CRT Controller with Increased Addressing Capability
Original Publication Date: 1982-Sep-01
Included in the Prior Art Database: 2005-Feb-10
The scan line addresses provided by a conventional cathode ray tube (CRT) controller are normally used to select the scans of a character from a character generator. For instance, in the 6845 chip manufactured and sold by Motorola, the RA0 through RA4 scan address lines scan the character generator contained in a conventional read only memory. Normally the addresses are incremented from 0 to the program number of scans per character. By using the RA0 through RA4 lines as direct memory addresses to a character buffer or graphics buffer, one can expand the addressing capability of the CRT controller to up to 512 kilobytes. This capability gives the CRT controller a wide range of uses, such as using the scan address lines to implement a 640 X 200 pixel (picture element) graphics display using a 16K-byte graphics buffer.