA connector.

DE-15 has been conventionally referred to ambiguously as D-sub 15, incorrectly as DB-15 and often as HD-15 (High Density, to distinguish it from the older and less flexible DE-9 connector used on old VGA cards, which has the same E shell size but only two rows of pins).

VGA connectors and cables carry analog component RGBHV (red, green, blue, horizontal sync, vertical sync) video signals, and VESA Display Data Channel (VESA DDC) data. In the original version of DE-15 pinout, one pin was keyed by plugging the female connector hole; this prevented non-VGA 15 pin cables from being plugged into a VGA socket. Four pins carried Monitor ID bits which were rarely used; VESA DDC redefined some of these pins and replaced the key pin with +5 V DC power supply.

The VGA interface is not engineered to be hotpluggable (so that the user can connect or disconnect the output device while the host is running), although in practice this can be done and usually does not cause damage to the hardware or other problems. However, nothing in the design ensures that the ground pins make a connection first and break last, so hotplugging may introduce surges in signal lines which may or may not be adequately protected against. Also, depending on the hardware and software, detecting a monitor being connected might not work properly in all cases.

Cable quality

A VGA cable with DE-15 male connector

The same VGA cable can be used with a variety of supported VGA resolutions, ranging from 640×350px @70 Hz (24 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 which make them thicker. A quality cable should not suffer from signal crosstalk which occurs when the signals in one wire induce unwanted currents in adjacent wires, ghosting which occurs when impedance mismatches cause signals to be reflected (note that ghosting with long cables may not be the fault of the cable but may instead be caused by equipment with incorrect termination or by use of passive splitters), and other signal degradation effects; shorter VGA cables are less likely to introduce significant degradation.

VGA BNC connectors

Some high-end monitors and video cards featured 5 separate BNC connectors for RGBHV signal, allowing highest quality connection using five 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.

Adapters

There are DVI to VGA adapters and cables. They do not carry audio channels, thus separate path for audio should be used, if needed.

To connect VGA to interfaces with different signaling and vice versa converters may be used. Most of them need an external power source to operate and are inherently lossy.

VGA to SCART converter that passes through color information is possible, because VGA — SCART RGB signals are electrically compatible, except for synchronization. Modern graphics adapters are able to widely modify their signal in software, including refresh rate, sync length, polarity and number of blank lines. Particular issues include whether or not interlacing is supported as well as if the resolution can be set to 720×576 in PAL countries. Under these strict conditions, a simple circuit to combine the VGA separate synchronization signals into SCART composite sync may suffice.[1][2]

See also

References

  1. ↑ "The Nexus: Projects - VGA to SCART Converter". Nexusuk.org. 2013-06-26. Retrieved 2013-10-21.
  2. ↑ "VGA to TV converter page". Epanorama.net. Retrieved 2013-10-21.

External links

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