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Monochrome Display Driven by Color System

IP.com Disclosure Number: IPCOM000062298D
Original Publication Date: 1986-Nov-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 2 page(s) / 48K

Publishing Venue

IBM

Related People

Anwyl, ED: AUTHOR [+2]

Abstract

A color display system generates a differential 8-level output from a digital-to-analog converter (DAC) for each of three colors. When using these three color outputs to drive a monochrome display, the outputs of two DACs are wired together to provide a differential 16-level monochrome grey scale drive signal. Alternatively, the outputs of three DACs are mixed by a matching impedance network to provide a 24-level monochrome drive signal. Fig. 1 shows a portion of a typical all-points-addressable (APA) display system. Eight bit planes are shown, each plane typically carrying one storage cell position for each picture element (pel) on the CRT screen. By the use of multiple bit planes, each pel can have a variable color assigned to it.

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Monochrome Display Driven by Color System

A color display system generates a differential 8-level output from a digital-to- analog converter (DAC) for each of three colors. When using these three color outputs to drive a monochrome display, the outputs of two DACs are wired together to provide a differential 16-level monochrome grey scale drive signal. Alternatively, the outputs of three DACs are mixed by a matching impedance network to provide a 24-level monochrome drive signal. Fig. 1 shows a portion of a typical all-points-addressable (APA) display system. Eight bit planes are shown, each plane typically carrying one storage cell position for each picture element (pel) on the CRT screen. By the use of multiple bit planes, each pel can have a variable color assigned to it. The bit planes are read out to a palette storage array of which a typical size is shown in Fig. 1. An array of this size allows 3 bits of output to define 8 intensity levels for each of red, green and blue signals sent to the appropriate guns in a CRT. The example shown allows for the use of 256 concurrent colors from a total menu of 512. The control program of the terminal is to be able to read and write the palette storage array, and thus has control of logical-to-physical color conversion. Although monochrome monitors only require the single channel, they typically require more levels for use as grey scale than does a single channel on a 3-channel color system. In the example shown in Fig. 1, for instance, a monochrome monitor could be plugged into either the red, green or blue channel, but would be thus limited to 8 levels of grey scale, compared with 512 hues in the color version. In a typical color system, a multi-pin plug will attach to the 6 signal points shown in addition to connectors for sync and ground. Fig. 2 shows how the plugging for monochrome combines the output for 2 DACs to give additional vo...