Patent GB-1150208-A (GB)
Title: Display Apparatus.
IPC: G09G1/10
Filed: 1966-09-19
Abstract: 1,150,208. Cathode-ray tube displays. BUNKER-RAMO CORP. 19 Sept., 1966 [20 Sept., 1965], No. 41662/66. Heading H4T. In an Alpha-Numeric type symbol display system the production of each symbol is controlled by input data representative of a plurality of successive X, Y co-ordinate points defining the symbol, the system operating by deflecting a writing element with respect to a target on which a visible image of the symbol is formed at such a rate that the movement time between each co-ordinate point exceeds it dwell time at each point. In the embodiments described the display device comprises a cathode-ray tube but it is stated that the invention is applicable to other X-Y deflection systems such as a stylus moving over a piece of paper. The invention utilizes a known type of character generator (Fig. la) producing in accordance with input data fed to register 12, sequences of X-Y deflection control signals together with appropriate Z (unblank or brightup) signals for producing the symbols in a 15 x 15 dot matrix display on cathode-ray tube 10. To improve such a display-which comprises separate unconnected dots (Fig. 1b, not shown) the (step-like) input to each deflection amplifier 16, 18 is supplied via a delay line 60 (Fig. 3) also Fig. 2a (not shown), which smooths each input step and causes the beam to be deflected comparatively slowly between each defined co-ordinate point and in order to make such trace visible the blanking of the beam between successive Z signals is prevented by means of a set-reset flip-flop 70 which holds unblank generator 20 operative until the occurrence of an end of symbol output from 36. When a symbol containing a discontinuity, e.g. the symbol , is to be drawn the large step in the deflection signals operates via differentiation circuits 100, 102 (Fig. 5) and respective threshold level circuit 104, 106 to re-set flip-flop 70 so that the beam is blanked during such step. By suitably modifying the delay lines the symbols may be traced in smooth curves (Fig. 7a, not shown) instead of in straight lines and angles (Fig. 6a, not shown). Since the velocity of movement of the beam varies throughout each curve constant brightness is achieved by controlling the beam intensity in accordance with the slope of the deflection signals as determined by differentiation circuits 121. In another arrangement for introducing discontinuities-e.g. in order to blank the beam where the beam must retrace an already traced symbol element-the co-ordinates of an "illegal" point are inserted in the symbol defining data, e.g. X=13, Y=13, and a comparator circuit responsive to the occurrence of such steps operates via a monostable multivibrator to hold the beam blanked for a predetermined number of subsequent image points (Figs. 8a and 9, not shown). In a further arrangement for introducing discontinuities the beam blanking is controlled by providing a circuit in each symbol output line of the decoder 22 (Fig. 1a) and connecting each to predetermined ones of the outputs of counter 32 which operates the entire character generator (Fig. 10a, not shown).