US3603967A

US3603967A - Character generator

Info

Publication number: US3603967A
Application number: US820118A
Authority: US
Inventors: Markvard Hauerbach
Original assignee: Stromberg Datagraphix Inc
Current assignee: ANACOMP Inc 11550 NORTH MERIDAN STREET CARMEL INDIANA 46032 A CORP OF INDIANA
Priority date: 1969-04-29
Filing date: 1969-04-29
Publication date: 1971-09-07
Anticipated expiration: 1988-09-07
Also published as: JPS4916206B1; FR2040362A1; DE2020522A1; GB1244949A

Abstract

A character generator is described for producing deflection of a beam in a cathode-ray tube to generate selected characters on its screen. Deflection information representing the selected character is generated by a set of wires (one set for each character) wound on a series of magnetic cores and is read out by sequential energization of the cores. The signals produced by the set are utilized to control charging circuits which produce constant current output signals of appropriate sign representing increments of beam deflection to generate the selected character. The output signals are accumulated by a pair of storage means which are respectively adapted for connection to the horizontal and vertical deflection means of the cathode-ray tube.

Description

United States Patent [72} Inventor Mlrkvard Hum-inch 3,325,802 6/1967 Bacon 340/324 San Dlego,CllK. 3,329,947 7/1967 Larrowe etal n 340/324 [2|] Appi NO, 320418 3,466,612 9/l969 Myers et al 340/324 X Fikd P" 291 Primary Examiner-John W. Caldwell [45] PalFmed Assistant ExaminerDavid L. Trafton [73] Ass'gnce slmmbtrl Dual-pm AlmmeyAnderson, Luedeka, Fitch, Even and Tabin San Diego, Calif.

[54] CHARACTER GENERATOR ABSTRACT: A character generator IS described for produc- 36 Claim, 25 D aw g "3 s mg deflection of a beam in a cathode-ray tube to generate [52] Us. CL 340/324 A, selected characters on i screen Deflection information 315/18 315/30 representing the selected character is generated by a set of [SI] llll. CL i G06! 3/14 wires (one set for each character) wsmnd on a series of [50] 340/3241, netic cores and is read out by sequential cncrgization f the 324 A cores. The signals produced by the set are utilized to control charging circuits which produce constant current output [56! R'lem CM signals of appropriate sign representing increments of beam UNITED STATES PATENTS deflection to generate the selected character. The output 2,920,3[2 ["960 Gordon et a1. 340/324 X signals are accumulated by a pair of storage means which are 2,931,022 3/1960 Triest 340/324 respectively adapted for connection to the horizontal and vet- 3,222,667 12/1965 Woroncow et 340/324 tical deflection means ofthe cathode-ray tube.

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INVENTOR MARKVARO I'IAUERBACH CHARACTER GENERATOR This invention relates to character generators for use with cathoderay tubes having deflection plates or deflection coils. More particularly, the invention relates to a character generator which generates deflection voltages for cursively writing characters. rather than deflection voltages representative of a raster scan or other type of fixed pattern scan.

Cathode-ray tubes are frequently utilized in connection with electronic computers for providing a display of information representative of the output of the computer. Synthesis of characters by providing appropriate deflection voltages to suitable deflection devices in a cathode-ray tube may be accomplished by several different techniques. One such technique involves causing the cathode-ray tube to be deflected through a raster scan or other type of fixed pattern scan which is the same for all characters. The cathode-ray tube beam is allowed to impinge upon the tube screen only at certain times during the scan, such as by appropriate variations of grid voltage, depending upon the particular character being generated. This character generation technique has the disadvantage that a fixed and relatively long period of time is required for each character, irrespective of the complexity or simplicity of the character being generated. Thus a considerable amount of time is wasted due to the necessity of completing the full scan for each character.

In order to more efficiently utilize time, techniques have been developed for character generation in which deflection voltages are produced for writing the characters cursively, rather than by utilizing a raster scan or other type of fixed pattern scan. Such techniques typically form the characters in a series of dots or strokes. suitable provision being made for blanking the electron beam at appropriate times, although most of the alphabetic and numeric characters can be generated without such blanking during the generation of the character. Character generators utilizing such cursive writing techniques include provision for storing a considerable amount of inforrnatioi'i. depending upon the complexity and number otchararrters to be generated.

M any character generators of the cursive writing type incor' porate a number of magnetic, resistive or diode devices inter' connected by a wiring pattern. Either the state of the devices or the configuration of the wiring pattern serves for storing the character shape information. Such generators also incorporate logic circuitry utilizing analytic techniques for producing the required deflection voltages from the information in the storage devices. Typically such character generators require a relatively large number of devices or a complex wiring pattern and as the number of characters or the complexity of the charucters increases, a corresponding increase in the complexity of the character generator results. Moreover, such types of character generators sometimes suffer from poor character registration, uneven intensities and discontinuities between various parts of characters, and are typically limited in the available character styles which may be produced. Furthermore, many known information storage and readout systems for character generators are subject to undesired interference from signals representative of unselected characters.

It is an object of this invention to provide an improved character generator for use with a cathode-ray tube.

Another orject oi" the in ention is to provide a character generator in whicn the required number of components per character is reduced over heretofore known devices of corresponding capability.

A further object of the invention is to provide a character generator which u ilizes a simple and low cost means ofinformation storage.

Still another object of the invention is to provide a character generator in which character selection is accomplished with minimal interference from unselecctl charac ers.

It is a further object of the invention to provide a character generator which utilizes cursive writing of characters rather than a raster scan or other type of fixed pattern scan. and which provides good character registration, even intensities and continuity between various parts of characters, and freedom in design of character styles.

Other objects of the invention will become apparent to those skilled in the art from the following detailed description, taken in connection with the accompanying drawings wherein:

FIG. 1 is a block diagram of a character generator constructed in accordance with the invention and illustrating, schematically, a cathode-ray tube used in connection therewith;

FIG. 2 is an illustration of the character G as formed by utilizing the character generator illustrated in FIG. I as a dottype generator;

FIG. 3 is a series of graphs illustrating the operation of the character generator of FIG. I in producing the character 6 as illustrated in FIG. 2;

FIG. 4 is an illustration of a dot sequence of tin: character V produced by the character generator of FIG. 1 utilized as a dot-type generator as it would appear on the cathode-ray tube screen (a) without the proportioning circuit, and (h) with the proportioning circuit;

FIG. 5 is a circuit diagram of part of the apparatus as FIG I in a configuration for dot-type character generation;

FIG. 6 is a circuit diagram illustrating a stage in one type of pulse generator which may be utilized in the character genera tor of FIG. 1;

FIG. 7 is a circuit diagram of an intensity circuit as used in the character generator of FIG. I for dottype character generation;

FIG. 8 is a circuit diagram of an enlarging circuit as may be used in the character generator of FIG. 1;

FIG. 9 is a circuit diagram of a diminishing circuit which may be used in the character generator of FIG. 1;

FIG. I0 is a circuit diagram ofa clamp circuit which may he used in the character generator of FIG. I;

FIG. 11 is a diagram illustrating the available strokes when the character generator of FIG. I is utilized as a strnlw ype character generator;

FIG. 12 is an illustration of the letter L as fo med by ut|liz ing the character generator of FIG. I as a stroke-type character generator;

FIG. I3 is a series of graphs illustrating the operation of the character generator of FIG. I as a stroke-ty e generator to produce the letter C as illustrated in FIG. I2;

FIG. 14 is a circuit diagram of a portion of an cttcmfilly timed sequential pulse generator which may used in the character generator of FIG. 1;

FIG. 15 is a circuit diagram of a portion ofa charging circuit which may be utilized in the character generator of FIG. I for producing characters by the stroke type generation illttsli'alrri in FIGS. 12 and 13;

FIG. 16 is a circuit diagram of an intensity circuit as may be utilized in the character generator of FIG. 1 for stroke-type character generation of characters as illustrated in FIGS 12 and 13;

FIG. 17 is a block diagram of another embodiment oi" the in vention;

FIG. I8 is a block diagram of a further embod ment of the invention;

FIG. 19 is a diagram illustrating the available s rokes in the embodiment of FIG. I8;

FIG. 20 is a circuit diagram of a charging current generator which may be utilized in the embodiment of FIG. 18.

FIG. 21 is a circuit diagram of a brightness compensating circuit which may be utilized in the embodiment o FIG. 18;

FIG. 22 is a block diagram of a code converter suitable for use in the character generator of FIG. IS;

FIG. 23 is a block diagram of a gated clock generator which may be employed to drive any of the cha acter generators described herein;

FIG. 24 is a circuit diagram of a buffer amplifier which may be used to drive electromagnetic deflection yokes if the latter are used in place of electrostatic deflection plates to produce deflection fields; and

PK}. 25 is a circuit diagram of a deflection yoke driver for use with the circuit of FIG. 24.

Very generally the character generator of the invention comprises a plurality of magnetic cores 11 and means 12 for sequentially energizing such cores. (See HO. 1.) A set of wires 13 is provided for producing information to generate a predetermined character. Respective wires in each set are wound on selected cores to produce. upon energization of the cores, pulses representative of incremental changes in beam deflection. Charging means 14 are provided for receiving the pulses produced in the wires upon energization of the cores. The charging means produce constant current output signals each of a predetermined duration corresponding to an increment of X' or Y-axis deflection. Storage means 16 and 17 are connected to the charging means to receive and accumulate the output signals supplied thereto from the charging means, thereby producing deflection voltages corresponding to the sum of the X- and Y-axis deflection increments. respectively. The storage means 16 and 17 are adapted for connection to the X-axis and Y-axis deflection means, 18 and 19, respectively, of a cathode-ray tube 21, to apply X-axis and Y-axis deflec tion voltages to the deflection plates.

GENERAL CONSTRUCTION AND OPERATION Referring now particularly to H0. 1, the general construc tion and operation of a character generator constructed in accordance with the invention will be described. Information for each character is generated in a respective one of a plurality of sets of wires 13. In the illustrated embodiment, there are three wires in each set, only one set being illustrated. One wire generates X-axis deflection voltage information in accordance with the manner in which it is wound or not wound on each of a series of magnetic cores 1]. When the cores are closed rings, threading the wire through selected cores is sufficient to generate deflection information. A second wire generates the Y-axis deflection voltage information in the same manner. A third wire is utilized for some characters for which it is necessary to generate information indicating when the electron beam of the cathode-ray tube 21 is to be blanked during part of the character generating period; e.g. to prevent tracing the same segment of the character twice. Pulses representative of incremental changes in beam deflection, and blanking or unblanking of the electron beam, are produced by sequentially energizing the cores ll. lf a wire is wound on a particular core, when the core is energized a pulse is produced in that wire, the polarity of the pulse depending upon the direction with which the wire is wound.

The sequential pulse generator 12 is utilized to energize the cores 11 sequentially. The circuitry for the sequential pulse generator may be of any suitable type, and specific types of circuits which may be utilized are shown in FIG. 6 and are described in detail subsequently. Generally, the sequential pulse generator may comprise a plurality of blocking oscillators, each connected to provide an output pulse for energizing one of the cores and for triggering the next succeeding blocking oscillator. Each magnetic core 11 may comprise the core of the blocking oscillator transformer, thus providing a substantial saving in the number of parts required. Where the timing of the pulse is particularly important, such as in the case of utilizing the illustrated apparatus as a stroke-type character generator, the sequential pulse generator may be timed with a suitable external clock oscillator, not illustrated in FIG. 1. The number of magnetic cores utilized determines the total number of available dots or stokes, and this may be varied to suit requirements. It has been found that a series of 18 to 20 cores provides a satisfactory number of dots or strokes, plus pulses indicative of starting and stopping each character as described below.

The particular set of wires for the production of the desired character which it represents is selected by character selection logic 22 which is coupled to one end of each set of wires. The character selection logic, the circuit of which is shown in FIG. 5 and is described fully below, receives information on the character to be selected from a computer, not shown. The end of each set of wires opposite the character selection logic is connected to

gates

23, 24 and 26 for the X-axis deflection, Y- axis deflection and beam intensity functions, respectively. The

gates

23, 24 and 26, as will be explained below, comprise OR gates which pass the outputs of a selected set of wires in response to appropriate operation of the character selection logic. The energizing pulses applied to each core by the sequential pulse generator 12 are so shaped as to result in the production of a single trigger pulse in each wire wound on that core for each core energization. The polarity of the trigger pulses depends upon the direction in which the wire is would on the core.

The outputs of the X-axis deflection gate 23 and the Y-axis deflection gate 24 are applied to the charging means 14. The charging means operate in response to such trigger pulses to produce constant current output signals representative of increments of horizontal and vertical deflection. In the embodiment illustrated in FIG. 1, the charging means 14 include an X-axis pulse detector 27, a Y-axis pulse detector 28, a positive X-axis charging circuit 29, a negative X-axis charging circuit 31, a positive Y-axis charging circuit 32, and a negative Y-axis charging circuit 33. The X-axis pulse detector 27 separates trigger pulses applied to it from the gate 23 (such pulses being produced in the uppermost of the wires 13 and being representative of increments of X-axis deflection) and applies the positive pulses to the positive X-axis charging circuit 29 and applies the negative pulses to the negative X-axis charging circuit 31. Similarly, the Y-axis pulse detector 28 applies positive pulses to the positive Y-axis charging circuit 32 and negative pulses to the negative Y-axis charging circuit 33, depend ing upon the polarity of trigger pulses applied to the pulse detector 28 from the gate 24, such pulses being produced in the middle one of the wires 13. A circuit which may be employed for the charging means is shown in FIG. 5 and is described in detail hereinafter.

The output signals of the charging means 14 which represent increments of X-axis deflection, namely, the outputs of the positive X-axis charging circuit 29 and the negative X- axis charging circuit 31, are accumulated in a storage capacitor 16. Each incremental signal is a constant current pulse ofa predetermined duration; i.e. an increment of charge. Similarly, the output of the charging means 14 representing increments of Y-axis deflection, namely the outputs of the positive Y-axis charging circuit 32 and the negative Y-axis charging circuit 33, are applied to a storage capacitor 17. A clamp circuit 35 operates at the end of the generation of each character to clamp the voltage on each

storage capacitor

16, 17 to a starting or reference level before beginning the generation of the next character. The charge accumulated in each of the respective storage capacitors l6 and 17 is equal to the sum of the increments of charge applied thereto from the charging means. The voltage across each capacitor is proportional to the charge stored therein, and the capacitor voltages are applied across the X-axis and Y-

axis deflection plates

18 and 19, respectively, in the cathode-ray tube 21. The cathode-ray tube 21 is also provided with a beam position deflection yoke 34 for positioning the traced characters at a desired region of the cathode-ray tube screen 36.

During the generation of some characters on the cathoderay tube screen 36, certain sections of the character may have to remain unlighted or blanked, In the illustrated cathode-ray tube 21, the electron beam is produced by a cathode 37, and is directed to the screen 36 by suitable accelerating elements, not shown. A grid 38 is provided for controlling the intensity of the beam, and suitable changes in bias may be produced on the grid to blank or unblank the electron beam as desired. Such changes in grid bias are produced by an intensity circuit 39, coupled to the grid 38, As previously mentioned, the intensity circuit is controlled for blanking and unblanking the beam for those characters which so require it by means of a third wire in the set of wires l3, Trigger pulses produced in the third wire are applied through a gate 26 to the intensity circuit 39 to control operation thereof.

Where the character generator is operated as a dot-type generator. eam position is changed very quickly while blanked, and the beam is then unblariked while stationary to produce a dot on the screen 36 at a desired position. The characters are thus formed by a plurality of closely spaced dots, Under such o eration, the intensity circuit 39 provides periodic unblaiilt signals to the cathode-ray tube grid 38, which are spaced and which are of a length such that the beam is unblanked at the successive positions to which the beam is deflected. Where a blank space is necessary in a character, the pulses produced in the third wire are utilized in the intensity circuit to prevent an unblanking output from being applied to the grid 38, thus leaving the beam blanked in those positions. Details of circuitry for accomplishing the foregoing functions are shown in FIG. 7 and art; described below.

Where the character generator of FIG. I is operated as a stroke-type generator, the intensity circuit 39 provides a con tinuous bias n the grid 38 to maintain the beam unblanked at all times except during the times that blank sections are required; cg. to prevent tracing the same stroke twice. The output signals for stroke-type generation from the charging means i4 are igiinstant currents which continue for the full period of each stroke, The accumulation of charges in the storage capacitors during each period results in ramp-type voltage signals which thereby cause the characters to be generated by a series of lines or strokes produced on the screen 36 iii the cathode-ray tube 21. In the event a segment of a character is to be blanked, the appropriate pulses produced in the third wire of the set are applied through the gate 26 and are utilized by the intensity circuit to change the bias or the grid 33 to blank the cathode-ray tube beam. Details oi tt rllultl'y for accomplishing the foregoing functions are shown in FIG 16 and are described below.

Some cl'iaracters, when properly proportioned, require larger or iil liill ii' rements in one axis than in the other axis, or a larger or am i r dimension in width or height than other characters, i nosicAlI'ilClCfS requiring a change in proportion from the standard tililf'ii ll tr size are affected by the proportioning circuit M which is energized by the character selec tion logic circuit :it th same time the character is selected. The proportioning circuit is so constructed to enlarge or diminish the dimension of the character being generated along the X-aizts or the Y .i iris, depending upon which is appropriate, by the subtraction or addition of a suitable amount of capacitance iii the storage provided by the

capacitor

16 or 17. The proportioning circuit is also connected to the intensity circuit 39 lor reasons explained below. Details of circuitry which may hi. used as the proportioning circuit are shown in FIG. 8 and FIG. 9 and are described below,

OPERA-Phi A S DOT-TYPE GENERATOR Referring now to NUS. 2 and 3, an example of operation of the character manor of PEG. 1 as a dot'type character generator will be described in connection with the production of the capital etter (1 Fit]. 2 illustrates the appearance of the letter G on thrcath e ray tube screen, the numbers denoting the sequence FL. the various dots are formed. The maximuni number i. it its wi h which a character may be formed corresponds ii; iii; number oi cores 11 (FIG, 1) utilized for providing appropriate signals. in the illustration, 1"! dot positions are slip i. such as may be the case in a character generator using ll cores, the last core providing a stop or reset pulse. Graph A. of H6. 3 indicates the available pulse times and Graphs B and C indicate the possible pulses utilized, and the polarity of pulses utilized, in the X-axis and Y-axis wires, :espcctiveiy As previously mentioned, the generation ofa pulse and its polarity is determined by the winding of the wires on the cores.

The dots I through 5 in FIG. 2 are formed by varying the Y- axis deflection voltage while holding the X-axis deflection voltage constant. This may be seen by comparison of Graphs D and E in FIG. 3. The step voltage characteristic is achieved by suitable short duration constant current output signals such as may be produced in a blocking oscillator. and by feeding such signals to the storage capacitors l6 and 17. The constant current output signals are fed to the storage capacitors for a fixed, predetermined time which is much shorter than the intervals between steps. The time is established by the blocking oscillator period and may, for example, be about 0.2 microsecond. Thus, the time required to move the beam from one dot position to the next is about 02 microsecond. The period for sequential energizations of the cores may bit set at about 0.7 microsecond, and thus the beam may be left on for the remaining 0.5 microsecond to define a bright dot on the target screen. This is indicated by the Graph F. showing the production of successive intensity signals.

After illumination at the dot position 5 of FIG. 2, Xaxis deflection begins to direct the beam to the

positions

6, 7, 8 and 9. During the changes between the

positions

6, 7 and 8, no change in Y-axis deflection voltage occurs, as may be oh served from the graphs. Between

positions

9 and 11, no change in X-axis deflection occurs, while the Y-axis deflection voltage decreases in stepwise manner through the application of negative constant current signals to the storage capacitor. The production of dots l0 and 11 is prevented by the genera tion of a blanking pulse in the third wire indicated in the Graph G of FIG. 3. This causes the unblank output from the intensity circuit as indicated by the Graph F to be absent during periods I0 and 11 so the beam remains blanked at

posi tions

10 and 11. The beam is unblanked for position 12 and succeeding positions by the production of the next succeeding pulse in the third wire. At the dot 12 a slight inward excursion of the beam is produced by reducing the XSIXIES deflection voltage accordingly, indicated in the graphs The remainder of the character is traced out as indicated by a comparison of the deflection voltages in the Graphs D and E, and the intensity signals in the Graph F.

Referring to FIG. 4, the illustration at A intlitzilts the dot sequence followed in forming the character y when the incremerits of X-deflection and Y-deflection are equal. it may be seen that a pair of 45 slope lines results, the angle between the two sections ofthe V is and a disproportionate ra io of width to height of the character results. This is avoided by operation of the proportioning circuit 41 (FIG I) which will be described in detail below. Because of the opera ion of the proportioning circuit, the actual appearance of the letter on the screen of the cathode-ray tube is as in FIG. 48. thus being properly proportioned.

In FIG. 5, circuitry is illustrated which may be employed in the character generator of the invention for operating it as a dot-type character generator. Only circuitry for the generation of the X-axis deflection voltage is illustrated, however, it is to understood that the circuitry for generation of the Y-axis deflection voltage is similar. The character seicction logic 22 includes a plurality of selection circuits, each comprising a pair of resistors 42 and a capacitor 43 connected to a common junction 45, to which one end of each wire in an associated set is also connected. The capacitor 43 is grounded and the resistors are connected to individual input points 44., to which the remaining portion, not illustrated, of the character selection logic 22 is connected.

The remaining unillustrated portion of the character selec tion logic 22 may be any suitable circuit which will bring both input points 44 to a positive potential (for exam le, +5 volts each) when that particular character is selected, and which will maintain either a zero voltage on both of th input points, or a positive voltage on one and a zero voltage on the other, when that particular character is not to be selected, The results of the foregoing described voltage conditions will be set forth below. One particular satisfactory form of character selection logic may provide a character repertory of 64 characters, selected by six binary coded signals (six bits in parallel). As is known in the art, the six bits can be combined to produce 64 possible signals (2). Combining may be done in two stages, a first stage dividing the six bits into two groups of three each. Each group of three can be combined into eight possible combinations in the first combining stage. The 16 signals (two groups of eight) may be then combined to produce 64 unique signals, in the second combining stage, by means of 64 selection circuits, each consisting of a pair of resistors and a capacitor as described in connection with the resistors 42 and the capacitor 43. When the six binary signals of the character selection logic are set to select the character represented by the selection circuit having input points 44, one signal in each group of eight will be positive (the one con nected to point 44 of the selected circuit), and the other seven in each group at 0. Thus, only one of the 64 selection circuits will have both inputs at positive potential, the other 63 having either both inputs at volts or one input at a positive voltage and the other at 0 volts.

The opposite ends of the wires in each set are connected to the

gates

23, 24 and 26, respectively. The gate 23 consists of a plurality of diodes 46 (64 diodes for 64 characters are used with character selection logic of the type described in the example, above), the outputs of the diodes being tied together and coupled to the X-axis pulse detector 27. The X-axis pulse detector 27 includes a transistor 47 having a collector connected through a resistor 48 to a source of potential. The collector is also connected through a capacitor 49 to ground. When a character is selected, its selection junction 45 rises to a positive potential; e.g. volts. The particular one of the diodes 46 connected to the wire of the selected character is forward biased by the character selection logic 22 and causes the base of the transistor 47 to rise nearly to the positive potential of the selection circuitjunction 45 to which it is connected. The transistor, under such conditions, is biased well into conduction. All of the other selection circuits are placed, by the character selection logic 22, in a condition such that the voltage at the particular selection junction is at either 0 or one-half that at the junction in the selected selection circuit; e.g. at 0 volt or volts. At such voltages, the other diodes in the gate 23 are back biased; e.g. each diode has its cathode at nearly +5 volts and its anode at either 0 volt or +2.5 volts. With the transistor 47 biased well into conduction due to the biasing above described, pulses produced in the coding wire are passed by the associated diode. Such pulses may be positive or negative with respect to the bias level, depending upon the way the wire is wound on the cores. A pulse on a selected wire which occurs when a given core ll is energized is positive if the wire is wound on that core in one sense, and negative if wound in the other sense. The pulses on the selected wire cause the transistor to produce pulses of corresponding polarity superimposed on its steady output resulting from the bias voltage. The emitter of the transistor 47 is connected through a resistor 52 and parallel capacitor 51 to a winding 53 which surrounds a portion of a magnetic core 54. The magnetic core 54 has a pair of output windings 56 and 57 which produce output pulses in response to pulses in the winding 53.

A satisfactory series of pulse configurations may be achieved by designing the sequential pulse generator 12 to produce square wave pulses of, for example, 0.6-microsecond duration. At the end of the 0.6-microsecond period, a sharp 0.2-microsecond overshoot pulse is utilized to trigger the next succeeding stage in the sequential pulse generator. A circuit for accomplishing this is illustrated in FIG. 6 and is described in detail subsequently in this specification. The resulting form of trigger pulses produced in the wires wound on the energized cores, such pulses being amplified by the transistor 47, are indicated adjacent the resistor 52in Fit]. 5. Depending upon the direction in which the wire is wound on a particular core, either the upper pulse or lower complementary pulse is produced upon the energizing of that core.

When the core 54 is energized by trigger pulses of such illustrated configuration, output pulses are produced in the windings 56 and 57 of a configuration as indicated in circles adjacent the core 54. A positive X-axis deflection pulse (the upper pulse adjacent resistor 52) applied to the winding 53 produces a pulse in the winding 56 having the configuration of the upper one of the two circled pulse forms. At the same time a pulse in the winding 57 is generated having the configuration of the lower of the two circled pulse forms shown. The opposite is true upon application of a negative X-axis deflection pulse (the lower pulse adjacent resistor 52) to the winding 53.

The winding 56 is connected across the base and emitter of a PNP transistor 58 through a capacitor 59. The transistor 58 is a pulse amplifier for driving the positive X-axis charging circuit 29. A biasing network comprised of

resistors

61, 62 and 63 is provided, coupled to a suitable source 60 of positive potential, and is designed to bias the transistor 58 near cutoff. The winding 57 is connected to a pulse amplifier including a transistor 58a for driving the negative X-axis charging circuit 31, which is identical with that of the positive X-axis charging circuit 31. Since both pulse amplifiers are PNP transistors, they trigger only on negative pulses applied to their bases. Thus, each time the core 54 is pulsed, only one of the two output pulses in the respective windings 56 and 57 will be of a polarity to trigger the associated pulse amplifier transistor. The particular transistor which is triggered thereby depends on the polarity of the pulse in the winding 53.

The collector of the transistor 58 is grounded through a resistor 64, and provides an output pulse to the positive X-axis charging circuit 29, when a positive pulse is received by the gate 23 from a wire 13. The collector of the transistor 58a provides an output pulse to the charging circuit 31 when a negative pulse is received by the gate 23, in a similar manner.

In the charging circuit 29, the pulse from the transistor 58 is coupled through a capacitor 66 to the base of an NPN transistor 67. The base of the transistor 67 is grounded through a resistor 68 and a parallel connected diode 69. The transistor 67 is connected as a blocking oscillator, having a collector winding 71 with a parallel resistor 72 and having an emitter winding 73. A pair of

resistors

74 and 76 connect a source 70 of positive potential to ground and the coil 73 is connected to the juncture between such resistorsv The coil 7] is connected to a further source 75 of positive potential, and the

coils

71 and 73 have a common core. Thus, the blocking oscillator is emitter coupled and provides a constant voltage output pulse in the secondary winding 77.

The secondary winding 77 is connected to provide a potential difference to the base-emitter circuit of a constant current NPN transistor 78. The transistor 78 has its base connected to one end of the winding 77, and its emitter connected through an emitter resistor 79 to the other end of the winding 77. The constant current output of the transistor 78 is coupled to the storage capacitor 16. The collector of the transistor 78 is connected to a source 80 of positive potential which is higher than the maximum deflection voltage to be produced across the X- axis deflection plates of the cathode-ray tube.

The first stage of the negative X-axis charging circuit 31 is identical with the first stage of the positive X-axis charging circuit 29 and similar parts are indicated with the same reference numeral and the subscript a." The blocking oscillator of the negative X-axis charging circuit 31 operates to provide a constant voltage output signal by producing a signal of appropriate duration in the output winding 81 of the blocking oscillator. The output stage of the negative X-axis charging circuit includes a constant current transistor 82 having a current-determining emitter resistance consisting of a fixed resistor 83 and a variable resistor 84 connected to ground, and having its collector coupled to the storage capacitor 16. Thus, both the positive and negative incremental changes in the X- axis deflection voltage are determined by means of constant positive or negative currents fed to the capacitor for a fixed time predetermined by the time period of the blocking oscillator in the charging circuits.

Referring now to H6. 6, one type of stage which may be incorporated in the sequential pulse generator 12 is illustrated. Such a pulse generator stage is capable of producing the square-wave-with-overshoot pulses previously described. It is to be understood, however, that the invention is not limited to the use of such a type of pulse generator or pulse configuration. Only one stage is shown in FIG. 6 and will be described, since it is to be understood that all stages are identical. A positive going signal from the next preceding stage or from a suitable start pulse circuit, not shown, is applied at the terminal 86. The terminal 86 is connected through a differentiating circuit including a capacitor 87 and a resistor 91. A diode 88 couples the differentiated signal to the base of an NPN transistor 89, the emitter of which is coupled through a resistor 92 to ground. The base of the transistor 89 is also coupled to ground through one winding 93, a feedback winding of a blocking oscillator transformer. The other winding 94 of the transformer is connected to the collector of the transistor and to a suitable source of positive potential 95. The winding 94 is also connected across a further winding 96 through a resistor 97 and a diode 98. The further winding 96 is wound on the associated core 11, upon which are also wound the wires 13. The collector of the transistor 89 is also connected to the next succeeding stage. The foregoing circuitry thereby operates as a base coupled blocking oscillator, providing output pulses to energize the associated core 11, and to also trigger the next succeeding stage.

When the transistor 89 is triggered into conduction by a positive input signal applied to its base, the collector current through the winding 94 increases, and the collector voltage drops. By the coupling of the transformer. the winding 93 drives the base further in the positive direction, causing a rapid regenerative decrease in the collector voltage until the collector voltage bottoms at substantially the emitter voltage of transistor 89. Current increases in the winding 94 thereafter, at a rate determined largely by the winding inductance and the supply voltage at terminal 95. When the transformer core becomes saturated (e.g. after 0.6 used), increasing current in winding 94 can no longer maintain a positive voltage on the base of transistor 89, and the regenerative on" action stops. The base then returns toward potential, which causes the collector current to be reduced, which drives the base further negative, so that collector current is rapidly cut off by a regenerative "off" action. The sudden interruption ofcollector current causes a positive going voltage step at the collector. Since the energy stored in the core of the transformer during the 011" interval of the blocking oscillator must be dissipated, the voltage at the collector overshoots, or wings to a potential more positive than the terminal 95, and current is forced to flow through the diode 98, the winding 96 and the resistor 97. Part of the energy stored in the blocking oscillator transformer core thus is transferred to the core 11, magnetizing it and producing the desired information pulses in the wires I3, while another part is dissipated in the resistor 97. The time constant of the overshoot interval of the period is made small, by choosing a low value for resistor 97, so the pulses generated in wires l3 are short, e.g. about 0.] psec.

During the on interval of the transistor 89, a signal is generated across resistor 92, which is proportional to emitter current. This signal is a ramp voltage superimposed on a pedestal, and is coupled to terminal 99, The signals at terminal 99 in the first and last blocking oscillators of the sequential pulse generator 2 are used in the intensity circuit 39, as will be explained h reafter, while the terminals 99 in the intervening stages are not used.

The positive going step in the collector voltage at the end of the on interval of the transistor 89 is coupled to the input trigger terminal 86 ofthe next stage, to initiate its action.

An intensity circuit, which may be utilized in the character generator of HG I when the character generator is operated as a dot-type character generator, is illustrated in FIG. 7. The circuit includes a flip-flop comprised of a pair of NPN transistors l0! and HI? connected in appropriate fashion by a plurality of resistors, capacitors and diodes. The emitters of

transistors

101, 102 are connected to a source of positive potential +V1, while the collectors are coupled to a more positive potential +V2. Ground potential can then be coupled to the bases through suitable bias resistors. An initiating signal from the emitter circuit (terminal 99) of the first stage in the sequential pulse generator 12 (FIG. 1) is applied to the unblank terminal 103 of the intensity circuit (FIG. 7). The initiating signal is applied to the base of one transistor 102 of the flip-flop through a capacitor 104 and a steering diode 106. When the first sequential pulse generator stage pulses, its emitter output signal sets the flip-flop to provide an output signal through a series resistor 107 to a buffer amplifier in cluding an NPN transistor 108. The output signal provided through a resistor I09 from the transistor 108 is a s uare wave having substantial length, rather than a short pulse, and serves to enable or disable an unblank blocking oscillator which provides intermittent signals for unblanking the cathode-ray tube beam at appropriate times. The blocking oscillator is emitter coupled and includes an NPN transistor 11] having an emitter winding 112 and a collector winding 113. The emitter winding is connected to the resistor 109, and also to a source of positive potential through a resistor 110. The collector winding 113 is connected to a source 105a of positive potential which is higher than the source 105. A series connected diode 115 and damping resistor 1I4 are connected in parallel with the winding 113.

In order to trigger the blocking oscillator (provided it is in the enabled condition) each time the cathode-ray tube beam has been stepped to a new position by the charging

circuits

29, 31, 32 or 33, (FIG. 1), output signals from the charging cir cuits are connected through an OR gate consisting of four diodes 116. The output signals are obtained from the emitter circuits of the charging circuit blocking oscillators; e.g trr minals 75, 85 in FIG. 5. The diodes 116 are slightly back biased by a source 117 of positive potential connected to their cathodes through the parallel combination of a resistor H8 and a capacitor 119. At each timing interval (see Graph A, FIG. 3) a pulse will be passed by the OR gate diodes 1 I6, since a pulse sufficient to overcome the hack bias is present in at least one of the four charging circuit outputs. This pulse is applied to the base of the transistor 11] through a resistor 121 and parallel capacitor 122. The pulse applied to the base of the transistor is a positive going pulse and triggers the blocking oscillator (providing it is in the enabled condition). A pulse is therefore produced in the output winding 124 of the blocking oscillator.

The pulse produced in the output winding E24 is coupled across the emitter and base of a PNP Quip-.1! transistor I26 through a resistor [27. The output of the transistor I26 is developed, from a source 125 of positive potential tied to the emitter, across a load resistor 128 in the collector circuit and applied to the cathoderay tube grid. The circuitry may be designed such that the blocking oscillator produces a negative going rectangular pulse nominally about 0.3 microsecond in width and 9 volts in magnitude at the collector of the transistor 111, with a positive overshoot lasting about 0.3 #sec. following its trailing edge A wave of the same shape, but inverted and about one-quarter of the magnitude (assuming a turns ratio of nine turns on the collector winding 113 and two turns on the output winding 124) appears at the upper end of the output winding and couples to the base of the output transistor [26. The output transistor is normally off (at t) bias) and is turned farther off by the positive rectangular pulse (dur ing the transition time between spot positional. During the overshoot time ofthe blocking oscillator, the output transistor 126 clips and amplifies and inverts the negative overshoot, producing a short positive unblank pulse at its collector. This pulse is applied to the grid of the cathode-ray tube for unblanking the beam.

The circuit of FIG. 7 represents a simple embodiment of the intensity circuit 39 which can be used in the character generator of FIG. 1. By the use of alternative inlwuisi y ircu ts in which the blocking oscillator is replaced by a combination of two blocking oscillators in cascade, the delay period and unblank period can be controlled independently. The delay period to allow for transition of the spot can be reduced to 0.2 used, or any other desired interval by proper design and adjustment of the first blocking oscillator. The unblank interval can be increased to 0.5 sec, or any other desired interval, by proper design and adjustment of the second blocking oscillator, as is well known in the art.

The flip-flop 101-102 is placed in the reset or disabling condition, as described below, when certain dots are not to appear on the cathode-ray tube screen. (The reset condition corresponds to conduction of transistor 101). When the flip-flop is disabled. the buffer amplifier transistor 108 conducts heavily from the positive voltage source at its collector through the resistor 109 and the further resistor 110 to the lower potential source 105 to which the resistor 110 is connected. The current through the resistor 110 causes the blocking oscillator transistor 11] emitter to rise to a substantially more positive potential than its base. Hence, triggering of the blocking oscil lator by pulses from the diodes 116 is prevented.

In the illustrated circuit, the flip-flop 101,102 is controlled by blank and unblank pulses produced in the third line or wire. Such pulses are applied through the OR gate 26 to a twostage amplifier. The two-stage amplifier is comprised of a pair of

NPN transistors

131 and 132 connected by suitable biasing tesistors and capacitors respectively in an emitter follower configuration and a grounded emitter configuration. Such pulses are applied to the flip-flop comprising the

transistors

101 and 102 through a capacitor 133, and also through a capacitor 136. The first pulse (see FIG. 3 G) operates the flip-flop to the reset or disabling condition, causing the buffer amplifier to disable the blocking oscillator. The second pulse sets the flipflop again to a condition wherein the buffer-amplifier enables the blocking oscillator. In addition, an unblank inhibit pulse is applied to a terminal 138 by the last stage of the sequential pulse generator 12 (FIG. 1). This pulse is applied to the flipflop through a capacitor 139 and operates the flip-flop to the reset or disabling condition when the generation of a character is completed. Thus, the cathode-ray tube beam is blanked until such time as generation of a new character begins and a pulse is applied to the terminal 103.

By utilizing the flip-flop consisting of the

transistors

101 and 102, it is possible to generate many types of characters without the necessity of a third wire being threaded through the cores 11. Thus, if no portions of a character are to be blanked or retraced, it is unnecessary to inhibit the output of the blocking oscillator. If the character shape requires a blanked portion or a retraced portion, the third wire need only be threaded through two cores for each blanked segment, rather than threaded to provide blanking pulses for each beam position. Thus, the first pulse produced in the third wire resets the flip-flop (which is initially set upon the production of a pulse in the first core 11) and the second pulse produced sets the flip-fiop once again to a condition for enabling the blocking oscillator.

The unblank pulse applied by the first sequential pulse generator to terminal 103 and unblank inhibit pulse applied by the last sequential pulse generator to terminal 138 are not both required for operation of the character generator. If the inhibit pulse at terminal 138 is omitted, it is necessary to thread the third wire 13 to generate an additional pulse to blank the cathode-ray tube beam after the last desired dot is produced. Conversely, the unblank pulse to tenninal 103 can be omitted if the third wire 13 is threaded to generate an additional pulse before the first desired dot is produced.

As an alternative intensity control method, the third wire 13 may be threaded to produce positive pulses when it is desired to unblank the beam and negative pulses when it is desired to blank the beam. The intensity circuit in that event is accordingly modified to include a pulse detector and separator like transistor 47 and core 54 (FIG. with its windings 53, S6, 57. The separated pulses from the two output windings of the core are then used respectively to set and reset the intensity flip-flop via separate steering diodes.

As a further alternative, the intensity circuit 39 may be modified to operate without the flip-flop and without the OR gate comprised of the diodes 116. Under such circumstances, the third wire for each character is threaded through a core for each dot to be brightened. The pulses produced in the third wire are then coupled, by suitable amplification, directly to the input of the blocking oscillator.

FIGS. 8 and 9 illustrate enlarging and diminishing circuits, respectively, which may be utilized as the proportioning circuit 41 in FIG. 1. Two enlarging circuits and two diminishing circuits, one for each for each axis, may be provided. Satisfactory operation is possible with only one proportioning circuit per character generator, however. In the enlarging circuit of FIG. 8, a diode 141 (FIG. 8) is used for each character to be enlarged, and is connected to the input resistor junction 45 for that particular character in the character selection logic 22. The plurality of diodes 141 are arranged to form an OR gate and function in a manner similar to the OR gates for the charging means and for the intensity circuit. If a character is selected which requires enlargement, a signal (e.g. +5 v.) is passed by the associated one of the diodes 141 to the base of a first of a pair of

NPN transistors

142 and 143 having a common emitter resistor 144 connected to ground. The base of the first transistor 142 is also connected to ground through a resistor 146, and the base of the second transistor 143 is connected to ground through a resistor 147. The base of the second transistor 143 is also connected through a resistor 148 to a source of positive potential. The

resistors

147, 148 form a voltage divider which bias the base of the second transistor 143 to a suitable positive potential; e.g. +2.5 volts. The collector of the first transistor 142 is also connected to a source of positive potential. Without any positive signal being passed by any of the diodes 141, the first transistor 142 is biased off and the second transistor 143 is biased on.

A capacitor 149 is connected between the collector of the second transistor 143 and the

storage capacitor

16 or 17 for the axis to be enlarged. The capacitor 149 is normally (Le. when the second transistor 143 is biased on) in the system and effectively in parallel with one of the

capacitors

16, 17; however, when a sufficiently positive signal; e.g. +5 v., is passed by one of the diodes 141, the first transistor 142 is rendered conductive, cutting off the second transistor 143 and, in effect, removing the capacitor 149 from the systemv Accordingly, less storage capacity is present, producing an enlargement of the character.

Referring now to the diminishing circuit shown in FIG. 9, an OR gate comprised of a plurality of diodes 151 receives signals from the input resistor junctions 45 for those characters to be diminished, which input junctions are in the character selection logic 22. The base of an NPN transistor 152 is connected to the diodes 151 through a resistor 153. The base of the transistor 152 is also connected through a resistor 154 to a source of negative potential, and the emitter is grounded. Accordingly, the transistor is normally biased to an off condition. In the presence of a sufficiently positive signal passed by one of the diodes 151, however, the transistor 152 is rendered conductive. A capacitor 156 is connected between the collector of the transistor 152 and the

storage capacitor

16 or 17 associated with the particular axis to be diminished (normally the X-axis). Accordingly, when the transistor 152 is rendered conductive, the capacitor 156 is added to the system effectively in parallel with one of the

capacitors

16, 17, resulting in a diminishing of the character on the associated axis.

The theory of operation of the enlarging and diminishing circuits is explained by the physical laws of electrical charge. Charge (in coulombs) is equal to the product of time (in seconds) and current (in amperes). If current varies during the interval of time in which it flows, charge is the integral of current over the time interval; i.e.

Claims

1. For use with a cathode-ray tube having X- and Y-axis deflection means for producing beam deflections parallel to X and Y axes to describe a character, a character generator comprising, a plurality of magnetic cores, means for sequentially energizing said cores one at a time, at least one set of wires for producing information to generate a predetermined character, at least one wire of which is wound on selected ones of said cores to produce, upon energization of said cores, a sequence of pulses representative of incremental changes in beam deflection, charging means, means connecting said wires to said charging means, said charging means being responsive to the pulses produced in said wires to produce constant current output signals each corresponding to an increment of X- or Y-axis deflection, and first and second storage means connected to said charging means for receiving the X-axis constant current output signals and the Y-axis constant current output signals, respectively, said first and second storage means thereby each producing a deflection voltage corresponding to the sum of the charging means output signals representing increments of deflection in the respective axis, said first and second storage means being adapted for connection to the X- and Y-axis deflection means, respectively, to apply deflection voltage thereto.

2. A character generator according to claim 1 including an intensity circuit adapted for connection to the electron gun of the cathode-ray tube for blanking and unblanking the cathode-ray tube beam in response to intensity control pulses applied to said intensity circuit, wherein said at least one set of wires includes at least one wire wound on selected ones of said cores tO produce intensity control pulses for the predetermined character upon energization of said cores, wherein said charging means are adapted to produce output signals which are substantially shorter in duration than the time between energizations of successive magnetic cores, and wherein said intensity circuit is adapted to produce unblank signals during the period said charging mans are off, said character generator thereby producing characters defined by a series of dots.

3. A character generator according to claim 1 wherein said charging means are adapted to produce output signals which are substantially equal in duration to an integral multiple of the time period between energizations of successive cores, for defining characters by means of line segments.

4. A character generator according to claim 1 wherein each of said storage means comprises a capacitor.

5. A character generator according to claim 1 including a plurality of sets of wires, one set for each character to be generated, wherein the means connecting the wires to the charging means comprise selecting switch means between each set of wires and said charging means, and wherein means are provided for selectively closing said selecting switch means to select characters for generation.

6. A character generator according to claim 1 wherein at least one of said storage means comprises a capacitor, wherein diminishing means are provided including a further capacitor and diminishing switch means selectively coupling said further capacitor in parallel with said capacitor in said one storage means, and wherein means are provided to selectively close said diminishing switch for a time interval sufficient to generate one character; thereby to diminish the character in at least one axis.

7. A character generator according to claim 1 wherein at least one of said storage means comprises a pair of capacitors, and wherein enlarging switch means are provided to selective disable one of said pair of capacitors in said one storage means, and wherein means are provided to selectively open said enlarging switch means for a time interval sufficient to generate one character, thereby to enlarge the character in at least one axis.

8. A character generator according to claim 1 wherein one wire in at least one set is wound on a magnetic core following the last magnetic core used for generation of the character associated with that set, and wherein means are provided responsive to production of pulses in said one wire for stopping further sequential energization of said cores.

9. A character generator according to claim 1 wherein said wires in each of said sets are wound on the cores to produce a binary code representative of incremental changes in beam deflection in both X and Y axes upon energization of each core, and wherein said charging means include a binary code converter for decoding said binary codes and initiating production of constant current output signals corresponding thereto.

10. A character generator according to claim 1 wherein each set contains at least two wires, one wire defining X-axis deflections and the other wire defining Y-axis deflections.

11. A character generator according to claim 1 wherein each set contains at least four wires, two wires defining first and second orders of magnitude of X-axis deflection, respectively, and the other two wires defining first and second orders of magnitude of Y-axis deflection, respectively.

12. A character generator according to claim 1 wherein a first wire in each set is wound upon selected ones of said cores to produce upon energization of said cores, a first sequence of pulses of uniform amplitude, each pulse representing an incremental change in beam deflection on one axis; a second wire in each set is wound upon selected ones of said cores to produce, upon energization of said cores, a second sequence of pulses of uniform amplitude, each pulse representing an incremental change in beam deflection in the other axis; And said charging means comprise a first charging means responsive to pulses produced in said first wire of each set and providing output signals to said first storage means, and a second charging means responsive to pulses produced in said second wire of each set and providing output signals to said first storage means.

13. A character generator according to claim 12 wherein said first wire in at least one set is wound to produce a first sequence comprising both positive polarity and negative polarity pulses; said second wire in at least one set is wound to produce a second sequence comprising both positive polarity and negative polarity pulses; and each of said charging means is adapted to produce constant current output signals of one polarity in response to positive pulses and constant current output signals of the other polarity in response to negative pulses; whereby positive increments of deflection are produced by pulses of one polarity and negative increments of deflection are produced by pulses of the other polarity.

14. A character generator according to claim 12 including an intensity circuit coupled to the electron gun of the cathode-ray tube for providing intensity control signals to the gun in response to intensity control pulses; wherein a third wire in at least one set of wires is would upon selected ones of said cores to produce, upon energization of said cores, a third sequence of pulses, said third sequence of pulses being representative of the intensity variations required to generate the character; and the pulses in said third sequence are coupled from said third wire via said connecting means to said intensity circuit; whereby the pulses in said third sequence control the intensity of the cathode-ray tube.

15. A character generator according to claim 12 wherein said charging means are adapted to produce output signals which are substantially shorter in duration than the time between energizations of successive magnetic cores, and wherein said intensity circuit is adapted to produce intensifying signals during the period said charging means are off, said character generator thereby producing characters defined by a series of dots.

16. A character generator according to claim 12 adapted to generate signals describing a selected one of a plurality of characters, comprising: a plurality of selection terminals, one terminal being provided for each of the plurality of characters; means to selectively apply a selection signal to one of the selection terminals for a time interval sufficient to generate one character, said one selection terminal being maintained by said selection means substantially above a predetermined threshold potential and the balance of said selection terminals being maintained by said selection means substantially below said threshold potential; a first deflection control terminal coupled to the input of said first charging means; and a second deflection control terminal coupled to the input of said second charging means; means biasing each deflection control terminal toward a reference potential, said reference potential being below said threshold potential; wherein one set of wires is provided for each of the plurality of characters; wherein said means connecting said wires to said charging means comprise said first and second deflection control terminals, said biasing means, and a plurality of diodes, one diode being provided for each wire; wherein a first end of every wire in each set is coupled to one of said selection terminals, said terminal being common to all the wires of the set; wherein the second end of each wire is coupled to the anode of one of said diodes; wherein the cathode of every diode coupled to the first wire of any set is coupled to said first deflection control terminal; and wherein the cathode of every diode coupled to the second wire of any set is coupled to said second deflection control terminal; whereby, every diode coupled to a wire of the set which is coupled to the selection terminal above tHe threshold potential is conductive and passes every pulse produced in the wire coupled thereto when said cores are sequentially energized; and every diode coupled to a wire of a set which is coupled to a selection terminal below the threshold potential is nonconductive and passes none of the pulses produced in the wire coupled thereto when the cores sequentially energized.

17. A character generator according to claim 12 adapted to generate signals describing a selected one of a plurality of characters, comprising: a plurality of selection terminals, one terminal being provided for each of the plurality of characters; means to selectively apply a selection signal to one of the selection terminals for a time interval sufficient to generate one character, said one selection terminal being maintained by said selection means substantially below a predetermined threshold potential and the balance of said selection terminals being maintained by said selection means substantially above said threshold potential; a first deflection control terminal coupled to the input of said first charging means; and a second deflection control terminal coupled to the input of said second charging means; means biasing each deflection control terminal toward a reference potential, said reference potential being above said threshold potential; wherein one set of wires is provided for each of the plurality of characters; wherein said means connecting said wires to said charging means comprise said first and second deflection control terminals, said biasing means, and a plurality of diodes, one diode being provided for each wire; wherein a first end of every wire in each set is coupled to one of said selection terminals, said terminal being common to all wires of the set; wherein the second end of each wire is coupled to the cathode of one of said diodes; wherein the anode of every diode coupled to the first wire of any set is coupled to the first deflection control terminal; and wherein the anode of every diode coupled to the second wire of any set is coupled to said second deflection control terminal; whereby, every diode coupled to a wire of the set which is coupled to the selection terminal below the threshold potential is conductive and passes every pulse produced in the wire coupled thereto when said cores are sequentially energized; and every diode coupled to a wire of a set which is coupled to a selection terminal above the threshold potential is nonconductive and passes none of the pulses produced in the wire coupled thereto when the cores are sequentially energized.

18. A character generator for providing signals describing a selected character to drive the X-axis deflecting devices and the Y-axis deflecting devices of a two axis graphical display, comprising: a plurality of magnetic cores; means for sequentially energizing said cores; a plurality of sets of control wires wound on said cores, at least one of said sets comprising at least one X-axis control wire wound on selected ones of said cores to produce a first sequence of pulses at uniform amplitude upon energization of said cores, and at least one Y-axis control wire wound on selected ones of said cores to produce a second sequence of pulses of uniform amplitude upon energization of said cores the winding of said X-axis control wire and said Y-zxis control wire upon said cores being a function of the shape of the selected character, said first sequence of pulses being representative of the sequence of X-axis deflections required to generate the selected character, and said second sequence of pulses being representative of the sequence of Y-axis deflections required to generate the selected character; first and second charging means each providing constant current output signals in response to receipt of pulses; gating means for passing pulses from the X-axis and Y-axis control wires of a selected one of said sets of control wires corresponding to the selected character to said first and second charging means, respectively; and first and second storage means, said first storage means being connected to receive and accumulate the constant current signals from said first charging means, and said second storage means being connected to receive and accumulate the constant current signals from said second charging means, said first storage means providing an output voltage signal representative of the X-axis deflections required to generate the selected character, and said second storage means providing an output voltage signal representative of the Y-axis deflections required to generate the selected character.

19. A character generator according to claim 18 comprising: an intensity circuit adapted to provide intensity control signals to the intensity control device of the graphical display in response to intensity control pulses; wherein at least one set of control wires includes at least one intensity control wire wound on selected ones of said cores to produce a third sequence of pulses upon energization of said cores, said third sequence of pulses being representative of the sequence of intensity variations required to describe the character; and wherein said gating means are operable to receive pulses from said intensity control wire and to provide pulses to said intensity circuit; whereby the pulses in said intensity control wire control the intensification of the graphical display.

20. A character generator according to claim 19 wherein: said charging means are adapted to provide constant current output signals each having a duration substantially equal to an integral number of said periods between successive core energization, and said intensity circuit is adapted to provide intensifying signals each having a duration substantially equal to an integral number of periods between successive core energizations, whereby the character is described on the graphical display as a plurality of sequentially connected straight line strokes.

21. A character generator according to claim 20 wherein: said charging means are adapted to provide constant current output signals, each beginning upon the receipt of a pulse from an associated control wire and ending upon the receipt of the next pulse from the same wire; and at least one wire of at least one set of control wires is wound to produce at least one pair of adjacent pulses spaced apart in time by an interval substantially equal to a plurality of the periods between successive core energizations; whereby the charging means receiving said pair of pulses produces an extended constant current signal with a duration of a plurality of the periods between successive energizations; and whereby the storage means receiving said extended constant current signal provides a deflection voltage without discontinuities during said interval.

22. A character generator according to claim 21 wherein: an X-axis control wire of at least one set of control wires is wound to provide at least one pair of adjacent X-axis pulses spaced apart by an X-axis interval substantially equal to a plurality of the periods between successive core energizations; a Y-axis control wire of the same set is wound to produce at least one pair of adjacent Y-axis pulses spaced apart by a Y-axis interval substantially equal to a plurality of the periods between successive core energizations; said X-axis interval and said Y-axis interval coincide in time for a plurality of the periods between successive core energizations; whereby a straight line segment is generated on the graphical display without discontinuities during the interval of coincidence.

23. A character generator according to claim 19 wherein: each pulse produced in an axis control wire represents a predetermined increment of deflection on the graphical display; each charging means provides a discrete constant current output signal in response to each pulse received from the associated control wire; each discrete constant current output signal has a duration substantially less tHan the period between successive energizations of the cores; each intensity control signal has a duration not more than the difference between the core energization period and the duration of the constant current signal; whereby the character id described as a pattern of sequential dots on the graphical display device.

24. A character generator according to claim 18 wherein: at least one of said storage means comprises a storage capacitor; proportioning means are provided comprising a further capacitor, proportioning switch means connected to selectively couple said further capacitor in parallel with said storage capacitor, and means is selectively actuate said proportioning switch means according to a dimension of the character to be described; whereby the dimension of the character generated on the graphical display in at least one axis is the smaller of two predetermined dimensions when said storage capacitor and said further capacitor are coupled in parallel, and the larger of the two predetermined dimensions when said capacitors are not coupled in parallel.

25. A character generator according to claim 18 wherein: one X-axis control wire in each set is wound to produce said first sequence of pulses; said first sequence of pulses comprises both positive polarity and negative polarity pulses; one Y-axis control wire in each set is wound to produce said second sequence of pulses; said second sequence of pulses comprises both positive polarity and negative polarity pulses; one Y-axis control wire in each set is wound to produce said second sequence of pulses; said second sequence of pulses comprises both positive polarity and negative polarity pulses; and said first and second charging means are each adapted to produce constant current output signals of one polarity in response to positive pulses and constant current output signals of the other polarity in response to negative pulses; whereby the sequence of X-axis deflections and Y-axis deflections required to generate the character are determined by said one X-axis control wire and said one Y-axis control wire.

26. A character generator according to claim 18 adapted to generate signals describing a selected one of a plurality of characters, comprising: a plurality of selection terminals, one terminal being provided for each of the plurality of characters; means to selectively apply a selection signal to one of the selection terminals for a time interval sufficient to generate one character, said one selection terminal being maintained by said selection means substantially above a predetermined threshold potential and the balance of said selection terminals being maintained by said selection means substantially below said threshold potential; a first deflection control terminal coupled to the input of said first charging means; a second deflection control terminal coupled to the input of said second charging means; means biasing each deflection control terminal toward a reference potential, said reference potential being below said threshold potential; wherein one set of wires is provided for each of a plurality of characters; wherein said gating means comprise said first and second deflection control terminals, said biasing means, and a plurality of diodes, one diode being provided for each wire; wherein a first end of every wire in each set is coupled to one of said selection terminals, said one terminal being common to all the wires of the set; wherein the second end of each wire is coupled to the anode of one of said diodes; wherein the cathode of every diode coupled to the X-axis control wire of any set is coupled to said first deflection control terminal and wherein the cathode of every diode coupled to the Y-axis control wire of any set is coupled to said second deflection control terminal; whereby, every diode coupled to a wire of the set which is coupled to the selection terminal above the threshold potential is conductive and passes every pulse produced in the wire coupled thereto whEn said cores are sequentially energized; and every diode coupled to a wire of a set which is coupled to a selection terminal below the threshold potential is nonconductive and passes none of the pulses produced in the wire coupled thereto when the cores are sequentially energized.

27. A character generator according to claim 18 adapted to generate signals describing a selected one of a plurality of characters, comprising: a plurality of selection terminals, one terminal being provided for each of the plurality of characters; means to selectively apply a selection signal to one of the selection terminals for a time interval sufficient to generate one character, said one selection terminal being maintained by said selection means substantially below a predetermined threshold potential and the balance of said selection terminals being maintained by said selection means substantially above said threshold potential; a first deflection control terminal coupled to the input of said second charging means; a second deflection control terminal coupled to the input of said second charging means; means biasing each deflection control terminal toward a reference potential, said reference potential being above said threshold potential; wherein one set of wires is provided for each of the plurality of characters; wherein said gating means comprise said first and second deflection control terminals, said biasing means, and a plurality of diodes, one diode being provided for each wire; wherein a first end of every wire in each set is coupled to one of said selection terminals, said one terminal being common to all wires of the set; wherein the second end of each wire is coupled to the cathode of one of said diodes; wherein the anode of every diode coupled to the X-axis control wire of any set is coupled to said first deflection control terminal; and wherein the anode of every diode coupled to the Y-axis control wire of any set is coupled to said second deflection control terminal; whereby, every diode coupled to a wire of the set which is coupled to the selection terminal below the threshold potential is conductive and passes every pulse produced in the wire coupled thereto when said cores are sequentially energized; and every diode coupled to a wire of a set which is coupled to a selection terminal above the threshold potential is nonconductive and passes none of the pulses produced in the wire coupled thereto when the cores are sequentially energized.

28. A character generator for providing signals describing a character to drive the X-axis deflecting devices and the Y-axis deflecting devices of a two-axis graphical display, comprising: a number N of magnetic cores; means for sequentially energizing said cores; at least one set of control wires wound on said cores, said set comprising M deflection control wires, each of the M wires being wound on selected ones of said cores to produce a coded sequence of pulses of uniform amplitude upon energization of said cores the winding of said deflection control wires upon said cores being a function of the shape of the character, whereby the M deflection control wires produce a sequence of N binary coded words each of M binary bits; gating means comprising deflection gating means connected to receive binary coded words from said deflection control wires; code converter means connected to receive binary coded words from said deflection gating means, and adapted to produce in response to said words at least one sequence of deflection control signals representative of the sequence of X-axis deflections required to generate the character and at least one sequence of deflection control signals representative of the Y-axis deflections required to generate the character; first and second charging means, said first charging means being connected to receive the sequence of X-axis deflection control signals from said code converter, and said second charging means being connected to receive the sequence of Y-axis dEflection control signals from said code converter said first and second charging means each providing constant current output signals in response to said deflection control signals; first and second storage means, said first storage means being connected to receive and accumulate the constant current signals from said first charging means, and said second storage means being connected to receive and accumulate the constant current signals from said second charging means, said first storage means providing an output voltage signal representative of the X-axis deflections required to generate the character, and said second storage means providing an output voltage signal representative of the Y-axis deflections required to generate the character.

29. A character generator according to claim 28 comprising: an intensity circuit adapted to provide intensity control signals to the intensity control device of the graphical display in response to intensity control pulses; wherein; least one set of control wires further comprises at least one intensity control wire wound on selected ones of said cores to produce another sequence of pulse upon energization of said cores, said other sequence of pulses being representative of the sequence of intensity variations pulses to generate the character; and said gating means include intensity gating means connected to receive pulses from said intensity control wire and to provide pulses to said intensity circuit; whereby the pulses in said intensity control wire control the intensification of the graphical display.

30. A character generator according to claim 29 wherein: said code converter means are adapted to produce deflection control signals each having a duration substantially equal to an integral number of the periods between successive core energizations; said charging means are adapted to provide constant current output signals each having a duration equal to the duration of the deflection control signal coupled thereto; and said intensity circuit is adapted to provide intensifying signals each having a duration substantially equal to an integral number of the periods between successive core energizations; whereby; the character is described on the graphical display as a plurality of sequentially connected straight line strokes.

31. A character generator according to claim 30 wherein: the code converter means are adapted to provide deflection control signals, each beginning upon the receipt of a binary coded word from the deflection control wires of a set and ending upon the receipt of a later binary coded word from the deflection control wires of the same set; the deflection control wires of at least one set of wires are wound to produce at least one extended deflection control signal extending over an interval substantially equal to a plurality of the periods between successive core energizations; whereby the charging means receiving said extended deflection control signal produces an extended constant current output signal with a duration of a plurality of the periods between successive energizations; and the storage means receiving said extended constant current signal provides a deflection voltage without discontinuity during said interval.

32. A character generator according to claim 31 wherein: the deflection control wires of at least one set of wires are wound to produce at least one extended X-axis deflection control signal extending over an interval substantially equal to a plurality of the periods between successive core energizations, at least one extended Y-axis deflection control signal extending over an interval substantially equal to a plurality of the periods between successive core energizations, said extended X-axis deflection control signal being coincident in time for a plurality of the periods between successive core energizations; whereby a straight line segment is generated on the graphical display without discontinuities during the interval of coincidence.

33. A character generator aCcording to claim 29 wherein: the code converter means are adapted to produce sequences of deflection control pulses; said charging means are adapted to provide constant current output signals each having a duration substantially equal to an integral number of the periods between successive core energizations; and said intensity circuit is adapted to provide intensifying signals each having a duration substantially equal to an integral number of the periods between successive core energizations; whereby: the character is described on the graphical display as a plurality of sequentially connected straight line strokes.

34. A character generator according to claim 33 wherein: the charging means are adapted to provide constant current output signals each beginning upon the receipt of a pulse from a sequence of deflection control pulses and ending upon the receipt of the next pulse from the same sequence; the deflection control wires of at least one set of wires are wound to produce at least one pair of deflection control pulses spaced apart in time by an interval substantially equal to a plurality of the periods between successive core energizations; whereby the charging means receiving said pair of pulses produces an extended constant current signal with a duration of a plurality of the periods between successive core energizations; and the storage means receiving said extended constant current signal provides a deflection voltage without discontinuities during said interval. 35 A character generator according to claim 34 wherein: the deflection control wires of at least one set of wires are wound to produce at least one pair of X-axis deflection control pulses spaced apart in time by an X-axis interval equal to a plurality of the periods between successive core energizations and at least one pair of Y-axis deflection control pulses spaced apart in time by a Y-axis interval equal to a plurality of the periods between successive core energizations, said X-axis interval and said Y-axis interval being coincident in time for a plurality of the periods between successive core energizations; whereby a straight line segment is generated on the graphical display without discontinuities during the interval of coincidence.

36. A character generator according to claim 28 wherein: at least one of said storage means comprises a storage capacitor; proportioning means are provided comprising a further capacitor, proportioning switch means connected to selectively couple said further capacitor in parallel with said storage capacitor, and means to selectively actuate said proportioning switch means according to a dimension of the character to be described; whereby the dimension of the character generated on the graphical display in at least one axis is the smaller of two predetermined dimensions when said storage capacitor and said further capacitor are coupled in parallel, and the larger of the two predetermined dimensions when said capacitors are not coupled in parallel.