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Storing and Selecting Color Information for Character and Background Display

IP.com Disclosure Number: IPCOM000047980D
Original Publication Date: 1983-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Kurtz, RC: AUTHOR

Abstract

In designing a color monitor adapter, it was desired to maintain maximum compatibility with the software used to control the existing 25-line monochrome monitor. Because of this need, it was not possible to use attribute bits already defined in the 25-line display to code the color information and keep the flexibility to make any single character any of the seven available colors. Moreover, maximum flexibility in a color display monitor would not only permit any character box to display a character in any of the seven available colors but, in addition, would permit the display of the background filed in the "inverse" of the character or in any of the other remaining colors. As shown in the figure, the problem of insufficient attribute space is solved by adding a 2Kx4-bit section of color memory to store color information.

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Storing and Selecting Color Information for Character and Background Display

In designing a color monitor adapter, it was desired to maintain maximum compatibility with the software used to control the existing 25-line monochrome monitor. Because of this need, it was not possible to use attribute bits already defined in the 25-line display to code the color information and keep the flexibility to make any single character any of the seven available colors. Moreover, maximum flexibility in a color display monitor would not only permit any character box to display a character in any of the seven available colors but, in addition, would permit the display of the background filed in the "inverse" of the character or in any of the other remaining colors. As shown in the figure, the problem of insufficient attribute space is solved by adding a 2Kx4-bit section of color memory to store color information. Each color memory location is given an address 10000 (hexadecimal value) above the corresponding character memory location by the color memory decode logic. With this method, the system control does not need more data lines to store the color information. Instead, the controller must do two writes (character and color) to store a character in the adapter. The color storage consists of assigning each bit a color. The state of the bit determines whether or not a particular color gun in the monitor is turned on. To provide the complementary colors, the appropriate bits are set or cleared, turning on or off each of the color guns. For example, yellow is obtained by storing bits which turn on the green and red color guns and turn off the blue color gun. In order to display the character on a background field of its "inverse" color, the character color outputs are complimented. The bit required to select this function is present with no further design change. This is because the four-bit memory is...