GB1244949A - Character generator - Google Patents

Abstract

1,244,949. Cathode ray tube displays. STROMBERG DATAGRAPHIX Inc. 7 April, 1970 [29 April, 1969], No. 16323/70. Heading H4T. A C.R.T. character display system in which the beam moves successively in a number of straight-line segments derives the three control signals (X, Y and intensity) from a set of three output lines, one set being provided for each character, the lines being selectively threaded through magnetic cores which are energized in turn to generate the segmental signals. As shown the set of three lines 13 corresponding to the required character are selected at 22, and cores 11 through which the lines may be threaded (in either sense) are energized in turn by a series of blocking oscillators in pulse generator 13. The induced signals (positive, negative or zero) control at 27 or 28 the supply of positive or negative current to capacitor 16 or 17, and thus each core when energized controls the X and Y deflection corresponding to one of the segmental elements of a character. The third wire controls, according as it is threaded or not, the blanking or unblanking of the beam. Two types of display are described, one in which line segments are drawn by a moving spot, and the other where the beam is blanked during movement and then brightened to give a dot display, the differences in the apparatus lying mainly in the intensity control circuit 39. The basic repertory of segmental movements is horizontal, vertical and diagonal, corresponding to X only, Y only and X plus Y incremental signals, but additional flexibility is provided by a proportioning circuit 41 which for selected characters controls the addition to or subtraction from the standard valve capacitances 16 or 17, thus altering the direction of the diagonal segments. In the case of " drawn-line " segments signals indicating this proportioning pass to intensity circuit 39 (as do also signals representing the X and Y movements) to allow compensation of beam intensity for linear trace speed. In a modification the X and Y trace speeds may be signalled independently as 0, Π1 or Π2 units by the use of five lines 13 instead of the two lines shown, the signals on the five lines passing to a decoder controlling the charging circuits. Eighteen cores 11 are described as adequate for character tracing; since many characters require substantially less time may be saved by the use of an additional " stop " wire threaded through the core following that of the last segment. The circuits 14 may be so designed that instead of requiring an input pulse from 13 for each increment of charge to be supplied to their capacitors, the charging is initiated by a first pulse and terminated by a second, thus permitting a more even trace speed. Circuitry for the various units is illustrated and described.