High resolution graphics card (6)

This sixth article in the series deals with the colour extension, which is basically a large amount of extra RAM (Random Access Memory) for the main (monochrome) card One extension is sufficient for up to sixteen colours on two or four screen pages. HIGH-RESOLUTION COLOUR GRAPHICS CARD 6 The colour extension card contains three identical sections, each com- prising a 64 Kbyte memory bank; a shift register; RMW circuitry; and colour decoding logic for memory write operations. In theory, any number of extensions could be added to the main card, but in most practical cases one will suffice to provide up to sixteen colours. Adding an intensity bit In the very first part of this series, published in the September 1985 issue of Elektor Electronics, block schematic diagrams of the monochrome and full colour systems were presented in Figures la and lb respectively. For reasons of clarity, Fig. lb then showed an 8-colour RGB configuration with three memory planes. However, with a completed...