Patent GB-1285539-A (GB)
Title: Improvements in and relating to electrical signal representation
IPC: G01R13/34
Filed: 1971-04-19
Abstract: 1285539 Cathode-ray tube displays SOUTH AFRICAN INVENTIONS DEVELOPMENT CORP 19 April 1971 [20 March 1970] 24743/71 Heading H4T A time variable function at input 17 to be continually displayed on a cathode-ray tube 23 is converted to digital form in an analogue-todigital converter 18 and is stored in a memory 1, continual updating of the stored information being effected in discrete steps by storing a new digital word of function information and at the same time releasing from the memory 1 the oldest digital function information word therein. The stored information is repetitively read out at a higher rate than that at which updating occurs and is displayed along a time axis on the C.R.T. 23. The display of the function is shifted progressively across the display screen in steps corresponding to each updating of the stored information, new information introduced to the memory 1 at each updating being added at one side of the screen while the released oldest stored information leaves the opposite side of the screen. In the embodiment shown the memory 1 recirculates the stored information via line 20 and the full-line position 19a of gate 19. Readout of the recirculating information occurs via digital-to analogue converter 21 and linear interpolator 22. A master clock circuit 12 feeds pulses 11 on line 24 to control shifting of the stored information through the N storage positions la of the memory 1, and also supplies the pulses 11 to a control circuit 9. This circuit normally passes these pulses directly to a divider 14, which generates a pulse 15 for every N input pulses. However, when a periodic update command 10 is given to control circuit 9 on line 29, one of the pulses 11 is inhibited, producing a pulse train 13 and resulting in delay of the pulse 15 by one clock pulse. The pulses 15 are used on line 26 to initiate sweeping of a time base voltage in C.R.T. 23 and on line 27 to switch the gate 19 to the broken line position. The effect of delaying the pulse 15 by one clock pulse is to introduce a new digital function information word to the memory 1 and to erase the oldest stored word. The delay also causes the necessary phase change which moves the displayed function bodily across the screen of the C.R.T. 23. In the absence of an update command 10 the recirculating information remains unchanged and the display is "frozen". In a modification (Fig. 3, not shown) the memory (1) includes a single storage position (1b) which is separated from the remaining N storage positions (1a) by a gating arrangement (30) which normally allows all the stored digital words to recirculate through the entire memory (1) including the separate storage position (1b) but which, on receipt of an update command on line (36), isolates the oldest stored word in the position (1b) for N - 1 information transfer steps, permits recirculation of words stored in the remaining positions (1a), and introduces a new digital word representing an updating of the stored function information. On release from the separate storage position (1b) the oldest stored word is lost from the memory (1) due to the adverse setting of the gate (19) at that moment. If a plurality of functions are to be displayed n storage positions of the memory for each function are arranged serially to provide N positions in all. The sweeps of the display time base for the various functions are initiated cyclically.