Display apparatus

• US 3,894,292 A
• Filed: 03/07/1973
• Issued: 07/08/1975
• Est. Priority Date: 03/10/1972
• Status: Expired due to Term

• Current Assignee: Brian Wilkinson, David John Jibb, Martin Neil Smith
• Original Assignee: Brian Wilkinson, David John Jibb, Martin Neil Smith
• Inventors: Wilkinson, Brian, Jibb, David John, Smith, Martin Neil
• Primary Examiner(s): Trafton, David L.
• Application Number:
  US05/338,842
• Time in Patent Office: 853 Days
• Field of Search: 340/324AD 315/22
• US Class Current: 345/441
• CPC Class Codes: G01R 13/22 Circuits therefor
• CPC Class Codes: G09G 5/20 Function-generator circuits, e.g. circle generators line or curve smoothing circuits

Abstract

Display apparatus in which line symbols are displayed by scanning a CRT in a raster and brightening up portions of the raster lines. The portion of raster line to be brightened-up is defined by a digital output. A cyclic counter produces a large number of pulses during each raster line to notionally divide each line into a number of equql length, sequentially numbered sections changes in the brightness being effected when there is correspondence between the digital output and the counter output.

Claims

1. Display apparatus in which the display comprises a raster of parallel lines and a symbol is displayed by changing a visual parameter of one or more selected portions of the raster lines comprising:

a. 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;

b. means for producing digital outputs defining the position of each raster line portion required to be selected to display a required symbol, in accordance with the notional numbering of sections of the raster lines effected by the counter means;

c. 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; and

d. 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.

2. Display apparatus according to claim 1, in which 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.

3. Display apparatus according to claim 1 wherein 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.

4. Display apparatus according to claim 3 wherein 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.

5. Display apparatus according to claim 4 wherein said delay means comprises means for delaying the beginning and end of the output signal of the output circuit by different amounts.

6. Display apparatus according to claim 1 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 portion.

7. Display apparatus according to claim 6, in which the shaping means comprises circuitry for producing a signal having stepped leading and trailing edges.

8. Display apparatus according to claim 7, 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 lines.