Vector generator

• US 4,027,148 A
• Filed: 09/10/1975
• Issued: 05/31/1977
• Est. Priority Date: 09/10/1975
• Status: Expired due to Term

• Current Assignee: Cinematronics Incorporated
• Original Assignee: Lawrence David Rosenthal
• Inventors: Rosenthal, Lawrence David
• Primary Examiner(s): Smith, Jerry
• Application Number:
  US05/612,045
• Time in Patent Office: 629 Days
• Field of Search: 235/151, 235/198, 315/367, 315/379, 315/383, 315/386, 340/324 A
• US Class Current: 708/274
• CPC Class Codes: G09G 1/08 the beam directly tracing characters, the information to be displayed controlling the deflection and the intensity as a function of time in two spatial co-ordinates, e.g. according to a cartesian co-ordinate system

Abstract

A vector generator having a digital input and a cathode ray tube (CRT) display output is disclosed. Digital values specifying the initial point of the line segment in Cartesian coordinates are converted to proportional voltages applied across the capacitors of two identical resistance-capacitance networks which control the positioning of the CRT beam. A second pair of digital values defining the length and direction of the line segment with respect to the initial point are normalized digitally by left shifts until the larger of the pair equals or exceeds a normalization constant. The normalized values are added to the initial point coordinates, and the sums are then converted to proportional voltages applied to the resistors of the two networks. Simultaneously, a timer preset during the normalization operation is started and the CRT beam is turned on to start the drawing of the line segment. As a result of the normalization, the voltages applied to the RC networks are larger than needed to draw the segment. Consequently, the beam will be turned off by the timer well before the outputs of the RC networks reach the applied voltages. Thus, line segments of widely differing lengths are drawn at a normalized fast rate and are displayed at a normalized uniform visual intensity on the CRT.

Claims

1. Method for drawing line segments having normalized visual intensity on a cathode ray tube display screen from digital information including for each segment the steps of:

a. receiving a first set of digital values of planar coordinates of a starting point of a line segment to be drawn from a source of digital information;

b. converting said digital starting point values into deflection voltages directly related to the magnitudes of said values;

c. charging a pair of matched passive networks having the same predetermined time constant which remains unchanged regardless of line segment length to the respective levels of said deflection voltages;

d. positioning a drawing beam of said display at said starting point by said deflection voltages stored in said networks;

e. normalizing a second set of digital values defining said line segment relative to the starting point thereof by repeatedly multiplying said second set of digital values by the same factor until the larger of the two final products resulting therefrom equals or exceeds a predetermined normalization constant;

f. digitally adding each of said two final products to the corresponding one of said starting point coordinate values respectively to produce digital sums;

g. converting said digital sums into drawing voltages directly related to the magnitudes of said sums;

h. turning on said beam to start drawing, and simultaneously applying said drawing voltages to said charged networks to deflect said beam along the display locus of said segment to be drawn;

i. reducing the drawing time required to complete said segment by an amount related to the number of multiplication repetitions utilized in normalizing said digital values defining said line segment relative to the starting point;

j. turning off said drawing beam when a terminal end of said segment has been reached.

2. The method as set forth in claim 1 wherein normalization of said digital values defining said line segment relative to the starting point thereof is accomplished by repeatedly multiplying said second set of digital values by the factor of two until the larger of the products resulting therefrom equals or exceeds a predetermined normalization constant.

3. The method as set forth in claim 1 wherein said drawing beam is turned off when said charging networks have charged to voltage levels which are less than half the applied drawing voltages.

4. The method as set forth in claim 3 wherein said voltage levels corresponding to the position of said drawing beam being at the terminal end of said line segment are determined by the termination of a time duration determined during said normalization step.

5. The method as set forth in claim 1 wherein the drawing rates of said line segments are normalized within a factor of 2√

2.

6. Improved electronic apparatus for drawing a line segment having normalized visual intensity without regard to line segment length on a screen of a cathode ray tube display without variation of beam current, from coordinate information supplied by a digital computer connected to said apparatus, said computer including a system sequencing means for sequencing between operations, said improved apparatus including in combination:

a. digital register means for holding coordinate values of a starting point of a said line segment to be drawn;

b. digital shift register means for holding values defining the length and direction of said line segment relative to said starting point and for multiplying said length and direction values by a factor in said digital register means until the larger of the two resultant final products equals or exceeds a predetermined normalization constant;

c. digital adder means for adding said final products to said starting point values to produce sums and for transferring said sums into said digital register means;

d. digital to analog converter means connected to said digital register means for converting said starting point coordinate values into proportional voltages during a first time interval and for converting said sums into proportional voltages during a second time interval;

e. two passive networks having equal time constants that remain constant without regard to line segment length;

f. two beam deflection drivers, each being connected to one of said networks and to said display for deflecting a drawing beam thereof along a locus defining each said line segment in accordance with the instantaneous voltage levels of said networks;

g. first switch means connected between said digital to analog converter means and said networks for charging said networks to said starting point proportional voltages during said first interval;

h. system sequencer means in said digital computer and connected to a beam control element of said display and to said shift register means for turning on said beam when said sum voltages are applied to said networks and for turning off said beam;

i. line length timer means connected to said system sequencer means for signalling beam turn off after a time interval determined by said line length timer means in response to a function of the number of multiplications performed by said shift register means in generating said products.

7. The electronic apparatus of claim 6 wherein said digital shift register means comprises two shift registers, each said shift register having predetermined bit positions connected to provide inputs to one of two exclusive OR gates, the outputs of said exclusive OR gates providing the inputs to a two input OR gate, having an output which is connected to provide an input to said system sequencing means, whereby dissimilar bits in said predetermined bit positions of one or both of said shift registers indicate to said sequencing means the completion of normalization.

8. The electronic apparatus of claim 6 wherein said digital line length timer and control means includes a digital counter with an output signalling completion of said line segment upon reaching a predetermined count and preset inputs connected to a decoder generating preset values as a function of the number of multiplication repetitions performed in generating said products.