Patent US 3,988,728

A graphic display device of the type which receives instructions from an external computer and, by successively scanning the rasters of a display matrix, displays patterns such as alphanumeric characters, symbols, etc. upon a cathode ray tube. The graphic display device has a pattern generator which stores patterns in raster form and generates signals for forming such patterns upon receipt of a pattern address signal designating the particular pattern to be formed, and a repeating raster designation signal designating the particular raster of stored pattern information to be accessed for each scan of the display matrix. Pursuant to the invention, the graphic display device comprises pattern shifting means for shifting, on demand and in an amount selected by the external computer, the display of a pattern in a direction transverse to the direction of raster scanning. The pattern shifting means comprises means for modifying the raster designation signal applied to the pattern generator to thereby relocate the individual rasters of the stored pattern within the display matrix being scanned. Pattern shifts thus may be effected without requiring the pattern generator to store additional pattern formation data.