GB1078545A - Character display apparatus - Google Patents

Abstract

1,078,545. Cathode - ray tube displays. INTERNATIONAL BUSINESS MACHINES CORPORATION. Feb. 14, 1966 [March 1, 1965], No. 6354/66. Heading H4T. In a character display apparatus in which Alpha-Numeric characters are produced on a cathode-ray tube by appropriate deflections of the beam data indicative of each character derived from a register store are utilized to control a group of logic elements associated with such character, the elements of each group controlling in sequence appropriate combinations of beam deflection generators. The data, which may be derived from a computer or a keyboard operated device, are set up in coded digital forms in a register (12, Fig. 1) and fed to a decoder (14) which supplies a predetermined voltage level on a different line for each coded input to an End Point Generator (16). This supplies signals in digital form indicative of the successive X, Y co-ordinates of the end point of each stroke required to trace the character (starting from a fixed origin X=0, Y=0) together with signals indicative of the strokes which must be blanked, to preserve uniformity of trace brightness, and a further signal indicative of the last stroke of the character (end-bit). Thus, generator (16) comprises a group of logic elements for each character, specifically AND gates (30-1 . . . 30-4, Fig. 3) appertaining to the character A which requires four strokes (Fig. 2b) and e.g. gates (30-1 . . . 30-0) appertaining to the character G which requires nine strokes (Fig. 2a)-the maximum number provided-including the stroke from the origin "0" to the commencement of the character end-point (EP) X=3, Y=3, with similar appropriate groupings of AND gates for each of the remaining characters (Fig. 4). In operation, a predetermined voltage level on the appropriate character output line of decoder (14) forms one input of all of the appertaining AND gates which are then sequentially conditioned to produce output signals by the successive outputs from a counter (18)-producing a maximum count of nine-such output signals controlling OR gates producing digital signals appropriate to the amount of X and Y deflection which each stroke requires together with signals controlling the stroke blanking and signals indicative of the end of the character. The latter signals (END BIT) are fed via a gate (22) and register (24) to re-set the counter (18)-i.e. to improve the time efficiency of operation when the character requires less than nine strokes-and the other signals are supplied via digital to analogue converters to produce the required blanking and beam deflection signals. The latter are fed to one deflection circuit whilst an auxiliary deflection circuit is employed for positioning the beam initially at the origin, X=0, Y=0.