Video Graphics Array
VGA is an acronym of Video Graphics Array i.e. prominent Video standard for PC screen display equipment. Technically, it is one of the categories of video adapter which circulatory manage the display screen. This outstanding graphic display system was developed by the IBM, generally provides 640 by 480 resolution with a refresh rate of 60 Hz and can display 16 colors simultaneously. But, this resolution is becoming too old-fashioned nowadays for the personal system thus, it is more suitable for mobile devices. VGA comprises of separate wires for transmitting signals of three color components and horizontal/vertical Synchronization and uses analog signals. Due to the analog signals, it is capable of low quality and resolutions display.
Present Status of VGA:
VGA standard is now replaced through SVGA, DVI, and HDMI cables and connector. However, this cable/connector is still applicable for some display devices and connections such as personal computers to a projector, television or a monitor.
VGA can carry only a video signal. Thus for another signal transmission along with the video signal, another cable is required.
Structure of a VGA connector:
The VGA connector is a 15-pin connector, containing 15 holes, each has its own size dimension and function. Role of the 15 pins of VGA connector is given below:
|Pins of VGA||Role|
|1st pin of VGA connector||For Red Video|
|2nd pin of VGA connector||For Green Video|
|3rd pin of VGA connector||For Blue Video|
|4th pin of VGA connector||For Monitor ID 2|
|5th pin of VGA connector||For TTL Ground|
|6th pin of VGA connector||Manage Red Analog Ground|
|7th pin of VGA connector||Manage Green Analog Ground|
|8th pin of VGA connector||Manage Blue Analog Ground|
|9th pin of VGA connector||Key|
|10th pin of VGA connector||Syn
|11th pin of VGA connector||Monitor
|12th pin of VGA connector||Monitor ID 1|
|13th pin of VGA connector||Horizontal Syn|
|14th pin of VGA connector||Vertical Syn|
|15th pin of VGA connector||Monitor ID 3|
The VGA supports Points Addressable graphics modes as well as the Alphanumeric text modes.
The most Standard graphics modes are given below:
a) 640 x 480 in 16 colors
b) 640 x 350 in 16 colors
c) 320 x 200 in 256 colors
d) 320 x 200 in 16 colors
The basic principle of VGA:
A colorful image is produced when the electron beam from a cathode ray tube strikes the fluorescent screen. For image generation,the electron beam scans the entire screen. The scanning mode can be categorized into the interlaced and progressive scan. During progressive scan, scanning starts from the top left corner of the screen and process point by point scans from left to right. After scanning one line, the electron beam further moves back to the left point of the next line and process continue. During this process, the cathode ray tube blanks electron beam. An image frame is then generated at that point.
There are four main constituents in VGA controller i.e. VGA interface signals, VGA interface definition, VGA timing control, VGA monitor and the VGA control signal.