Patent GB-1393653-A (GB)
Title: Display device with means for drawing vectors
IPC: G09G1/10
Filed: 1973-06-08
Abstract: 1393653 Cathode-ray tube displays DIGITAL EQUIPMENT CORP 8 June 1973 [8 June 1972] 27497/73 Heading H4T In a cathode-ray tube (or X-Y plotter) display arrangement in which lines (e.g. vectors), are drawn with reference to a rectangular co-ordinate system substantially constant trace intensity is maintained by making the trace velocity along the axis having the larger co-ordinate component substantially uniform and independent of the magnitude of such component. As shown in Fig. 2, co-ordinate deflection quantities #X, #Y are supplied by a data device 11 to an adder 34 and to respective shift registers 35, 36 which are shifted towards the most significant positions by pulses from clock 37 until a "1" is detected in a most significant position of either register at which occurrence such condition is effective via one of conductors 35a or 36a and NOR circuit 41 to disable gate 40 and disconnect the clock pulses. The contents of each register are supplied over busses 35b, 36b to a comparator 42 which operates to transfer the larger of the two deflection quantities #X or #Y to a D/A converter 62 and the larger of these quantities, after the shifting operation, to a D/A converter 43. The latter generates an analogue output voltage which varies inversely as the magnitude of the binary number (i.e. the larger of the #X #Y deflection quantities) input and this output voltage is integrated by the circuit arrangement including capacitor 45, resistor 46 control switch 47 and amplifier 48 to produce a linear ramp waveform having a slope proportional to the output from D/A converter 43. The ramp waveform provides an analogue input to multiplying digital-to-analogue converters 50, 51 which have as second inputs the normalized (shifted) quantities from respective shift registers 35, 36 and produce respective outputs equal to the product of the slope of the ramps and the respective inputs from registers 35, 36. Thus, the slope of the ramp output from the converter 50 or 51 to which the larger of the shift register outputs is supplied is constant and independent of the slope of the ramp output from amplifier 48 and thus the slopes of the outputs from converters 50, 51 are related by the ratio #X/#Y and thus the velocity components are in the same ratio. The output of the converters 50, 51 are then supplied to summing circuits 57, 61 via switches 58, 60 which respond to inputs from the converters to cause the summing circuits to "add" or "subtract" the component axes deflection inputs in accordance with the required direction of deflection. The larger of the #X, #Y deflection quantities fed to D/A converter 62 from comparator 42 before the shifting operation is compared in comparator 63 with the larger of the outputs from the converters 50, 51 by means of a switch 64 so that when the two inputs become equal (when the beam reaches the end of the major axis deflection), the tube beam is blanked and switch 47 is closed to prevent further integrator action. The actual component deflections commence from the existing beam positions defined by the quantities in X and Y registers 53, 54 and these are up-dated by means of X and Y position registers 65, 66.