Patent GB-1175377-A (GB)
Title: Dataphone Driven Remote Display System.
IPC: G09G1/10
Filed: 1966-12-19
Abstract: 1,175,377. Cathode ray tube displays. RANK ZEROX Ltd. 19 Dec., 1966 [27 Dec., 1965], No. 56669/66. Heading H4T. [Also in Division G1] A data display system in two-way communication with a digital computer has facilities for (1), controlling the deflection of the beam of a cathode-ray display tube to trace vectors having co-ordinates determined by digital signals received from the computer, (2) controlling the bright-up of the beam, when it is scanned in a fixed pattern to display Alpha-Numeric, &c. characters determined by digital signals from the computer or from a keyboard associated with the display system and which may also be employed to interrogate the computer and (3) recording the vector display and if desired, the Alpha-Numeric display, using an xerographic technique and optically projecting the recorded display for viewing by the operator. For the production of Alpha-Numeric characters a selection switch 20 (Fig. 1), is operated to initiate a "load" mode of operation in which a circulating delay line 43 (also Fig. 2, not shown) is loaded via logic circuit 47 under the cantrol of digital signals from the computer indicative of, in addition to synchronizing functions, the complete font of characters utilized, or in a section of line 43 termed "prelook", with digital signals from the keyboard 21 indicative of desired characters. The signals from the computer comprise successive 10 bit words of which the first word controls the routing (e.g. to the load logic 41, the write logic 42, the vector pattern generator 71 or the xerographic developing control unit 15). In the case of Alpha-Numeric display operation 7 bits of the subsequent words specify the particular character which, by means of the load logic 41 are converted to a serial stream of 84 bits one of each of which is inserted in a different one of 84 serial spaced groups of bits, the position (order) of each bit of the 84 defining a particular character being the same in each group and indicative, according to a known code (ASC 11), of that character. In a second operational mode, termed the "write" mode, digital signals from the computer, if indicative of Alpha-Numeric characters, are compared in a counter in write logic 42 with the count of the bits circulating in the delay line and on the occurrence of a match, which occurs once in every group of bits, such bit is gated out and if a "1" utilized to bright-up the beam of the display tube 61 the scanning of which is effected in a fixed pattern (Fig. 3, not shown) by means of character generator 72 and X and Y deflection amplifiers 81, 82 under the control of logic circuit 42. When, in the "write" mode, the signals from the computer are indicative of line graphics (e.g. vectors) such signals, comprising digital information representing, with respect to an initial, previously determined, position, the sign and magnitude of the increments #X, #Y required to trace the vector, are routed via buffer 70 to the vector generator 71. This includes, as shown in Fig. 4, registers 107, 108 coupled to digital-to-analog converters 109, 110 which supply reference voltages to a second set of digital-to-analog converters 111, 112 connected in parallel with an 8 bit counter 150 the count of which is initiated after both the #X and #Y "words" have been entered into the registers 107, 108 respectively. The outputs of the converters are thus increased by one increment for every count of counter 150 and since the reference voltage fed to 111, 112 is scaled by #X, #Y the change in output voltage is directly proportional to the magnitude of #X, #Y. Such outputs are then summed with the outputs of the initial X, Y position digitalto-analog converters 103, 104 in networks 105, 106 and fed to the X and Y deflection amplifiers 81, 82 (Fig. 1) respectively so that the tube beam is deflected to its new position in a series of discrete and equal linear steps. After the 255th count of counter 150 the beam is blanked and the logic circuitry then operates to add or subtract, depending on the sign, the #X and #Y quantities to or from the initial position information in counters 101, 102 and to condition the system to accept a new quantity #X, #Y. Since, in operation, the rate of movement of the tube beam is directly proportional to the length of the vector traced, uniformity of trace brightness is achieved by utilizing the outputs of the converters 109, 110, after summation in network 170, to control the beam intensity. For display of the data the tube 61 (Fig. 5) utilizes a phosphor producing light with a long decay time in the yellow region of the spectrum and light with a short decay time in the blue region. The latter (blue) component is directed via a dichroic 70, virtual image viewer 60 and lens system 64 to an xerographic plate 62 and the former (yellow) component is directed via 70 and 60 towards the viewing window. During the production of data on the tube screen the plate 62, which is held in a cassette 68, is maintained normal to the optical axis of lens 64. When the charge pattern has been "laid-down" a signal from the computer operates via unit 15 (Fig. 1) to energize a motor 681 which effects a rocking motion of the cassette and causes "developer particles" contained in one end of the latter (see Fig. 9A, B, C, not shown) to be spread over plate 62. The cassette is then brought to rest at an angle of about 30 degrees to the horizontal (see Fig. 6) and light from a source 640 which falls obliquely on plate 62 is specularly reflected towards the viewing window via the appropriate optical elements shown. Since the "developer particles" which adhere only to the charged image areas, produce scattering of the incident light the image resulting from the specularly reflected light is produced as a black trace on a white background. When it is desired to erase the image a signal from unit 15 (Fig. 1) causes the plate 62 to be flooded with light and simultaneously causes the cassette to be rocked (similarly to the rocking motion used for development) so that the cascading "developer" frictionally effects full erasure of the charged areas. Because of the recording effected by the latter process a single non-recurring trace need only be produced on the tube screen but, at the will of the operator, the trace may be repeated. Traces which are to be recorded are produced on a predetermined area of the tube screen-a square area. Other traces, e.g. in a "pre-look" mode of operation when the operator may wish to view data before deciding if it is necessary to record it, are produced in a single line outside the area reserved for recording. The system only allows such data to be presented at a rate of 2À5 frames per second and hence, to avoid undesirable flicker only the long decoy time yellow light is directed towards the viewing window by means of the dichroic 70 (Fig. 5). Instead of employing the xerographic recording arrangement, the display tube may be of the storage type and viewed directly.