Patent GB-1109441-A (GB)
Title: Improvements in or relating to data display apparatus
Inventor: MACDONALD JOHN BURNET
IPC: G09G1/10
Filed: 1964-05-13
Abstract: 1,109,441. Cathode-ray tube displays. MARCONI CO. Ltd. 18 Feb., 1965 [13 May, 1964], No. 20006/64. Heading H4T. In an arrangement for displaying data on a cathode-ray tube by a trace made up of a series of lines between successive points each representative of the value of a different item, each line is traced at the same speed, as measured along the trace, so that the latter is of constant brightness. The data comprising e.g. the voltage output of a number of thermopiles distributed throughout a nuclear reactor, is supplied via individual lines A 1  . . . A M  to a sampler B supplying each input in turn to an analogue-to-digital converter C. The digital " words " set-up in the latter are subsequently employed to determine the Y co-ordinate position of the commencement of each line trace against an X co-ordinate time-base deflection position determined by the digital " words" derived from a digital signal generator C<SP>1</SP>, consisting of a periodic staircase generator feeding an analogue-to-digital converter, the staircase generator having a repetition frequency equal to the sampling frequency and a number of steps equal to the number of bits in the digital " word " produced by C. The outputs from C, C<SP>1</SP> are fed to subtractor register D, D<SP>1</SP> which supply outputs representative, respectively, of the difference between successive Y and X values to registers E, E<SP>1</SP> feeding respective shift register F, F<SP>1</SP>. The latter, which feedback to the input sides of register E, E<SP>1</SP>, are controlled by the output of an OR gate G supplied with respective inputs from the most significant section of the registers E, E<SP>1</SP>, the output of gate G operating the shift registers F, F<SP>1</SP> to shift the " word " in E, E<SP>1</SP> towards the most significant position until a " 1" appears in this position in either or both registers E, E<SP>1</SP> at which the shifting is ousted. The number of shifts necessary to achieve this condition is counted by a counter H the output of which is fed to a selector J, having a number of outputs (determined by the number of " bits " in the " words " in the registers) controlling respective gates Lo, L1 . . . &c., to which are supplied the outputs of respective ones of a chain of ¸ 2 frequency dividers N supplied from a square wave source M of a suitable high frequency. In accordance with the count (if other than zero) effected by H, one or other of the gates Lo, L1 . . . &c., are energized and supply the square wave output of their associated divider(s) N to the brightness control electrode of the display tube K. Since the count effected by H is determined by the magnitude of the difference Y2-Y1 or X2- X1 (whichever is the greater), on which the slope and length of each line to be traced also depends, the latter determines the duration of the bright-up pulse which comprises the halfwave of appropriate polarity of the output from the particular gate Lo, L1 . . . &c., which is opened. The leading edge of the bright-up pulse is employed to trigger sawtooth generators S, S which produce sawtooth voltage waves having a slope determined by the " words " in respective registers E, E<SP>1</SP>. These waves which determine the slope and length of the line to be traced, are combined in respective adder R, R<SP>1</SP>, with voltages determining the endpoint of the last trace, such being derived by supplying the " words " in registers C, C<SP>1</SP> via scan period delay units P, P<SP>1</SP> and digital-toanalogue converters Q, Q<SP>1</SP> to the adders R, R<SP>1</SP>. The outputs of the latter are then fed via respective amplifiers T, T<SP>1</SP> to the Y and X deflection means of the tube to produce the required trace. This terminates with the end (the trailing edge) of the bright-up pulse which is utilized to re-set the counter H and the registers D, D<SP>1</SP> and to return the sawtooth generators S, S<SP>1</SP> to a datum position. The trailing edge may also be employed to condition the sampler B and the units C, C<SP>1</SP> for operation in respect of the coordinates of a further point. The arrangement of the invention thus operates to trace all lines of the same speed independently of their length so that, since the beam is held at constant intensity, all lines traced are of uniform brightness.