Enhanced Graphics Adapter - AbsoluteAstronomy.com

The Enhanced Graphics Adapter (EGA) is the IBM PC

IBM PC

The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981...

computer display standard

Computer display standard

Computer display standards are often a combination of aspect ratio, display resolution, color depth, and refresh rate.This article describes the different display standards for computer displays.-History:...

specification which is between CGA

Color Graphics Adapter

The Color Graphics Adapter , originally also called the Color/Graphics Adapter or IBM Color/Graphics Monitor Adapter, introduced in 1981, was IBM's first color graphics card, and the first color computer display standard for the IBM PC....

and VGA

Video Graphics Array

Video Graphics Array refers specifically to the display hardware first introduced with the IBM PS/2 line of computers in 1987, but through its widespread adoption has also come to mean either an analog computer display standard, the 15-pin D-subminiature VGA connector or the 640×480 resolution...

in terms of color and space resolution. Introduced in October 1984 by IBM shortly after (but not exclusively for) its new PC/AT

IBM Personal Computer/AT

The IBM Personal Computer AT, more commonly known as the IBM AT and also sometimes called the PC AT or PC/AT, was IBM's second-generation PC, designed around the 6 MHz Intel 80286 microprocessor and released in 1984 as machine type 5170...

, EGA produces a display of 16 simultaneous colors from a palette of 64 at a resolution of up to 640×350 pixels. The EGA card includes a 16 KB

Kibibyte

The kibibyte is a multiple of the unit byte for quantities of digital information. The binary prefix kibi means 1024; therefore, 1 kibibyte is . The unit symbol for the kibibyte is KiB. The unit was established by the International Electrotechnical Commission in 1999 and has been accepted for use...

ROM

Read-only memory

Read-only memory is a class of storage medium used in computers and other electronic devices. Data stored in ROM cannot be modified, or can be modified only slowly or with difficulty, so it is mainly used to distribute firmware .In its strictest sense, ROM refers only...

to extend the system BIOS

BIOS

In IBM PC compatible computers, the basic input/output system , also known as the System BIOS or ROM BIOS , is a de facto standard defining a firmware interface....

for additional graphics functions, and includes the Motorola

Motorola

Motorola, Inc. was an American multinational telecommunications company based in Schaumburg, Illinois, which was eventually divided into two independent public companies, Motorola Mobility and Motorola Solutions on January 4, 2011, after losing $4.3 billion from 2007 to 2009...

MC6845 video address generator

Video Display Controller

A Video Display Controller or VDC is an integrated circuit which is the main component in a video signal generator, a device responsible for the production of a TV video signal in a computing or game system...

as used in the CGA.

Each of the 16 colors can be assigned a unique RGB color code via a palette

Palette (computing)

In computer graphics, a palette is either a given, finite set of colors for the management of digital images , or a small on-screen graphical element for choosing from a limited set of choices, not necessarily colors .Depending on the context In computer graphics, a palette is either a given,...

mechanism in the 640×350 high-resolution mode; the 64 palette colors are a balanced RGB color set comprising all possible combinations of two bits per pixel for red, green and blue. EGA also includes full 16-color versions of the CGA 640×200 and 320×200 graphics modes; only the 16 CGA/RGBI colors are available in these modes. EGA 4-bit (16 colors) graphic modes

All Points Addressable

All Points Addressable , in the context of a video monitor, dot matrix or any display device consisting of a pixel array, refers to an arrangement bits or cells which can be individually manipulated, as opposed to rewriting the whole array every time a pixel changes.Generally, text modes are not...

are also notable for a sophisticated use of bit plane

BIT plane

This article is about Natalie Jeremijenko and the Bureau of Inverse Technology's project. For the company, see Bitplane. For the digital information term, see bit plane....

s and mask registers

Hardware register

In digital electronics, especially computing, a hardware register stores bits of information, in a way that all the bits can be written to or read out simultaneously.The hardware registers inside a central processing unit are called processor registers....

together with CPU bitwise operation

Bitwise operation

A bitwise operation operates on one or more bit patterns or binary numerals at the level of their individual bits. This is used directly at the digital hardware level as well as in microcode, machine code and certain kinds of high level languages...

s, which constitutes an early graphics accelerator inherited by VGA

Video Graphics Array

and numerous compatible hardware.

The original CGA modes are also present, though EGA is not 100% hardware compatible with CGA. EGA can drive an MDA

Monochrome Display Adapter

The Monochrome Display Adapter introduced in 1981 was IBM's standard video display card and computer display standard for the PC. The MDA did not have any pixel-addressable graphics modes...

monitor by a special setting of switches on the board; only 640×350 high-resolution monochrome graphics and the standard MDA text mode are available in this mode.

EGA cards use the PC ISA

Industry Standard Architecture

Industry Standard Architecture is a computer bus standard for IBM PC compatible computers introduced with the IBM Personal Computer to support its Intel 8088 microprocessor's 8-bit external data bus and extended to 16 bits for the IBM Personal Computer/AT's Intel 80286 processor...

bus and were available starting in 8-bit versions. The base IBM EGA card came with 64 KB of video memory

Video memory

Video memory is a term generally used in computers to describe some form of writable memory, usually RAM, dedicated to the purpose of holding the information necessary for a graphics card to drive a display device...

installed, only enough for 4 colors in high-resolution graphics. Expansion to 256 KB required a daughterboard

Daughterboard

A daughterboard, daughtercard or piggyback board is a circuit board meant to be an extension or "daughter" of a motherboard , or occasionally of another card...

. Eventually, most EGA cards and clones would come with 256 KB of memory. A few third-party EGA clones (notably the ATI Technologies

ATI Technologies

ATI Technologies Inc. was a semiconductor technology corporation based in Markham, Ontario, Canada, that specialized in the development of graphics processing units and chipsets. Founded in 1985 as Array Technologies Inc., the company was listed publicly in 1993 and was acquired by Advanced Micro...

and Paradise

Western Digital

Western Digital Corporation is one of the largest computer hard disk drive manufacturers in the world. It has a long history in the electronics industry as an integrated circuit maker and a storage products company. Western Digital was founded on April 23, 1970 by Alvin B...

boards) feature a range of extended graphics modes (e.g., 640×400, 640×480 and 720×540), as well as automatic monitor type detection, and sometimes also a special 400-line interlace mode for use on CGA monitors.

The EGA standard was made obsolete by the introduction of VGA by IBM in April 1987 with the PS/2

IBM Personal System/2

The Personal System/2 or PS/2 was IBM's third generation of personal computers. The PS/2 line, released to the public in 1987, was created by IBM in an attempt to recapture control of the PC market by introducing an advanced proprietary architecture...

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|Sample of text mode

Text mode

Text mode is a kind of computer display mode in which the content of the screen is internally represented in terms of characters rather than individual pixels. Typically, the screen consists of a uniform rectangular grid of character cells, each of which contains one of the characters of a...

characters
with cursor.
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Color palette

The EGA palette allows all 16 CGA colors to be used simultaneously, and it allows substitution of each of these colors with any one from a total of 64 colors (two bits each for red, green and blue). This also allows the CGA's alternate brown color to be used without any additional display hardware. The later VGA

Video Graphics Array

standard built on this by allowing each of the 64 colors to be further customized.

When selecting a color from the EGA palette, two bits are used for the red, green and blue channels. This allows each channel a value of 0, 1, 2 or 3. To select the color magenta, the red and blue values would be medium intensity (2, or 10 in binary) and the green value would be off (0). When calculating the intended value in the 64-color EGA palette, the binary number of the intended entry is of the form "rgbRGB" where a lowercase letter is the least significant bit of the channel intensity and an uppercase letter is the most significant bit. For magenta, the most significant bit in the red and blue values is a 1, so the uppercase R and B placeholders would become 1. All other digits are zeros, giving the binary number 000101 for the color magenta. This is 5 in decimal, so setting a palette entry to 5 would result in it being set to magenta. All the color values for the default colors are listed in the table on the right.

Default EGA 16-color palette (set up to match the standard CGA Color Graphics Adapter The Color Graphics Adapter , originally also called the Color/Graphics Adapter or IBM Color/Graphics Monitor Adapter, introduced in 1981, was IBM's first color graphics card, and the first color computer display standard for the IBM PC.... colors)
Color	rgbRGB	Decimal
0 – black (#000000)	000000	0
1 – blue (#0000AA)	000001	1
2 – green (#00AA00)	000010	2
3 – cyan (#00AAAA)	000011	3
4 – red (#AA0000)	000100	4
5 – magenta (#AA00AA)	000101	5
6 – brown (#AA5500)	010100	20
7 – white / light gray (#AAAAAA)	000111	7
8 – dark gray / bright black (#555555)	111000	56
9 – bright blue (#5555FF)	111001	57
10 – bright green (#55FF55)	111010	58
11 – bright cyan (#55FFFF)	111011	59
12 – bright red (#FF5555)	111100	60
13 – bright magenta (#FF55FF)	111101	61
14 – bright yellow (#FFFF55)	111110	62
15 – bright white (#FFFFFF)	111111	63

Specifications

The EGA uses a female 9-pin D-subminiature (DE-9) connector which looks identical to the CGA connector. The hardware signal interface, including the pin configuration, is largely compatible with CGA. The differences are in the repurposing of three pins for the EGA's secondary RGB signals: the CGA Intensity pin (pin 6) has been changed to Secondary Green (Intensity); the second ground of CGA (pin 2) has been changed to Secondary Red (Intensity), and pin 7 (Reserved on the CGA) is used for Secondary Blue (Intensity). If the EGA is operated in the modes having the same scan rates as CGA, a connected CGA monitor should operate correctly, though if the monitor connects pin 2 to ground, the shorting of the EGA's Secondary Red (Intensity) output to ground could conceivably damage the EGA adapter. Similarly, if the CGA monitor is wired with pin 2 as its sole ground (which is poor design), it will not work with the EGA, though it will work with a CGA. Finally, because of the use of the CGA's Intensity pin as Secondary Green, on a CGA monitor connected to an EGA, all CGA colors will display correctly, but all other EGA colors will incorrectly display as the standard CGA color which has the same values for the g, R, G, and B bits (ignoring the r and b bits.) Conversely, an EGA monitor should work with a CGA adapter, but the Secondary Red signal will be grounded (always 0) and the Secondary Blue will be floating (unconnected), causing all high-intensity CGA colors except brown to display incorrectly and all colors to perhaps (but probably not) have a blue tint due to the indeterminate state of the unconnected Secondary Blue.

The IBM 5154 EGA monitor has a special IBM 5153 CGA compability mode when operating with CGA sync signals, and it will automaticly change to the CGA pinout to avoid all of the mentioned problems when operating in this mode.

Connector

Female DE-9, on EGA (computer).

Pin numbers (looking at socket): top row is pins 1-5, bottom row is pins 6 to 9, both numbered from right to left in this illustration.

**Pin assignments**
Pin	Name	Function
1	GND	Ground
2	SR	Secondary Red (Intensity)
3	PR	Primary Red
4	PG	Primary Green
5	PB	Primary Blue
6	SG	Secondary Green (Intensity)
7	SB	Secondary Blue (Intensity)
8	H	Horizontal Sync
9	V	Vertical Sync

Signal

Type	Digital, TTL
	640 × 350, other modes available
H-freq	15.7 or 21.8 kHz
V-freq	60 Hz
Colors	6-bit (64)

Color palette

Specifications

Connector

Signal

See also