Patent GB-1423682-A (GB)
Title: Display generators
IPC: G01S7/14
Filed: 1973-04-27
Abstract: 1423682 Cathode-ray tube displays LITTON INDUSTRIES Inc 27 April 1973 [27 April 1972] 20250/73 Heading H4T In a cathode-ray tube (vector) display system the rate of beam deflection along the X and Y co-ordinate axes is made proportional to the X and Y co-ordinates of the vector. As shown in Fig. 1, line length counter 10 is supplied with data specifying the length of the line (vector) to be traced and a line rate controller 19, comprising a binary multiplier supplied with clock pulses and with data specifying a basic deflection rate produces pulses at this rate which count line length counter 10 down to zero thus supplying a succession of pulses to X and Y rate multipliers 16, 24 which also receive the basic rate pulses from controller 19. The multipliers 16, 24 are also supplied with X and Y co-ordinate data including a sign bit, and produce pulse train outputs on lines 27, 40 having a duration determined by the length data supplied to counter 10 and respective rates determined by the X and Y axes component data and in addition supply the sign bit outputs on lines 30 and 43. The outputs on lines 27 and 40 are fed to respective "OFF SET" counters 28, 41 and to respective display bit counters 29, 42 whilst the outputs on lines 30 and 43 are fed to the respective "OFF SET" counters 28, 41 and via exclusive OR gates 31, 44, to the respective display bit counters 29, 42. Additionally the "OFF SET" counters are loaded with data specifying positions at which no display is to be produced, e.g. screen limits and off screen positions in which the start of a vector may occur and the display bit counters are loaded with data specifying the X and Y co-ordinates of the start position of a vector. In operation, the display bit counters 29, 42 are counted up or down, depending on the sign bit, at respective rates determined by the X and Y co-ordinates of the end point of the vector and the outputs of the counters are converted to analogue form in D/A converters 37, 53 and supplied to the X and Y deflection circuits. When the length of the vector is such that it would extend beyond an edge of the display screen the display bit counters 29 and/or 42, on reaching counts indicative of the screen limits, supply outputs on lines 36, 50 which advance the count in OFF SET counters 28, 41 and the latter then supply a beam blanking signal on lines 39, 55 and a sign change bit on lines 33, 46 which act via OR gates 31, 44 to change the direction of counting of the display bit counters 29, 42. Thus the display of a vector such as 62 (Fig. 4), which would extend beyond the sight band edge of the screen at 63 is effectively "reflected" along path 64 and when this tends to extend beyond the top screen limit is again effectively "reflected" along path 65, the beam being blanked during the deflection along these paths. Instead of presetting a line length in counter 10 signals derived from a radar scan may be supplied and if the resulting trace would exceed the screen limits the operation of Fig. 4 results or, if only a portion of the trace is to be displayed so that, e.g. the trace effectively commences "off screen" as at 66 (Fig. 5) and the portion which it is desired to display commences at point 69 (in the screen area 56), the OFF SET counters, here assumed to be three bit counters, are loaded with the indicated X and Y data (the sign change, i.e. direction of counting, being determined by a change in the least significant bit) and the operation then follows that described in connection with Fig. 4. Fig. 6, shows an Alpha-Numeric character generator in which the strokes forming the characters, e.g. N (Fig. 7) and K (Fig. 8) are produced by up-down counting of counters 88, 89 the outputs of the counters being converted to analogue form in D/A converters 90, 92 and supplied to the X and Y deflection circuits. The characters so produced may be displayed along a vector produced by the arrangement of Fig. 1 by summing the signals on lines 38 and 91 and the signals on lines 54 and 93.