GB1187556A - Signal Translator - Google Patents

Abstract

1,187,556. Cathode-ray tube displays. R.C.A. CORPORATION. 22 March, 1968 [12 April, 1967], No. 13900/68. Heading H4T. In an arrangement for producing graphical and alpha-numeric symbols on the screen of a cathode-ray tube some of the bits defining a symbol control the counting directions of a pair of bi-directional counters which count clock pulses and provide X and Y beam deflection signals, others of the bits pre-set a further counter which then counts down to zero under the control of clock pulses to provide a signal determining the length of the trace, a further bit controls the beam blanking and all of the bits control the overall operation of the system e.g. to produce a trace or to clear the system preparatory to receiving another symboldefining digital-word. Thus, as shown, the first three bits of a seven bit word in register 3 are decoded in Direction Decoder 5 and provide outputs L (left), R (right), U (up) and D (down) controlling the direction of counting of X and Y position counters 10 and 13 respectively. These counters, the outputs of which are converted to analogue form in converters 15, 17 and supplied to the X and Y deflection amplifiers 20, 22, count pulses, supplied via gates 13, 14 from a clock 12. When a symbol is to be traced the " Operation " output of a function decoder 25 supplied with all seven bits from register 3 " sets " a flip-flop 31 and the " 1 " output of the latter opens gates 13, 14 to pass the clock pulses to the counters 10, 11. The " 1 " output of flip-flop 31 also opens a gate 35 which then passes the last three bits of the word in register 7 to a length counter 36 which is preset thereby to a number indicative of the length of the trace and additionally the " 1 " output of 31 conditions a gate 40 to pass the middle bit of the word in register 7 to the beam intensity control 42 on the occurrence of a clock pulse. Length counter 36 is then stepped down on the occurrence of each clock pulse and when zero count is reached the output of 36 re-sets flipflop 31 so that gates 13 and 14 close and the beam deflection is terminated and gates 35 and 40 close and register 7 is cleared via OR gate 32. If the next digital word supplied to register 7 also indicates an " Operation " e.g. a continuation of the trace just produced, the cycle described is repeated. If, however, the next word indicates a clearance of the system preparatory to tracing a new symbol, function decoder 25 provides an " instruction " output which sets a flip-flop 30 the " 1 " output of which resets the X and Y position counters, clears register 7 via OR gate 32 and clears the display, by means not shown, via terminal 33. All symbols are traced as a series of spaced bright dots by the action of the clock pulses and the bright-up bit but the operation may be modified to produce a continuous trace. The CRT means 21 may include a storage scan converter tube producing output signals suitable for use by standard television receivers.