Patent GB-1234580-A (GB)
IPC: G09G1/10
Filed: 1968-09-26
Abstract: 1,234,580. Cathode - ray tube displays. XEROX CORP. 26 Sept., 1968 [28 Sept., 1967], No. 45823/68. Heading H4T. In an arrangement for producing Alpha- Numeric characters &c. on the screen of a cathode-ray display tube by effecting appropriate deflections of the beam in a rectangular X, Y co-ordinate system, the deflecting waveforms are derived from the output of respective intergrators to the inputs of which selected ones of a plurality of trains of pulses, each train differing in frequency from the others, are selectively supplied in accordance with the character &c. to be displayed. Fig. 1, shows the general scheme in which a register 2, loaded, e.g. by a computer, supplies coded character designating signals to a decoder 4 the outputs of which energize the " set " wire in a character core matrix 6 corresponding to a selected character (see terminal 74, Fig. 3 and " set " wire(s) Ax, Ay, corresponding to the X and Y deflection requirements and beam blanking requirements for the character A). The matrix is " scanned " by sequential pulses from a clock controlled distributer 10 (which may comprise a ring counter) the outlets of which are connected to terminals 76 of the matrix, the scanning being effected from leftto-right. The output signals produced by the scanning comprise pulses on terminals 55 to 60 inclusive specifying X-deflection, pulses on terminals 61 to 63 inclusive, specifying Y- deflection, pulses on terminal 92 specifying beam blanking requirements, pulses on terminals 68 and 70 specifying, when present, negative values of the X and Y deflection quantities respectively and a pulse on terminal 84 specifying " end-of-characters " and which is employed to re-set the distributer 10. The signal thus produced by the matrix is then utilized to control the deflection waveform generator 12 comprising, as shown in Fig. 4, nine pulse generating circuits 54 (comprising, e.g. monostable multivibrators) having the input terminals 55-63 connected to the correspondingly numbered terminals of the matrix and producing, in response to the occurrence of an X and/or Y deflection pulse by the matrix, output pulses of the same duration t. The deflection waveform generator also includes six pulse-train generators 30 producing pulse trains having frequencies f2,f3,f5,f7,f8 and f10 each of which is fed to a respective shaper and splitter 32 providing two outputs of the same frequency but of opposite polarity. These pulse trains are then fed, selectively, to the X and Y deflection integrators 38 and 40 respectively via AND gates 34 and 36 in accordance with the pattern of second inputs to the gates from the generators 54 the polarity of the pulse trains passed to the integrators being determined by the presence or absence of inhibiting inputs to the gates from flip-flops 50, 52 controlled by the outputs on terminals 68 and 70 of the matrix and re-set via NOR gates 64 and 66 respectively. The outputs of the integrators, which produce ramp waveform output by integration of the input pulse trains, are then supplied to the X and Y deflection coils 46 and 48 respectively to cause the beam of the display tube 14 to trace the required character, portions of the trace not forming part of the character being blanked out by pulses from a generator controlled by the signal or terminal 92 of the matrix and supplied to the control grid of the tube. Fig. 2 shows the X-deflection waveform (2B) and the Y-deflection waveform (2F) which are utilized to produce the character A (2A) the pulse patterns controlling the generation of the waveforms being shown at 2C, 2D, 2E and 2G, 2H, 2I respectively. Representative segments of characters together with appropriate pulse frequencies for their generation are described in connection with Fig. 6 (not shown). Reference has been directed by the Comptroller to Specification 1,122,568.