Patent GB-1280971-A (GB)
Title: Visual display system for storage device
IPC: G09G5/32
Filed: 1970-01-01
Abstract: 1280971 Cathode-ray tube displays INTERNATIONAL BUSINESS MACHINES CORP 1 Jan 1970 [10 Jan 1969] 127/70 Heading H4T [Also in Division G4] A visual display system scans a beam of radiation over a display surface in accordance with a primary raster so that the beam passes sequentially through all the display positions on the surface each corresponding to a respective storage position of a data store, the beam being additionally scanned at each display position in accordance with a secondary raster, the intensity of the visible spot produced by the beam being controlled to a predetermined value during the whole of each secondary raster in accordance with the contents of the corresponding storage position. In a character recognition system, the store is a shift register composed of a 10 column, 14 row array of bit cells fed from a character scanner to form an electric digitized representation of the character from which the character is recognized by recognition logic (no details given). The register is shifted out from the bottom of the last column to a CRT display where each 1 bit brightens a corresponding secondary raster (6 short horizontal lines), the 14 x 10 secondary rasters being disposed in matrix array on the primary raster (10 vertical lines). Each vertical line of the primary raster is started at a seek position at the bottom of the line. Horizontal and vertical integrating amplifiers drive the CRT deflection drivers and their outputs are compared with reference voltages in first and second discriminators to indicate passing of the horizontal position of the first seek point and the common vertical position of all the seek points. The horizontal output is also fed to a track hold amplifier and a differential amplifier, the latter receiving the output of the track hold amplifier. The output of the differential amplifier, after voltage adjustment using resistors, is compared with a reference in a third discriminator to indicate passing of the horizontal position of seek points after the first. The track hold amplifier follows the horizontal deflection voltage during (the secondary rasters on) each vertical line of the primary raster to derive the next seek point horizontal position. A 14 position (i.e. count) binary counter counts the secondary rasters in each primary raster line, a 6 position binary counter counts the horizontal lines in each secondary raster, a 3 position ring counter counts to 2 during each of these horizontal lines and increments to 3 for the vertical line between successive horizontal lines. The bottom and one side of each secondary raster are also brightened under control of the second and third of these counters. A 10 position counter counts the lines of the primary raster. Error detection.-A switch is provided permitting the display to be controlled from the bottom of any of the columns of the shift register rather than just from the bottom of the last column. If a register failure has occurred and the register appears (from the display) to contain all black bits, successive positions of the switch are tried until the register appears to contain all white bits to indicate the faulty column. Similarly, if the register appears all white, black bits are inserted at the top of the first column and successive positions tried until the register appears to contain all black bits.