US3594756A

US3594756A - Crt curved character generator

Info

Publication number: US3594756A
Application number: US693671A
Authority: US
Inventors: Mauritz L Granberg; Howard N Hanson; Charles A Kiesling; Jerome J Stoffel
Original assignee: Sperry Rand Corp
Current assignee: Sperry Corp
Priority date: 1967-12-26
Filing date: 1967-12-26
Publication date: 1971-07-20
Anticipated expiration: 1988-07-20
Also published as: DE1816989B2; DE1816989A1; FR1596376A; GB1211948A

Abstract

A character generator for a cathode-ray tube display system including the capability of digitally generating curved characters. Each diode matrix used for generating a character produces output signals in digital form representing the Xcoordinate, the Y-coordinate, the intensity of the particular stroke of the character being drawn, the degree of departure of the stroke from a straight line if it is to be curved and the direction in which it is to be curved.

Description

United States Patent CRT CURVED CHARACTER GENERATOR 1 Claim, 15 Drawing Figs.

U.S. Cl 340/324,

235/l50.53 Int. Cl 606i 3/14 Field of Search IMO/324.1;

{56] References Cited UNITED STATES PATENTS 3,335,4l6 8/1967 Hughes 4. IMO/324.1

Primary Examiner-John W. Caldwell Assistant Examiner-Marshall M. Curtis Attorneys-Thomas J. Nikolai, Kenneth T. Grace and John P.

Dority ABSTRACT: A character generator for a cathode-ray tube display system including the capability of digitally generating curved characters. Each diode matrix used for generating a character produces output signals in digital form representing the X-coordinate, the Y-coordinate, the intensity of the particular stroke of the character being drawn, the degree of departure of the stroke from a straight line if it is to be curved and the direction in which it is to be curved.

TO DEF CIRCUIT PATENTEU JUL20 |97| LEFT Hub

RIGHT CRT CURVED CHARACTER GENERATOR BACKGROUND OF THE INVENTION In commonly assigned copending application Ser. No. 436,174 filed Mar. 1, 1965 (now U.S. Pat. No. 3,466,645) there is disclosed a digital data cathode-ray tube display system which generates alphanumeric characters by successively assembling a series of straight line segments in proper sequence until the character is completed. Each alphanumeric character is generated from an individual diode matrix which produces digital signals representative of X-coordinatcs, Y- coordinates and the intensity level of the individual line segment being drawn. These digital signals are then converted to analog signals which control the generation of the character and its intensity.

The characters generated are, therefore, of the straight line segment type and, while they are legible and easy to read, they do not have the natural appearance of the normal character. Further, because they do not have the natural appearance of normal characters, the viewing of such characters may become difficult over long periods of time.

SUMMARY The present invention provides an improved character generator which includes the capability of generating curved characters for the CRT display systems. Each diode matrix, in addition to producing digital signals representing the X-coordinate, Y-coordinate and intensity of a particular line segment also produces two digital output signals representing the degree of departure of the segment from a straight line of the line segment if a curved character is desired as well as two digital output signals representing the direction in which the segment is to be curved. Thus, for purposes of illustration, only, a diode matrix may produce three digital outputs representing the X-coordinates, three digital output signals representing the Y-coordinates, two digital output signals representing the intensity of the segment, two digital output signals representing the extent to which the segment is to be displaced orthogonally from a straight line if a curved character is desired and two digital output signals representing the direction in which the displacement is to take place.

As explained in the above identified copending application, a maximum of eight line segments are required to "paint" any desired alphanumeric character. Whenever digital signals are produced by a diode matrix which indicate that a particular line segment should be curved, a nine-phase clock enables a diode submatrix to produce digital signals which cause the line segment to be distorted or displaced from a straight line trajectory. The digital signals from the diode matrix also cause circuitry to produce digital output signals representing the maximum degree of displacement desired.

Thus, it is an object of the invention to provide character generating means including the capability for generating curved characters in the CRT display system.

It is also an object of the present invention to provide digital signals representing the degree of curvature orthogonal displacement desired.

It is still another object of the present invention to provide digital signals representing the direction in which the line segment is to be curved.

BRIEF DESCRIPTION OF THE DRAWINGS These and other more detailed and specific objects will be disclosed in the course of the following specification, reference being bad to the accompanying drawings, in which:

FIG. I is a generalized block diagram showing how the present invention relates to a display system as a whole;

FIG. 2a illustrates the prior art character generating matrix;

FIG. 2b illustrates a character traced with the matrix of FIG. 20;

FIG. 3a illustrates the diode coding circuitry used as the present character generating matrix;

FIG. 3b illustrates a character traced with the matrix circuit of FIG. 3a;

FIG. 3c is a chart showing the position of the beam for each stroke of the character;

FIG. 4 shows how FIG. 4a and FIG. 4b are related;

FIGS. 4a and 4b disclose the circuit details of the curvature circuit;

FIG. 5 illustrates the types of curves that can be produced with the circuit of the present invention;

FIG. 6 illustrates the 9 minor sequential scanning signals used to curve a particular stroke;

FIG. 7 is a table showing the amount ofdeflection caused by the minor sequential scanning signals;

FIG. 8 illustrates a push-pull deflection system incorporating the present invention;

FIG. 9 illustrates the generation of a curve in terms of deflection units; and

FIG. 10 illustrates the variety of curves obtained depending upon the length ofthe stroke to be curved.

DESCRIPTION OF THE PREFERRED EMBODIMENT The generalized block diagram shown in FIG. 1 illustrates how the present invention is related to the display system disclosed in the above identified copending application. Diode matrix 2 consists of an array of diode matrices arranged in rows and columns. Each of said matrices consists of a plurality of input lines, 8 for example, intersected at right angles by a plurality of output lines, 12, for example, when including the features of the present invention. Various ones of the input lines are coupled with diodes to particular ones of the output lines in accordance with the desired character that is to be generated.

Whenever coded signals from either the keyboard or the computer appear on line 4, character selection circuit 6 produces the proper signals on line 8 which select the desired character generation matrix from the array of matrices in diode matrix 2. No matter which of the matrices is selected, it produces digital signals representing an intensity control signal on line 10, digital signals representing the X-axis coordinates of one end of the line segment on line 12, digital signals representing the Y-axis coordinates of one end of the line segment on line I4 and digital signals on line 16 representing the magnitude or degree of curvature of a line segment that is to be curved as well as the direction in which it is to curve.

The clock 18 comprises a first source of sequential timing signals necessary for the operation of the system and is coupled into the diode matrix 2.

The digital intensity signals on the lines of cable 10 are coupled to D/A converter 20 which produces an analog output signal on line 22. This analog signal is coupled to the grid of cathode-ray tube 24 to control the intensity of the beam.

The X and Y-control signals on

cables

12 and 14 are coupled to a plurality of flip-

flops

26 and 28 respectively which store the signals and provide outputs to D/A converter 30. The analog signals produced by D/A converter 30 are coupled to driver 32 the output of which is coupled to the proper control elements of cathode-ray tube 24.

As stated earlier, each individual character matrix in the matrix array of of matrices produces digital output signals representing the extent of departure desired for a particular line segment from a straight line as well as digital output signals representing the direction in which the segment is to be displaced. These signals are present on cable 16 which is coupled to a plurality of flip-flops 36 which stores the signals. The output of the flip-flops 36 is coupled to encoder network 38 which produces analog signals on line 40 that are representative of the desired degree of curvature or displacement. These signals are coupled to driver 32 along with the X and Y-control signals.

The plurality of flip-flops 36 and encoder network 38, which receive clock signals on line 39, form the curvature circuit 34 of the present invention. The remainder of the circuit shown in FIG. I has been disclosed in the above identified copending application.

FIG. 2a and FIG. 2!) show the prior art character generating matrix for generating the character 8'' as disclosed in the above identified copending application. The matrix consists of eight input lines intersected at right angles (graphically) by eight output lines 44-58. When this particular matrix has been selected by the coded signals from the keyboard or the computer, the eight input lines 42 are sequentially energized and a signal appearing on each of these lines may pass through those diodes connected between that line and the output lines 4458. Thus, the diode coding circuit shown in FIG. 2a has the three purposes of representing in digital form the position of the cathode ray tube beam along the X-axis, the position of the beam along the Y-axis and the intensity of the beam as it sweeps between any two positions.

As shown in FIG. 2a the lower three

lines

54, 56 and 58 comprises a first group of output lines which indicate in binary form the X-coordinate of the CRT beam giving a possibility of eight increments or positions. As can be seen in the copending application mentioned previously only five of these eight possible positions are used. Also, lines 48, 50 and 52 comprises a second group of output lines which represent in binary form the Y-coordinate of the CRT beam and also give a possibility of eight different Y-coordinates. Again, as explained in the above identified copending application, only seven of these coordinates are used.

Also,

lines

44 and 46 represent the intensity of the beam during the interval of time the beam is sweeping from one position to the next as determined by the successi'. generation of signals along the eight input lines. Thus, if no diodes are present between the input lines and the

output lines

44 and 46, the beam is to be blanked and will not be seen on the face of the cathode-ray tube. If one diode connects line 46 to one of the input lines, one unit of intensity is indicated. If a diode connects line 44 with any one of the input lines, two units of intensity are indicated. If diodes connect both

lines

44 and 46 simultaneously to one of the input lines, three units ofintensi ty are indicated. As explained in the above identified copending application, by using the eight input lines, each character is generated by not more than eight strokes or movements of the cathode-ray tube beam. This is the reason that the eight input lines are sequentially scanned. During each scan, one stroke of the character to be generated is painted on the CRT screen. Since in forming a particular character some strokes are much shorter than others and since each stroke must be made in the same interval of time, some of the strokes would be brighter than others unless the intensity of the beam is controlled. With the circuit shown in FIG. 2a. ifa short stroke is to be made, only one diode will be connected between the input line and line 46. Ifa very long stroke is to be made, two diodes will be connected to the appropriate input line with one of them having the other end connected to output line 44 and the other of them having its other end connected to output line 46. If a medium stroke is to be made, the diode is connected from the appropriate input line to output line 44. Thus, it can be seen that for each stroke ofa particular character, a binary code represents the intensity of the beam during the generation of the stroke.

Consider now the generation of the letter B" from the circuit shown in FIG. 2a and as illustrated graphically in FIG. 2b. When the first scanning signal, 1 is applied to the input line indicated, the signal is passed through diodes to

output lines

44, 46, 48 and 50. Assuming the initial coordinates of the beam to be 0,0 it can be seen that the beam is now caused to move

coordinates

0,6. This is true since there is no output on the X lines 54, 56 and 58 and the outputs on

lines

48 and 50 are equivalent to 4 and 2 units respectively or 6 units along the Y-axis. Also, with both diodes coupled to

output lines

44 and 46, the intensity ofthe 6-unit stroke along the Y-axis is a maximum. When the next scanning signal 9 is applied to the input line indicated, the signal is passed through the diodes shown to

output lines

44, 48, 52 56 and 58. The signals on

lines

56 and 58 cause the beam to move 3 units along the X-axis. The signals on

lines

48 and 52 cause the beam to move to Y=5 along the Yaxis. Thus, the coordinates are now 3,5. The signal on output line 44 causes medium intensity of the beam. By continuing this procedure with the input scanning signals I the character B" can be traced out as shown in FIG. 2b.

FIG. 30, FIG. 3b and FIG. 36 show the character generating matrix used in the circuitry of the present invention. In order to compare the matrix with the prior art matrix discussed above, the diodes in FIG. 3a are connected to generate the character 8".

The matrix consists of eight input lines 62-76 intersected at right angles (graphically) by 12 output lines 78l00. Again, when this particular matrix, which is only one of an array of matrices, is selected by the coded signals from the keyboard or the computer, the eight input lines 62-76 are sequentially energized and a signal appearing on any one of these lines may pass through those diodes connected between that line and the output lines 78-100. Thus, the diode coding circuit shown in FIG. 3a produces digital outputs representing the position of the cathode-ray tube beam along the X-axis, the position of the beam along the Y-axis, the intensity of the beam as it sweeps between any two positions and the desired degree of curvature or orthogonal displacement of the stroke, if any, both in magnitude and direction Looking now at FIG. 30 it can be seen that the three

output lines

78, 80 and 82 comprises a first group of output lines which produce outputs in binary form representing the X- coordinate of the CRT beam and giving a possibility of eight increments or positions.

Also, lines 84, 86 and 88 comprises a second group of output lines which produce outputs representing in binary form the Y-coordinates of the CRT beam and also give a possibility of eight different Y-coordinates. Output lines 90 and 92 produce digital outputs representing the intensity of the beam during the interval of time the beam is sweeping from one position to the next as determined by the successive generation of signals along the eight input lines 62-76. Again, if no diodes are present between a respective input line and the output lines 90 and 92, the beam is to be blanked and will not be seen on the face of the cathode-ray tube. As explained with respect to the prior art character generating matrix, I, 2 or 3 units of intensity may be obtained by connecting the diodes between the input line and the proper output line or lines.

Output lines 94l00 comprises an additional group ofoutput lines which produce digital output signals representing the desired amount of curvature of a particular stroke with

lines

94 and 96 producing signals representing the magnitude of curvature desired and

lines

98 and 100 producing signals representing the direction of curvature. With respect to the CRT screen or face, the direction of curvature could be either UP and DOWN or RIGHT and LEFT or a combination of all of them. However, in the preferred embodiment as shown, the directions are designated RIGHT or LEFT. The signals on

lines

94 and 96 allow 3 of magnitude to be determined while a signal on line 98 causes a RIGHT curve and a signal on line 100 causes a LEFT curve,

Consider now the generation of the letter B from the circuit shown in FIG. 3a and as illustrated in FIG. 3b. FIG. 30 is a chart showing for each stroke the position of the beam as it moves from its present position X, Y to its new position X, Y' as well as the intensity of the beam and the curvature for that stroke including both magnitude and direction.

When the first scanning signal I is applied to input line 62, the signal is passed through diodes to

output lines

86, 88, 90 and 92. As can be seen in the chart in FIG. 30, the beam is caused to move only along the Y-axis for 6 units or increments. Since this is a long stroke, maximum intensity is required so both signals on lines 90 and 92 give a maximum intensity of3 units.

Stroke 2 is formed by applying the input signal to input line 64. The diodes cause output signals to be produced on

lines

80, 86 88 and 90. These signals cause the beam to remain at 6 units along the Y-axis but of move 2 units along the X-axis. Since this is a short stroke as can be seen in FIG. 3b, the signal on line 90 is used to cause minimum intensity ofl unit.

Stroke 3 is formed by applying scanning signal 3 to input line 66. The diodes are connected such as to cause output signals to be produced on

lines

80, 114, 66, 92, 94 and 96. The signal on line 80 causes the beam to remain at 2 units along the X-axis. However, the signals on

lines

84 and 86 cause the beam to move from 6 units to 3 units along the Y-axis. The stroke must be curved, however, and the signal on line 94 causes the stroke to have a first degree of curvature as expressed in arbitrary units. The signal on line 98 causes the stroke to curve to the RIGHT. As can be seen in FIG. 3b, with the magnitude of curvature involved the stroke is of medium length and therefore the signal on line 92 causes an intensity of 2 units as expressed in arbitrary units.

The other sequential input signals applied to the input lines 68-76 cause the remaining strokes of the character to be drawn as shown in FIG. 3b according to the values shown in the chart in FIG. 3c.

FIG. 4a and FIG. 4b, related as shown in FIG. 4, disclose the details ofcurvature circuit 34 shown in FIG. 1. Cable 16 is the same as that shown in FIG. 1 and contains the

conductors

94, 96, 98 and 100 from the diode matrix such as shown in FIG. 3a which are connected to the storage flip-flops 36 shown.

Conductors 98 and 11110 are connected to the SET and CLEAR sides respectively of flip-flop 102 which produces signals on lines 104 and 11116 that indicate whether the stroke is to be curved to the RIGHT or LEFT respectively. These signals are used in a manner to be explained hereinafter.

The signals on

lines

94 and 96 represent the desired amount of displacement or curvature of a particular stroke from a straight line and are stored in flip-

flops

108 and 110 respectively These flip-flops are of the well-known self-clearing type and, therefore, have only the SET input shown schematically. The output of flip-flops 108 and 1110 are coupled first to AND gates 112, 114 and 1116 which produce signals for determining the magnitude of curvature desired and, secondly, are coupled to OR gate 118 which initiates signals for generating the curve.

If neither of the

conductors

94 or 96 have signals present thereon, both flip-

flops

108 and 110 are CLEARED and neither the AND gates 1112, 114, 116 nor OR gate 118 can produce output signals. If, however, a signal is present on conductor 94, flip-flop 1118 will be SET and will produce an output signal on line 120 which is coupled to AND gate 112 as a first input signal. Since flip-flop 110 is CLEAR at this time, it will produce an output signal on line 122 which is coupled to AND gate 112 as a second input. AND gate 112 then produces an output on line 124 which represents a curve of the first degree as shown in FIG. 5.

If there is a signal present on conductor 96 but none on conductor 94, flip-flop 110 will be SET but flip-flop 108 will be CLEAR. Flip-flop 110 will produce an output on line 126 under these conditions while flipJlop 108 will produce an output on line 128. Lines 126 and 128 are coupled to AND gate 114 which will produce an output on line 130 which represents a second degree curve as shown in FIG. 5.

If there are signals present on both

lines

94 and 96, both of the flip-flops 108 and 1111 will be SET and will produce signals on lines 120 and 1126 respectively both of which are coupled to AND gate 116 which then produces an output signal on line 132 which represents a third degree curve as shown in FIG. 5. These signals on

lines

124, 130 132 which represent first, second and third degree curves will be used in a manner to be explained hereinafter.

In any case, if either of the flip-flops 1611 or 110 is SET signals will be produced on either or both

oflines

120 and 126 both of which are connected to OR gate 118. Thus, OR gate 118 will always provide an output signal on line 1134 whenever either ofthe flip-

flops

108 or 110 is SET.

It will be remembered from the earlier discussion of the character generating diode matrix that eight sequential scanning signals, through 1 are used to generate a character. Thus, each phase represents one stroke of the character up to a maximum of eight strokes per character. In order to curve a particular stroke, the present invention utilizes a second source of sequential signals which produce 9 minor sequential scanning signals or phases, 1 through 4 as shown in FIG. 6. Thus, if, during 1 it is desired to curve the first stroke, the 9 minor phases, 1 through 1 are generated. In like manner, any of the remaining possible seven strokes may be curved.

Returning now to FIG. 4a, it will be seen that the output of OR gate 118 on line 134 is coupled as one input to each of the AND gates 136-151). The other input to each of the AND gate 136-150 is a respective one of the minor scanning signals Pf- 1 The ninth minor scanning signal, 1%,, is not used for gating purposes but is used to create a necessary delay as will be pointed out during the discussion of the third degree curve shown in FIG. 5. The outputs of the AND gates 136-1511 are used to strobe or sequentially scan an encoding means which in the preferred embodiment is a diode matrix.

Thus, whenever a stroke is to be curved and OR gate 118 is producing an output signal that is coupled to AND gate 136 along with the minor scanning signal 1 AND gate 136 produces an output on line 152 that is coupled through

diodes

154, 156 and 158 to output lines A, C and D of the diode matrix encoder. Likewise, the output of AND gate 138 on line 160 will be coupled through appropriate diodes as shown to output lines A, B and D. In a similar manner, the output of AND gate 146 on line 162 will be coupled through appropriate diodes to output lines A, B, C and D. Also, the output of AND gate 142 on line 164 will be coupled to the diodes shown to output lines A, B, C, D and E. The outputs of AND

gates

144, 1146, 148 and 150 are coupled to the output lines A, B, C, D and E in the manner described above in relation to AND gates 136, I36, and 142 but in the reverse order. Thus, the outputs of AND gates 136 and are connected to the same output lines while the outputs of AND

gates

138 and 1148, 1140 and 146, and 142 and 144 are coupled to the same output lines respectively.

The outputs of the diode matrix on lines A, B, C, D and E are coupled to 15 AND gates 166-194 in FIG. 4b. The output on line A is coupled to AND gates 166-170, line B to AND gates 172-176, line C to AND gates 178-182, line D to AND gates 184-188 and line E to AND gates 1190-194. Thus, there are five groups of three AND gates per group.

To each AND gate in each group there is coupled one of the three

lines

124, 130 and 132 which carry the signals representing the 3 of curvature that are available.

Thus, each of the AND gates 166-194 have as one input a signal fromone of the lines A, B, C, D or E which represent that a curve is to be produced and as a second input one of the signals on

lines

124, 130 and 132 representing the degree of curvature to be obtained. The outputs of AND gates 166- 1194 are then used to obtain the desired degree of curvature.

All of the AND gates 168-194 produce outputs which are coupled to OR gates 196-2116 to cause certain ones of them to produce outputs. The left most AND gate 166 produces an output which is coupled to AND gate 206 while the other six AND gates 210-226 receive one input from each of the OR gates 1196-266 respectively. The other input to the AND gates 268-220 is from the conductor 1114 which, when a signal is present thereon, represents that the stroke is to be curved to the RIGHT.

Each of the AND gates 2118-220 produces an output which is coupled to a respective one of amplifiers 222-234. The output of each amplifier is connected in common to the deflection coil via a resistor, conductor 234 and driver 236. Also coupled to driver 236 via conductor 236 is the deflection control circuitry as described in the above identified commonly assigned copending application.

The numbers appearing beside the resistors connected to amplifiers 222-234 shown in FIG. 4(b) represent the various weights" of the respective resistors and correspond to deflection values. Thus, a stroke with a curve of the first degree will be drawn when the amplifiers connected to resistors having weighted values of 2, I, one-half, one-fourth and one-eighth are activated. Likewise, a stroke with a curve of the second degree will be drawn when the amplifiers connected to resistors having weighted values of 4, 2, l, one-half, one-fourth and one-eighth are activated. Finally, a stroke with a curve of the third degree will be drawn when the amplifiers connected to resistors having weighted values of 8, 4, 2, l, one-halt, onefourth and one-eighth are activated.

In order to better understand the operation of the above described circuit, consider the example wherein a stroke with a curve of the third degree is to be drawn. First, a code corresponding to a curve of the third degree is set up in the character generating matrix. Thus, in FIG. 3(a) if the stroke which is to have a curve of the third degree is that stroke which will be formed when (I), ofthe sequential scanning voltages is applied to input line 62, a first diode will have to be connected from input line 62 to output line 94 and a second diode will have to be connected from input line 62 to output line 96. Thus, output signals appear on both

output lines

94 and 96. Assume also that the stroke is to be curved to the right. In that case a diode would also be connected between input line 62 and output line 98. An output signal would ap pear on line 98 indicating that the stroke is to curve to the RIGHT. This signal is coupled to the flip-flop 102 in FIG. 4(a) which SETS it and causes a signal to be produced on line 104. Also the output signals from the character generating matrix in FIG. 3(a) on

lines

94 and 96 are coupled to flip-

flops

108 and 110 respectively which produce outputs on

lines

120 and 126 respectively. These signals activate AND gate 116 and cause an output to be produced on line 132 which indicates that a curve of the third degree is to be drawn. The signals on

lines

120 and 126 are also coupled to OR gate 118 which produces an output on line 134 which provides a first enabling signal to AND gates l36-l50. Thus, when strobe pulses b, I are sequentially applied to AND gates 136-450, signals are produced on output lines A, B, C, D and E according to the manner in which the diodes are connected. When minor strobe pulse 9, is applied to AND gate 136, an output is produced on line 152 which is connected through diodes to output lines A, C and D.

Looking now at FIG. 4(b), it can be seen that the output on line A is connected as one enabling pulse to AND

gates

166, 168 and 170. In like manner, the output on line C is coupled as one enabling pulse to AND

gates

178, 180 and 182. Also, the output on line D is coupled as one enabling pulse to AND

gates

184, 186 and 188. It will also be seen that the signal on line 132 which represents a third degree curve is coupled as a second enabling pulse to AND

gates

166, 178 and 184. It is also coupled as an input to AND

gates

172 and 190 but since these gates do not have a first enabling input pulse they cannot produce an output. However, AND

GATES

166, 178 and 184 will all produce an output since both inputs are enabled.

The output of AND gate 166 is connected directly as one input to AND gate 208. The output of AND gate 178 is connected to OR gate 198 which produces an output that is connected as one input to AND gate 212. Also, the output of AND gate 184 is coupled to OR gate 200 which produces an output that is coupled as one input to AND gate 214. The other input to each of the AND

gates

208, 212 and 214 is the signal on line 104 which represents that the stroke is to be curved to the right. AND

gates

208, 212 and 214 each produce a signal that is coupled to

amplifiers

222, 226 and 228 respectively, resistors having weighted values of 8, 2 and 1 respectively, and to common line 234 which is connected to the driver amplifier 236. It will be noted that the total value of the resistors is the sum of 8, 4, 2, l, one-half, one'fourth and one-eighth "/s or approximately l6, Thus, in the above example, the beam will be deflected eleven-sixteenths of the total amount during 1 scanning pulse when a curve of the third degree is required. See FIG. 7. This point is shown as point 240 on the third degree curve illustrated in FIG. 5. In like manner, during the application of the minor scanning pulse 1 outputs are produced on lines A, B and D which cause the necessary circuits to select

weighted resistors

8, 4 and 1 which will cause the electron beam to be deflected thirteen-sixteenths of the total amount. This point is shown as point 242 in FIG. 5. As can be seen from the Table in FIG. 7, each of the other minor scanning pulses causes the beam to be deflected a particular amount depending upon the combination ofdiodes in the diode matrix shown in FIG. 30.

FIG. 5 shows each of the 3 of curvature or orthogonal displacement from a straight line path which can be obtained through the selection ofthe proper weighted resistors.

In order to draw a curve to the LEFT, reference is made to FIG. 8 which illustrates the push-pull arrangement described in the above identified commonly assigned copending application and incorporating the curve generator of the present invention. Amplifier 244 represents the group of amplifiers 222-234 and associated weighted resistors shown in FIG. 4b as well as any needed driver circuits. Amplifier 246 represents a similar group of amplifiers, driver circuits and weighted resistors necessary for moving the electron beam to the LEFT. As shown in FIG. 4b, AND gate 208', shown in dotted outline, represents one of the AND gates for the curve LEFI' circuit. The signal on dotted line 106, representing a curve LEI'T, is shown coupled to AND gate 208 in dotted outline. This is to indicate that the seven AND gates 208-220, seven amplifiers 222-234 and associated resistors are duplicated for the curve LEFT circuit. Separate logic is required but since it is exactly the same as that illustrated for the curve RIGHT circuit shown, it is not shown here in detail. Dotted lines are shown where the separated logic would continue on. Below that level, all logic used is common.

Consider now FIG. 9 which shows the generation of a curve in terms of deflection units. Assume that the electron beam is to move from the origin 0 to the end point E along the Y-axis. The nine minor strobe pulses are represented along the Yaxis. As the beam begins to move from the origin 0, the curve generating circuits cause the beam to begin to be distorted to the right. This is shown as 3 arbitrary units in FIG. 9 and the beam is at point 248. The resultant path 250 is obtained. As minor strobe pulse 9 is applied to the curve generating circuits, the beam is continuing to move along the Y-axis and is distorted even further along the X-axis to point 252 with the resultant path 254 obtained. This process continues until minor strobe pulse 1 is produced which causes the beam to move to point 256 thereby obtaining the resultant path 258. Since there is no minor strobe pulse 4%, the beam returns to the Y-axis along path 260.

FIG. 10 shows the variety of curves that are obtained depending upon the length of the stroke that is to be curved.

Thus an improved character generator has been disclosed which includes a curved line segment generator which produces digital signals representing both the degree and direction of curvature ofa particular stroke.

We claim:

1. In a CRT display system having driving circuits coupled to deflection coils for generating alphanumeric characters composed of individual line segments, a circuit for curving selected ones of said line segments comprising:

a. a character generator for generating n sequential groups of digital signals necessary to produce an alphanumeric character formed of n variable length line segments, each of said n groups of digital signals including first signals representing one of said line segments and second signals representing the degree of displacement from a straight line path for each line segment,

b. a curve generator coupled to said character generator for receiving said second signals and generatingj sequential groups of digital signals during the time each of said n groups of digital signals is being generated, each of said] groups of dlgltal signals representing the extent of orthogonal displacement from a straight line path of one of said n line segments at a corresponding one of j locatrons along said segment.

- a first and second plurality of l) A converters having their outputs connected to said driving circuits, said first plurality of converters having their inputs coupled to said character generator for receiving said first signals in each of said It sequential groups of signals and producing analog signals for sequentially generating the n segments of said alphanumeric character.

gate means coupling said j sequential groups of signals to said second group of D/A converters for producing a current through said deflection coils, and

. a translator coupled to said character generator for

Claims

1. In a CRT display system having driving circuits coupled to deflection coils for generating alphanumeric characters composed of individual line segments, a circuit for curving selected ones of said line segments comprising: a. a character generator for generating n sequential groups of digital signals necessary to produce an alphanumeric character formed of n variable length line segments, each of said n groups of digital signals including first signals representing one of said line segments and second signals representing the degree of displacement from a straight line path for each line segment, b. a curve generator coupled to said character generator for receiving said second signals and generating j sequential groups of digital signals during the time each of said n groups of digital signals is being generated, each of said j groups of digital signals representing the extent of orthogonal displacement from a straight line path of one of said n line segments at a corresponding one of j locations along said segment, c. a first and second plurality of D/A converters having their outputs connected to said driving circuits, said first plurality of converters having their inputs coupled to said character generator for receiving said first signals in each of said n sequential groups of signals and producing analog signals for sequentially generating the n segments of said alphanumeric character, d. gate means coupling said j sequential groups of signals to said second group of D/A converters for producing a current through said deflection coils, and e. a translator coupled to said character generator for receiving said second signals and producing outputs which are coupled to said gate means, said translator generating any one of r signals each of which represents a different extent of displacement said r signals enabling selected ones of said gate means whenever any one of said n line segments is to be curved such that the j sequential groups of signals are coupled to selected ones of the D/A converters in said second group whereby said selected one of said n line segments is orthogonally displaced the desired degree at j points along said segment.