| 摘要 |
1,086,699. Cathode-ray tube circuits. INTERNATIONAL BUSINESS MACHINES CORPORATION. Dec.15, 1965 [Dec.31, 1964], No. 53161/65. Heading H4T. The beam of a cathode-ray tube 26 (Fig. 1) is constrained to follow movement of a " lightpen " 25 over the tube screen by means of an arrangement in which a predetermined pattern of position defining spots (a), Fig. 6, produced on the screen is sensed by the " light-pen " which, when it senses at least one but not all of the spots, operates via control means to alter the position of the pattern in a direction such that all spots are sensed. If all spots or no spots are sensed no position alteration is effected and if the centre spot of the pattern is amongst those sensed-the sensing area of the " light-pen " being indicated by the circle of Figs. 6(a) . . . 6(f)-a smaller position alteration is effected than if the centre spot is not sensed. The spot pattern is produced by a circuit 46 (detailed in Fig. 4, not shown) which, under the control of pulses from a distributer 21, generates digital signals representative of the X and Y co-ordinates of the spots in a predetermined repeating sequence and these are then converted to analogue form in 47, 49 and supplied to a first deflection yoke 51. The sequence in which the spots are generated is also " set-up " in comparator/control circuit 23 and there compared with the signals sensed by the " light-pen "-supplied via amplifier 27 and lead 29-the result of the comparison being to provide signals which step-on a low order stage of X and Y position registers 31, 33 if the centre spot has been sensed or a high order stage if this spot was not sensed. The amount of beam deflection required is thus determined by the presence or absence of the centre spot from the light-pen and the outputs of the registers are then converted to analogue form in decoders 35, 37 and supplied to a second deflection yoke 45. Instead of a pattern of spots a pattern comprising a broken rectangle with a central dot may be employed (Fig. 6b). |
