GB1343298A - Crt display systems - Google Patents

Abstract

1343298 Cathode-ray tube displays MULLARD Ltd 30 July 1971 36054/71 Heading H4T In a cathode-ray tube (CRT) display system for Alpha-Numeric characters produced in dot matrix form by selective bright-up of the tube beam as it is scanned on a conventional television line raster, each row of character elements (dots) being repeated once in the next successive line scan to increase the height of the characters, the shape of such characters is improved by increasing the lengths of selected ones of the character elements to produce a "rounded-off" effect. Fig. 2 shows the characters "A" and "B" composed of elements (each of two matrix units in length) each of which is repeated once in the next successive scan and Fig. 3 shows the manner in which the "rounding-off" is produced by increasing the lengths of certain ones of the elements such elements being determined in accordance with specified conditions dependent on the presence or absence of elements in adjacent positions in the same row and in the preceding and succeeding rows and in corresponding positions in the latter two rows. These conditions are sensed by a "cursor" unit CU, Fig. 4, which comprises nine bi-stable devices A to I cascade connected in sets I, H, G; F, E, D; and C, B, A, the first set being fed with character data in serial form from a parallel to serial converter PSC supplied from a "readonly" memory ROM and the other two sets with the same data after delay of one character row in a shift register SR1, supplying set D, E, F and after a further one character row delay in shift register SR2 supplying set A, B, C. Thus, considering the condition "1" or "0" bistable E ("1" indicating that a character element is to be produced and "0" that a character element is not to be produced) as relating to a character element position just prior to it being reached by the scanning beam, such as position P1 (Figs. 3 and 3a), the conditions of the other eight bi-stables indicate whether character elements have or have not already been produced (bi-stables A to D) and whether or not character elements are to be produced (bi-stables F to I). Following the consideration set out above bi-stable conditions E, G, H, D and E, A, B, D indicate that the character element considered is to be lengthened to the left hand side and bi-stable conditions E, I, H, F, and E, C,F, B, that the character element is to be lengthened to the right hand side and to effect this the outputs of the bi-stables concerned with left hand side lengthening are utilized to provide a beam bright-up signal ("write early") which precedes the normal element producing (writing) signal and the outputs of the bi-stables concerned with right hand side lengthening are utilized to provide a beam bright-up signal ("write late") which follows the normal writing signal.