Date of this Version
United States Patent Low et al. 3,648,250
A digital video display system (DWDS) is disclosed for display of image, alphanumeric and other data on a cathode-ray tube (CRT) with sequential raster scan and two, four or eight gray shades. The DVDS includes a central processing unit for ac tivating the system, selecting the X (horizontal axis) and Z (in tensity modulation) modes, and designating the starting loca tion of two successive rasters of data from a memory accessed by a data multiplexer subsystem (DMS). At the end of each raster, the DMS interrupts the computer for a new starting lo cation of a raster of data to follow the next while a DVDS con trol subsystem is prepared for the next raster. The first word of raster data designates the Y-axis value to be transmitted to the CRT vertical deflection system through a static digital-to analog converter. Each word thereafter contains a predeter mined number n of bits for n/3, n/2 or nil display elements (DE) in the respective eight, four and two gray shade modes. DE groups are transmitted to the CRT intensity control through a static digital level select network. As each DE group is read, an X-axis integrator is incremented by one, two or four units depending upon the X-axis mode selected. A counter determines when all DE groups of a word have been displayed in each of the gray shade modes, and resets all of the DVDS, thereby shutting off display after one, two or three DMS memory cycles in the eight, four and two gray shade modes, respectively, until the next word is automatically read out of memory as a separate counter in the DVDS keeps track of the DMS-memory cycles for the different gray shade modes.