Color index conversion system in graphic display device

Abstract

A color graphic display device for converting color index data read out from a plurality of frame memories to color information on a screen so as to perform graphic display has a first register for holding a group number determined in accordance with a combination of areas between copy source and destination memories of the plurality of frame memories for an interarea copy, and a ROM table for storing conversion color index data at a plurality of addresses of the group number and for receiving as address data linked data of an output from the first register and the color index data from the plurality of frame memories. The group number is set in the first register and the corresponding color index data is read out from the frame memories, thereby obtaining updated or converted color index data from the ROM table. The color graphic display device also has a second register for holding write enable/disable data for specifying the write enable/disable mode of the plurality of frame memories. The write enable/disable data is set in the second register so as to specify the copy destination frame memories, and the specific bits of the converted color index data are thereby selectively written only in the copy destination frame memories.