Patent GB-1004574-A (GB)
Title: Improvements in or relating to information display systems
Inventor: ROGERS MARK ANTHONY MEYRICK
IPC: G09G1/18
Filed: 1962-08-31
Abstract: 1,004,574. Selective signalling. INTERNATIONAL SYSTEMS CONTROL Ltd. Aug. 30, 1963 [Aug. 31, 1962], No. 33574/62. Heading G4H. [Also in Division H4] An alpha-numeric display system comprises a magnetic drum store 1 having a track 7 including a plurality of portions in each of which can be stored a coded representation of a character of the information to be displayed, and having associated with it a reading head 8 and a writing hand 9; a cathode-ray tube 6 at least part of the area of the screen of which may be considered as being made up of a series of elements, each of which is capable of having reproduced on it one character of the information to be displayed, and a scanning control circuit 10 adapted to apply scanning signals in operation to the beam deflecting means 11 of the cathode-ray tube so as to cause the electron beam of the cathode-ray tube repeatedly to scan said elements in sequence, line by line, in a series of frames, each frame representing a complete scanning sequence of all the elements of the screen 5. To ensure that during a display period, that is, a period for which information stored in the display track 7 is being displayed, the scanning of the elements of the screen 5 is appropriately synchronized with the reading of the stored information, the drum store 1 has a clock track 12 in which is stored information representing one or more synchronizing signals. Each scanning sequence is performed in a series of steps corresponding in number to the number of elements of the screen 5; each step consists of a period of 12 microseconds (dwell time), during which in the absence of any character generating signal applied to the beam deflecting means 11 and provided that the electron beam is not effectively cut off, the beam dwells on a central portion of the relevant element, and a period of 3 microseconds during which the beam is switched from this element to the next element in the series. The display system also includes a character generating unit 15 which comprises a plurality of electric circuits, each of which produces, in response to an appropriate input signal, a modulated signal which during the swell time of one step of a scanning sequence, causes the beam to trace out a particular character. A decoder 16 includes a shift register 17 which is arranged to store each set of six digits representing a coded character as the corresponding signals are applied to it from the reading head 8. Each set of six digits is fed to a staticizer 18 where it is held while the character generator unit 15 generates a corresponding modulated signal and the next set of six digits is accumulated in the shift register 17. For each revolution of the drum store particular characters are reproduced on the same corresponding elements of the screen and as the drum rotates at 60 revolutions per second the display is steady and free from flicker. The operation of the shift register 17 and staticizer 18 are synchronized with the reading of stored information from track 7 and with the scanning of screen 5 by means of further synchronizing signals developed in the timing circuit 14 in response to signals developed from the clock track 12. The brilliance control electrode not) shown) of the cathode-ray tube is linked with character generating unit 15 so that if a storage portion has no coded character stored in it the electron beam is cut off. Information from data processing circuits 4 may be written into some or all of the storage portions of track 7 by means of writing head 9, and the information may be repeated one or more times around the circumference of the same display track, thus enabling the drum to be rotated at a lower frequency and still produce a steady display. In an alternative arrangement, each element of the screen of the cathode-ray tube is scanned in a series of a few parallel lines during the dwell time of the appropriate steps of each scanning sequence of the screen as a whole, the character generating unit being adapted to apply modulating signals to the brilliance control circuit of the cathoderay tube. In a further embodiment (Fig. 2, not shown) several information display systems each having a separate cathode-ray tube are incorporated in a data processing system having a single magnetic drum store, the information being stored in one or more tracks; switching means being provided for appropriately switching the output of the character generating unit from one to another of the cathode-ray tubes of the display systems.