Enhanced Graphics Adapter

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Color palette

EGA Color Table

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 standard built on this by allowing each of the 64 colors to be further customized. dell optiplex gx260

The full 64-color EGA palette compaq presario 5000

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. dell optiplex gx240

Default EGA 16-color palette

(set up to match the standard CGA 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.

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

Resolution H x V

640 x 350 other modes available

H-freq

15.7 or 21.8 kHz

V-freq

60 Hz

Colors

6-bit (64)

See also

Graphics card

Graphics processing unit

List of display interfaces

List of monochrome and RGB palettes 6-bit RGB section

List of 16-bit computer hardware palettes EGA section

Professional Graphics Controller

References

Mueller, Scott (1992) Upgrading and Repairing PCs, Second Edition, Que Books, ISBN 0-88022-856-3

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