Patent GB-1211948-A (GB)
Title: Crt curved character generator
IPC: G09G1/10
Filed: 1968-12-23
Abstract: 1,211,948. Cathode - ray tube displays. SPERRY RAND CORP. 23 Dec., 1968 [26 Dec., 1967], No. 60972/68. Addition to 1,108,401. Heading H4T. In an arrangement for tracing Alpha- Numeric characters on the screen of a cathoderay tube (CRT) under the control of digital signals derived from a character matrix, specific to a particular character, the matrix, in addition to providing signals indicative of successive X, Y co-ordinates defining the character and signals indicative of the beam intensity required for traces of different length to be produced with equal brightness, also provides signals indicative of a desired amount of and a desired direction of curvature for each segment of the character. The invention is described as applied to the Alpha-Numeric CRT display system of Specification 1,108,401 which is modified by the addition of curvature signalproducing elements in each character matrix and the provision of associated logic circuitry. Fig. 1 shows the general scheme in which the curvature signals C from the modified matrix are applied to logic circuitry 34 from which curve tracing signals are derived and combined with the normal X, Y deflection and intensity control signals I for control of the display on CRT 24. Fig. 3a shows the modified matrix comprising diode elements producing the X and Y co-ordinate signals and the intensity signals I required for producing the character B in the system of the above Specification together with additional diode elements producing signals C related to the required curvature and comprising signals MAG determining the magnitude of the curvature on output lines 94, 96 and signals determining the direction of the curve, R (right-hand) and L (lefthand) on output lines 98 and 100 respectively. Fig. 3b shows how the character B is traced when successive strobing pulses #1 ... # 8  are applied to the input lines of the matrix and Fig. 3c show the initial and terminal coordinates X, Y and X<SP>1</SP>, Y<SP>1</SP> respectively of each of the seven segments forming the character together with the relative intensity of each segment and the magnitude and direction of the two curved segments 3 and 6. Figs. 4a and 4b (arranged as shown in Fig. 4) show how the signal producing curves are derived. Referring to Fig. 4a, the signals on the output lines 94, 96, 98, 100 of the matrix of Fig. 3a (contained in cable 16) are decoded by the flip-flops 102, 108, 110 to produce signals indicative of direction on lines 124, 130, 132 and signals indicative of the actual deflection required to trace the curve on lines A to E inclusive. When a curve is to be traced an output is produced by either or both of flipflops 108, 110 (in the set condition) and such output(s) form, via OR gate 118, one input to AND gates 136 . . . 150 which receive as second inputs successive minor strobing, pulses #<SP>1</SP> 1  . . . #<SP>1</SP> 8  from a cycle of nine pulses (#<SP>1</SP> 9  serving merely to introduce a delay) which occur during the interval between successive ones of the (major) strobing pulses # 1  . . . # 8 . The outputs from the AND gates strobe the diode matrix to produce output signals on lines ABCD or E (depending on the particular curve to be drawn) which output signals, together with the magnitude and direction signals are utilized in the circuit of Fig. 4b, to produce on line 234 signals, which when supplied to the deflection circuit, cause the beam to trace a right-hand curve with the required magnitude. For tracing left-hand curves the AND gates 208 . . . 220 and the amplifiers 222 . . . 223 with their associated weighting resistors are duplicated and the outputs corresponding to right- and left-hand curves are supplied to the right and left sides of the push-pull X deflection circuit (Fig. 8, not shown). Typical right-hand curves (traced in a counter-clockwise direction) are shown in Figs. 5, 9 and 10.