VGA connector

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VGA connector (DE-15/HD-15)


A female DE-15 plug on a laptop

Type Analogue computer video connector
Production history
Designer IBM based on D-subminiature
Designed 1987
Produced 1987 to present
Superseded by DVI (1999)
Specifications
Video signal RGB video signal plus option H and V sync
Data signal I²C data channel for DDC information
Pins 15
Connector DE-15
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 N/C Not connected
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 SENSE +5 V DC from gfx adapter
Pin 10 GND Ground (VSync, DDC)
Pin 11 N/C Monitor ID
Pin 12 SDA I²C data
Pin 13 HSync Horizontal sync
Pin 14 VSync Vertical sync
Pin 15 SCL I²C clock
The image and table details the newer 15-pin VESA DDC2 connector. Note that the pin numbering in the diagram is a female connector at the graphics adapter. This is also the wire numbering that will be seen from the wire and solder side of the male connector. The pin numbering on the male connector, usually the cable end, is the mirror image.

A VGA connector as it is commonly known (other names include RGB connector, D-sub 15, mini sub D15 and mini D15) is a three-row 15 pin DE-15. There are four versions: original and DDC2 pinouts, the far older and less flexible DE-9 connector, and a Mini-VGA used for laptops.

The common 15-pin VGA connector found on most video cards, computer monitors, high definition televisions which support VGA connections, and other devices, is almost universally called "HD-15". HD stands for "high-density", which distinguishes it from connectors having the same form factor but only 2 rows of pins. However, this connector is often incorrectly referred to as a DB-15 or HDB-15.[citation needed]

"VGA connectors" and their associated cabling are always used solely to carry analog component RGBHV (red - green - blue - horizontal sync - vertical sync) video signals along with DDC2 digital clock and data.

Where size is a constraint (such as laptops) a mini-VGA port can sometimes be found in place of the full-sized VGA connector

Contents

[edit] Disabling DDC

On Microsoft Windows (windows XP and above), there is no software provided option to disable plug and play monitor detection.[citation needed] This causes problems with computer/monitor switching applications and causes computer games to select display resolutions higher than the monitor is physically capable of displaying resulting in a garbled display.

In these circumstances, it may be necessary to remove pin 12 from the monitor VGA cable, to disable plug and play monitor detection. This allows display resolution to be selected manually and not overridden when the display adapter is removed and reinserted or the KVM switch is operated.

The automatic plug-and-play monitor detection under Windows operating systems can be overridden in the video card's control panel when the appropriate third-party driver is installed.

[edit] KVM switch problems

There are two problems with VGA and KVM switches: the pin-12 problem and the pin-9 problem.

[edit] The pin 12 problem

As mentioned under 'Disabling DDC', a machine connected to a KVM switch, but during startup not connected throughout the KVM switch to the console, will fall back to the default (lower) resolution. The solution is to remove the pin from one end of the VGA cable and to disable any plug and play for the monitor. Under linux you will need to edit /etc/X11/xorg.conf:

   Option "metamodes" "nvidia-auto-select +0+0"

becomes

   Option "metamodes" "1280x1024_60 +0+0; nvidia-auto-select +0+0"

But you can startup with a normal (full featured) VGA cable directly connecting your machine to the montior, letting it do 'plug and play'. Once it is up and running, do have a look into /etc/X11/xorg.conf and keep a copy of that file. Then do your static configuration based on the things you found in /etc/X11/xorg.conf.

[edit] The pin 9 problem

There exists another KVM problem: the pin 9 problem. Some monitors wait for a valid +5V level (TTL) on pin 9, using this signal to detect the computer. If the KVM switch doesn't provide +5V (pin 9 is floating) or pin 9 is missing on the connector of the cable, the monitor will not startup properly (sometimes the I/O light will flash slowly). The solution is to hardwire the console-side pin 9 of the KVM switch to +5V and ensure that the cable between the KVM switch and console has a wired pin 9.

[edit] See also

[edit] External links

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