US3894292A - Display apparatus - Google Patents

Display apparatus Download PDF

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Publication number
US3894292A
US3894292A US338842A US33884273A US3894292A US 3894292 A US3894292 A US 3894292A US 338842 A US338842 A US 338842A US 33884273 A US33884273 A US 33884273A US 3894292 A US3894292 A US 3894292A
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United States
Prior art keywords
output
counter
raster
digital
delay
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Expired - Lifetime
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US338842A
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English (en)
Inventor
Brian Wilkinson
David John Jibb
Martin Neil Smith
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Allard Way Holdings Ltd
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Elliott Brothers London Ltd
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R13/00—Arrangements for displaying electric variables or waveforms
    • G01R13/20—Cathode-ray oscilloscopes
    • G01R13/22—Circuits therefor
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G5/00—Control arrangements or circuits for visual indicators common to cathode-ray tube indicators and other visual indicators
    • G09G5/20—Function-generator circuits, e.g. circle generators line or curve smoothing circuits

Definitions

  • G08b 5/36 each raster line notionally divide each line into a Field Of Search 340/324 AD; 315/22 number of equal ng h s q n i y n mber se tions changes in the brightness being effected when 1[56] References Ci there is correspondence between the digital output UNITED STATES PATENTS and the counter 3.388.391 6/1968 Clark 340/324 AD X 8 Claims, 7 Drawing Figures FATE-1 mm SHEET Cyclic A2 )4 Counter i0 H ⁇ v Delay B Compul'er ulpur dam Q 7 M Pulse Shaping Fig.2
  • This invention relates to display apparatus of the kind in which a display area is scanned in a raster and in which a symbol can be produced on the display area by causing a change in a visual parameter, e.g., brightness, of one or more selected portions of the raster lines.
  • a visual parameter e.g., brightness
  • this invention provides display apparatus of the kind hereinbefore defined comprising means for producing a digital output defining the position of each raster line portion required to be selected to display a desired symbol, means for producing reference signals corresponding to points along each raster line and an output circuit for producing a signal for changing said visual parameter at each selected raster line portion determined by the digital output.
  • the display apparatus includes a cyclic counter operating in synchronism with the raster line scanning generator such that a large number of pulses occur during each raster line, thereby notionally dividing each raster line into a large number of equal length, sequentially numbered, sections changes in said visual parameter being effected when there is correspondence between the digital output and the output of said counter.
  • the display apparatus includes at least one delay circuit for delaymg the signal from the output circuit whereby the number of sections into which each raster line is divided is effectively increased without increasing the pulse frequency from the cyclic counter.
  • the display apparatus includes a circuit for changing the shape of the signal from the output circuit whereby the number of raster lines is effectively increased
  • FIG. 1 is a schematic diagram of a cathode ray tube screen showing the parameters defining a line symbol
  • FIG. 2 is a block diagram of the display apparatus
  • FIG. 3 is a block diagram of the output stage of FIG. 2:
  • FIG. 4 is a block diagram of the delay circuit of FIG. 2;
  • FIGS. 5a and 5b show respectively the optimum and actual shapes of bright-up pulses applied to the cathode ray tube under certain conditions of operation of the apparatus.
  • FIG. 6 is a block diagram of the pulse shaping circuit of FIG. 2.
  • FIG. 1 a line symbol 1 l5 shown displayed on the screen 2 of a cathode ray tube.
  • the screen is scanned by an interlaced field raster having even field lines 3 and odd field lines 3a.
  • the raster may be a 625 line, 50 Hz, raster, but for the sake of simplicity FIG. 1 shows a 12 line raster.
  • the line symbol is made up of a series of brightened-up portions of the raster line. These brightened-up portions are produced by applying bright-up pulses to the brightness control circuitry of the cathode ray tube. For each brightened-up portion, it is necessary therefore to determine on which line of the raster the brightened-up portion is to occur (Y-co-ordinates) and at which points on the raster line the brightened-up portions are to begin and end (X-coordinates).
  • the X co-ordinates for successive brightened-up portions increase by thesame amount each time. This amount is called the increment and is equal to h tan 6 where h is the spacing between the raster lines.
  • the values of Xst and Xop for the first line of the odd field can be found and values of Xst and Xop for succeeding lines of the odd field can be found by successively adding twice the increment to the values of Xst and Xop for the first line of the odd field.
  • the increment is zero whereas at 0 45 the increment is equal to h. If the raster lines are considered to have unit spacing then at 6 45 the increment is 1. In this case the increment must, be fractional for lines having 6 between 0 and 45, which implies that Xst and Xop must contain a fractional part. Since, from equations (2) Xop Xs! w sec 6 this fractional part must be the same for successive values of X5! and Xop. Therefore. if the increment is split into two words inc and inc frac, each of bits. lines having these angles can be drawn.
  • inc frac On each line inc frac is added to X frac and inc is added to X51 and Xop. On the line where X frac overflows the carry is added to Xsr and Xop.
  • the binary output from the computer is fed to and stored in an output circuit 11 which is also fed by pulses from a cycle counter 12 in synchronism with the line scan.
  • the cyclic counter 12 provides the division of the raster lines into X coordinate sections. To provide 780 sections per raster line, the frequency of the pulses must be 780X( 1/52) US which equals MHz. (52 US is the time of line scan).
  • Coincidence between Xst and Xop and the relevant clock pulses causes the generation of a bright-up pulse which is fed to the brightness control of a cathode ray tube 13 through a delay circuit 14 and a pulse shaping circuit 15 or through the delay circuit 14 alone depending on the value of 0 as explained below.
  • the actual output therefrom involves only the current values of Xsl and Xop. As shown in FIG. 3 these values are stored in respective output registers l6, 17. Each register has an associated comparator l8, 19 so that the value of Xst and Xop can be compared with the count from the cyclic counter 12. The outputs from the comparators l8, 19 are fed to a gate circuitry 20 which in response to the outputs develops a signal during the period when the output from the counter 12 is 2 X5! and s Xop.
  • the stepped appearance of a near vertical line is due to the X position being limited by the number of steps along the raster line provided by the cyclic counter 12.
  • the steps are most apparent when the increment is zero and inc frac is non-zero, i.e., at the point when X frac is carried over and Xst and Xop shift by one place which is approximately a 60ns shift.
  • the X definition needs to be increased and the pulses shifted according to X-frac. This could be done by increasing the pulse frequency but 15 MHz is the practical limit using standard components.
  • the solution adopted is to use delay circuitry and select the delay according to the value of X-frac.
  • To increase the X-definition by a factor of 4 three 15 ns delay circuits 21, 22, 23 are used as shown in FIG. 4.
  • the outputs from the delay circuits are fed to a 4/1 multiplexer 24.
  • the two most significant bits of X frac are applied by way of line 24a to data select lines of the multiplexer to select an appropriate delay.
  • n delay circuits each having a delay x, and an (n l)/l multiplexer can be used, provided that (n 1 )x equals the cyclic counter pulse length.
  • the use of the delay technique means that the pulse frequency can be reduced if required, without losing the original definition. For example, seven 15 ns delay circuits and a frequency of 7 /2 MHz gives an effective frequency of 60 MHz which is the same as if three 15 ns delay circuits and a 15 MHZ frequency are used.
  • Such a reduction in the pulse frequency has definite advantages particularly with regard to the output stage where Xst and Xop are compared with the output of the cyclic counter. As there is a reduction in the number of bits to be compared, a significant reduction in the amount of hardware is produced.
  • the length of the bright-up pulse must vary.
  • the increase in length of the sections defined by the cyclic counter at a reduced frequency means that the actual length of the bright-up pulse may not be the same as the right length to give a constant width line symbol.
  • a differential delay factor must be introduced; i.e., a brightup pulse is delayed by different amounts at its rising and falling edges.
  • a 2/1 multiplexer 50 shown dotted
  • the integer bits are fewer and accordingly, no penalty is incurred as regards storage requirements.
  • FIG. 5A shows the optimum shape of the bright-up pulse.
  • FIG. 6 shows the leading and trailing edges of the pulse.
  • the pulse shaping circuit of FIG. 6 consists of a bi nary rate multiplier (BRM) fed by pulses from the cyclic counter and having its output connected to the input of an up-down counter 26.
  • Output signals from the counter 26 on lines 30-32 are fed to a l of 8 decoder 33.
  • the output from the decoder 33 is fed to an non-linear digital to analogue converter 34 which has a non-linear characteristic of such terms as to control the bright-up circuitry of the tube so as to provide visually acceptable symbols.
  • the BRM 25 is a device which performs the function frequency in X M frequency out where M is a 6 bit number in the range 0-63.
  • the frequency out is in fact a pulse rate which can be made repeatable using the clear facility on the BRM.
  • the up-down counter 26 is fed by the frequency out and counts at a rate determined by the frequency out.
  • the counter 26 begins counting at the beginning of the bright-up pulse, i.e., at Xst. The counting stops after seven counts and when Xop is reached the counter begins counting down to zero.
  • the final output from the converter 34, which is applied to the brightness control is a pulse having leading and trailing edges formed of eight steps. The brightened-up portions of the raster thus have a brightness varying through eight shades of grey.
  • the control circuitry from the BRM 25 and the counter 26 consists of gates, A, B and C.
  • the gates-A, B receive the outputs from the output circuit gate 20 (FIG. 3) and from the lines 30-32 of the counter.
  • the outputs from gates A and B form the input to gate C which has its output connected to the clear-enable facility of the BRM. Considering the output from the counter to be initially zero, the sequence of events is as follows:
  • the gate A is enabled thus enabling the gate C and the BRM and the counter.
  • the gate B is inhibited, thus inhibiting the gate C and clearing the BRM.
  • the gate B is enabled, thus enabling the gate C and the BRM and the counter again with the counter in the count-down state.
  • the gage A is inhibited, thus inhibiting the gate C and clearing the BRM.
  • the technique described above only allows the use of graded bright-up pulses over angles of 0 +77 to and -77 to 90". Outside these angles the appearance of the line is degraded. To overcome this, the influence of the BRM is extended by reducing the number of shades of grey to four. An extra bit of information added to the 6 bit word M, is required to define the different angle region. As the counter counts only to four, the significance of the count has to be doubled. This is achieved by the insertion of a 2/1 multiplexer 35 (shown dotted) before the l of 8 decoder. The control of the multiplexer uses the extra bit of information and is switched for the duration of a bright-up pulse. The output of the multiplexer counts at twice the rate of the counter and hence the same peak value of the bright-up pulse is reached. The technique is used for angles of 74 58 to 77 and 58 to 77. 1
  • the delay circuit 14 and the pulse shping circuit 15 are in series, but that a switching circuit 60 allows the pulse shaping circuit to be by-passed.
  • the pulse shaping technique is only suitable for values of 0 in the ranges 58 to 90 and -5 8 to 90.
  • a further bit of information on Xst or Xop operates the switching circuit to bypass the pulse shaping circuit.
  • a final defect in the appearance of the line which must be overcome is flicker at the beginning and end of the line.
  • cyclic digital counter means operating in synchronism with the raster line scan so that successive counts of the counter correspond to successive sections of each raster line, thereby notionally dividing each raster line into sections respectively corresponding to different counts of the counter;
  • an output circuit comprising means for comparing said digital output with the output of the counter means to produce an output signal for changing said visual parameter when there is correspondence between said digital outputs and the output of the counter means;
  • delay means connectable to delay the output of said output circuit by a fraction of the period between successive counts of the counter means when a said digital output fractionally exceeds the corresponding count of the digital counter by a predetermined amount, thereby to effectively increase the number of sections into which each raster line is notionally divided.
  • the output circuit comprises means for comparing the digital outputs defining the beginning and end of the selected raster portion with the output of the cyclic counter and for developing an output signal during the period when the output from the counter is greater than or equal to the digital output defining the beginning and less than or equal to the digital output defining the end, of the selected raster portion.
  • said delay means includes a number of equal length delay circuits arranged to produce delays of 0, x, 2x nx (where n is the number of delay circuits, x is the delay of each delay circuit and (n 1) x equals the period between successive counts of the counting means); and an (n 1 multiplexer for selecting an appropriate delay according to the amount by which a said digital output exceeds the output of the digital counter.
  • said digital outputs define the beginning and end of each said raster line portion required to be selected, and said output circuit comprises means for producing an output signal when the digital counter output is greater than or equal to the digital output defining the beginning, and less than or equal to the digital output defining the end of a said raster line portion.
  • said delay means comprises means for delaying the beginning and end of the output signal of the output circuit by different amounts.
  • Display apparatus including pulse shaping means for shaping the output of the output circuit so that the degree of change in the visual parameter varies along the length of a said raster line portron.
  • the shaping means comprises circuitry for producing a signal having stepped leading and trailing edges.
  • Display apparatus including means for varying the number of steps forming the leading and trailing edges of the signal in dependence on the angle the desired symbol makes with the raster

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • Theoretical Computer Science (AREA)
  • Controls And Circuits For Display Device (AREA)
  • Video Image Reproduction Devices For Color Tv Systems (AREA)
US338842A 1972-03-10 1973-03-07 Display apparatus Expired - Lifetime US3894292A (en)

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GB1127572A GB1401022A (en) 1972-03-10 1972-03-10 Display apparatus

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US (1) US3894292A (de)
DE (1) DE2311826A1 (de)
FR (1) FR2175851B1 (de)
GB (1) GB1401022A (de)
IL (1) IL41679A0 (de)
IT (1) IT980539B (de)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4127850A (en) * 1974-10-03 1978-11-28 Smiths Industries Limited Scanning display apparatus
US4145754A (en) * 1976-06-11 1979-03-20 James Utzerath Line segment video display apparatus
US4231032A (en) * 1977-09-09 1980-10-28 Hitachi, Ltd. Variable accuracy trend graph display apparatus
US4276563A (en) * 1976-12-04 1981-06-30 Robert Bosch Gmbh Representing a video signal upon the picture screen of a video display device
US4298867A (en) * 1979-07-06 1981-11-03 System Concepts, Inc. Cathode ray tube character smoother
US4307393A (en) * 1977-11-11 1981-12-22 Hitachi, Ltd. Trend graph display system
US4318097A (en) * 1978-03-15 1982-03-02 Nippon Electric Co., Ltd. Display apparatus for displaying a pattern having a slant portion
US4454507A (en) * 1982-01-04 1984-06-12 General Electric Company Real-time cursor generator
US4496976A (en) * 1982-12-27 1985-01-29 Rockwell International Corporation Reduced memory graphics-to-raster scan converter
US4774508A (en) * 1985-08-15 1988-09-27 Citizen Watch Co., Ltd. Method of forming matrix image
US5028914A (en) * 1988-06-23 1991-07-02 Motorola, Inc. Method and apparatus for waveform digitization

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE2940088C2 (de) * 1979-10-03 1986-04-10 Hewlett-Packard Co., Palo Alto, Calif. Raster-Anzeigevorrichtung
US4622545A (en) * 1982-09-30 1986-11-11 Apple Computer, Inc. Method and apparatus for image compression and manipulation
JPS60191293A (ja) * 1984-03-12 1985-09-28 ダイキン工業株式会社 Ｃｒｔデイスプレイ装置の高速直線補間回路
GB2215570A (en) * 1988-03-01 1989-09-20 Kontron Instr Limited Improving the legibility of traces close to the line direction

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3388391A (en) * 1965-04-07 1968-06-11 Rca Corp Digital storage and generation of video signals
US3668687A (en) * 1969-11-17 1972-06-06 Sanders Associates Inc Raster scan symbol generator
US3671957A (en) * 1969-03-12 1972-06-20 Computer Optics Character generation display system
US3686662A (en) * 1970-11-12 1972-08-22 Int Standard Electric Corp Circuit arrangement for the presentation of waveforms on viewing screens utilizing raster deflection
US3792464A (en) * 1973-01-10 1974-02-12 Hitachi Ltd Graphic display device

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3388391A (en) * 1965-04-07 1968-06-11 Rca Corp Digital storage and generation of video signals
US3671957A (en) * 1969-03-12 1972-06-20 Computer Optics Character generation display system
US3668687A (en) * 1969-11-17 1972-06-06 Sanders Associates Inc Raster scan symbol generator
US3686662A (en) * 1970-11-12 1972-08-22 Int Standard Electric Corp Circuit arrangement for the presentation of waveforms on viewing screens utilizing raster deflection
US3792464A (en) * 1973-01-10 1974-02-12 Hitachi Ltd Graphic display device

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4127850A (en) * 1974-10-03 1978-11-28 Smiths Industries Limited Scanning display apparatus
US4145754A (en) * 1976-06-11 1979-03-20 James Utzerath Line segment video display apparatus
US4276563A (en) * 1976-12-04 1981-06-30 Robert Bosch Gmbh Representing a video signal upon the picture screen of a video display device
US4231032A (en) * 1977-09-09 1980-10-28 Hitachi, Ltd. Variable accuracy trend graph display apparatus
US4307393A (en) * 1977-11-11 1981-12-22 Hitachi, Ltd. Trend graph display system
US4318097A (en) * 1978-03-15 1982-03-02 Nippon Electric Co., Ltd. Display apparatus for displaying a pattern having a slant portion
US4298867A (en) * 1979-07-06 1981-11-03 System Concepts, Inc. Cathode ray tube character smoother
US4454507A (en) * 1982-01-04 1984-06-12 General Electric Company Real-time cursor generator
US4496976A (en) * 1982-12-27 1985-01-29 Rockwell International Corporation Reduced memory graphics-to-raster scan converter
US4774508A (en) * 1985-08-15 1988-09-27 Citizen Watch Co., Ltd. Method of forming matrix image
US5028914A (en) * 1988-06-23 1991-07-02 Motorola, Inc. Method and apparatus for waveform digitization

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Publication number Publication date
GB1401022A (en) 1975-07-16
FR2175851A1 (de) 1973-10-26
FR2175851B1 (de) 1979-05-11
DE2311826A1 (de) 1973-09-13
IT980539B (it) 1974-10-10
IL41679A0 (en) 1973-07-30

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