Patent GB-1251689-A (GB)
IPC: G09G5/08
Filed: 1968-12-23
Abstract: 1,251,689. Cathode-ray tube displays. A. B. DICK CO. 23 Dec., 1968 [2 Jan., 1968], No. 61119/68. Heading H4T. In an arrangement for displaying Alpha- Numeric characters by selective brightening of the beam of a cathode-ray display tube during a conventional television-type line raster scan counter means responsive to vertical and horizontal sync. signals produces a succession of pairs of output signals specifying dot addresses in a two-dimensional matrix and from these signals the addresses of the dots which, when brightened, form desired characters, are derived for all of the characters to be displayed by means of respective sets of logic gates and supplied to respective selection gates activated under control of signals from a memory which stores signals indicative of each character at an addressable location to supply the character forming dot address signals of selected characters to the beam control electrode of the display tube when the beam is in the position at which the desired character is to be displayed. Fig. 1 shows the general arrangement and Fig. 2 shows details of the display control unit 10. As shown, horizontal and vertical sync. signals are derived via separator 22 from the sync. source 16 utilized for control of the display tube comprising a television monitor 57. The separated sync. signals are fed to counter control 32 which routs the horizontal sync. to start an 8 mc/s. clock 28 which supplies 384 pulses to an X Matrix Counter 34 during one line period and then stops until triggered by the next horizontal sync. pulse. The 384 pulses provide for 32 line segments each of 12 dot positions (see Fig. 5) of which 9 dots form the horizontal dimension of a matrix in which the characters are displayed and 3 dots provide characters spacing. At the end of each count of 12 counter 34 " overflows " and steps on Display Character Counter 24 by one count until the count reaches 32 (there being 32 characters in one line scan of the display tube) at which its " overflow " acts via control 32 to stop the clock 28. The vertical sync. signals are counted in Y Matrix Counter 36 which on reaching a count of 14, there being 11 dot position (line scans) in the vertical dimension of the matrix for character display and 3 dot position line scans for spacing, " overflows " into the Display Line Counter 26 to cause it to advance one count to a maximum of 16 (i.e. there are 16 lines of characters in a complete display field). The clock pulses counted by the X matrix 34 and the line pulses counted by the Y Matrix 36 are then utilized via logic gate circuits to produce, for all of the characters to be displayed, the actual beam control signals which when applied to the display tube, cause the desired character to be displayed. E.g. see Figs. 11 to 14 which show the logic circuitry associated with the characters L, T, the oblique / and the character N respectively. The character producing signals are then supplied to a video selector 30 (detailed in Figs. 15 and 16, not shown) in which the actual character which it is desired to display is selected and supplied via mixer to the display tube. Signals indicative of all the characters tc be displayed are stored in a core memory 40 at addressable locations the characters being derived from e.g. a tape reader 12 or a keyboard 14. The memory 40 is controlled by an address generator 67 which causes it to output to register 42 the signals indicative of a desired character when the address position of the beam of the display tube corresponds to the position of which the character is to be displayed. These signals are then decoded in 44 and employed to select the character in the selector 30. A flash control 46 may also be operated by a " non-viewable " signal output of memory 40 to produce a flashing at the horizontal sync. pulse rate of particular word to call attention to it. A " cursor " is also produced and under control of the keyboard and this cursor, which may be displayed, is moved to various positions identified by the count in counters 64, 66. When it is desired to enter character information in the memory 40 the cursor is shifted to the position corresponding to the desired address for the new information and the actual storage occurs when the cursor address corresponds to the address specified by counters 24 and 26. (For Figures see next page.)