US3587083A

US3587083A - Character generation and display system

Info

Publication number: US3587083A
Application number: US671317A
Authority: US
Inventors: Matthew P Tubinis
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1967-09-28
Filing date: 1967-09-28
Publication date: 1971-06-22
Anticipated expiration: 1988-06-22
Also published as: FR1582728A; GB1234580A; DE1774884B1

Abstract

A character generation and display system for characters comprised of a series of connecting line segments of various slopes which are formed by deflection waveforms resulting from integrating over a uniform period of time pulse trains having different frequencies.

Description

United States Patent Inventor Matthew P. Tubinis Penfield, N.Y.

App1.No. 671,317

Filed Sept. 28, 1967 Patented June 22, 1971 Assignee Xerox Corporation Rochester, N.Y.

CHARACTER GENERATION AND DISPLAY SYSTEM 5 Claims, 25 Drawing Figs.

US. Cl 340/324, 235/1S0.53 Int. Cl 606i 3/14 Field of Search 340/324. 1; 343/5 DP; 315/18, 19, 22; 328/127; 235/150.53, 150.51, 150.3

References Cited UNITED STATES PATENTS Burgett Roth et a1. Yanishevsky...

Primary Examiner-John W. Caldwell Assistant Examiner-Marshall M. Curtis AttorneysFrank A. Steinhilper, Ronald Zibelli and James J.

Ralabate IMO/324.1

ABSTRACT: A character generation and display system for characters comprised of a series of connecting line segments of various slopes which are formed by deflection waveforms resulting from integrating over a uniform period of time pulse trains having different frequencies.

PATENTED JUH22 I97! SHEET 1 OF 4 DISPLAY DEFLECTlON WAVEFORM GEN ERATOR CHARACTER CORE MATRIX DISTRI BUTER CHARACTER DECODER REG.

CLOCK ATTORNE Y5 PATENTEDJUNZZIQYI 3587,0823

SHEU 2 UF 4 FIG. 2A

/6 FIG. 28 20a 22a FI6.2C %ii iE':1

9 FIG. 20 6. FIG. 25

/8 FIG. 2F

..||ll .nl" 28a t FIG. 26 I 5 1 FIG 2H FIG 21 (We A TTORNE Y8 PATENTEDJUHZQIBYI 3,587,083

SHEET 3 OF 4 INTEGRA INVENTOR. FIG 4 MATTH' W R TUiNm A TTORNEYS PATENTEUJUNZ-ZIQYI $587,083

SHEET '4 OF 4 FIG. 5A FIG.5B FIG. 50 FIG. 50 F/G. 5D

FIG.5F FIG. 56 FIG. 5H FIG.5I FIG. 5/

FIG. 6A FIG. 63 FIG. 60

INVENTOR.

ATTH w P TL! IN BY Em A TTOI-PNEYS CHARACTER GENERATION AND DISPLAY SYSTEM This invention relates generally to character generation and, more specifically, to generation of a large number of alphanumeric symbols utilizing a plurality of line segments.

With the ever increasing use of high speed computers for the generation of data and other graphic communication, it is desirable to provide a high speed character generator which is capable of rendering a visual display of computer generated data and other graphic information. Any display system must be reliable as well as compatable with the speed of the data which it is designed to display. Electromechanical systems are no longer acceptable to the present computer environment for reasons of speed and mechanical complexity: Therefore, there exists a great need for a high speed electronic character generation and display system.

ltis an object of the present invention to provide an improved system which generates deflection and blanking voltage signals nece'ssary'tp control the display of various characters. 1

Another object of the present invention is to improve the generation of stroke-type characters for display by cathoderay tubes. I

These and other objects which may become apparent are accomplished in accordance with the principles of the present invention wherein a number of pulse generators having different frequencies are selectively coupled to an integrating circuit to provide a linear waveform of a slope and duration which is a function of the frequency of the pulses applied to the integrating circuit as well as the length of time of this duration.

These objects and other advantageous features of the present invention may be bitter understood from a reading of the following description when read in connection with the accompanying drawings wherein:

FIG. 1 is a block diagram of a character generator system in accordance with the principles of the present invention;

FIG. 2 A through I represent signal waveform diagrams helpful in understanding the manner in which the character of FIG. 2A is generated;

FIG. 3 illustrates a typical character core matrix which may be used in accordance with the principles of the present invention;

FIG. 4l schematically illustrates the deflection waveform generator in accordance with the principles of the present invention;

FIG. 5 A through 1 illustrate the various character segments which are used to generate a complete repetoire of characters using the principles of the pleseht invention; and

FIGS. 6A through C illustrate other characters which may be generated in accordance with the principles of the present invention.

Reference will now be made to FIG. 1 wherein a digital storage register 2 for the storage of character selection signals in accordance with the various conventional codes. The input to this register may be coupled to the output of a computer or other similar data generating or storage device. This storage register 2 has an output coupled to a conventional character decoder 4 which decodes the particular character code supplied by the digital register and selects a character set wire for that particular character which is threaded in the character code matrix 6. The exact nature of the character code matrix 6 will be described in more detail hereinafter in connection with FIG. 4.

FIG. I also shows a clock pulse source 8 which generates a train of pulses at a uniform pulse repetition frequency and supplies this pulse train to a suitable distributor 10 which, for example, may be a conventional ring counter. The outputs from the stages of this ring counter or distributor 10 are supplied to the character core matrix 6 as will be described in more detail hereinafter. The output of the character core matrix is provided asja parallel input to the deflection wavefonn generator 12 which utilizes the information supplied thereto from the character core matrix 6 to generate particular deflection waveforms characteristic of the character decoder. After this waveform generation in the deflection waveform generator, the deflection waveforms are supplied to a suitable display device 14 such as via the deflection plates or coils of a conventional cathode-ray tube.

In order to better understand the ensuing description of the system of the present invention, reference is now made to FIG. 2 which illustrates the actual technique utilized in forming the particular characters desired.

FIG. 2A shows an upper case letter "A." The short intersecting lines associated with this character divide V the character into a number of segments, in this case, nine segments. The segments are drawn so that at the end of one segment the next segment begins and that all the segments appear to be connected to form a set of continuous linear lines having different slopes. FIG. 2B and FIG. 2F show the horizontal waveform l6 and the vertical waveform 18, respectively, formed by the deflection waveform generator 12 previously referred to in connection with FIG. 1 These waveforms, when applied to the deflection system of a cathode-ray tube, will generate the character A as shown in FIG. 2A.

To obtain these waveforms the present invention utilizes the concept of integrating a specified number of pulses during a predetermined-uniform period of time to provide a series of linear waveforms of various slopes. To realize this, FIG. 2B illustrates a first group of pulses 20 at a particular frequency, for example f for a time duration equal to 6:. This period is subdivisible into six equal time increments equal to 1. Similarly, another group of pulses 22 of a polarity opposite those of pulses 20 are shown occuring during a time period equal to 7t--6t,, these pulses 22 being of a similar frequency as were pulses 20 previously referred to. Following these pulses 22, there occurs a third set of pulses 24 having a frequency different than f for example, a frequency f,. These pulses occur during the time interval equal to 91-7t, or during two equal increments of tine 1.

FIG. 2F shows the vertical waveform 18 which may be generated by integrating a first series of pulses 26 of a frequency f occurring for a duration equal to 3:, a second series of pulses 28 of an identical frequency but of an opposite polarity, and a third set of pulses 27 equal in duration to a period of time t and a frequency of f For the period of time between 7t and 9! no pulses occur since the vertical deflection waveform has a constant amplitude.

To further explain these waveforms l6 and 18, FIGS. 2C, D, and E show the particular pulses generally designated by reference numerals 21, 23 and 25, respectively, necessary in connection with the operation of the deflection waveform generator to permit the aforementioned pulse series of varying frequency to be integrated thereby forming the particular deflection waveforms described. Similarly, FIGS. 26, H, and I show the pulses, generally designated ny reference numerals 29, 31 and 33, respectively which permit the generation of the particular pulse trains of varying frequency previously alluded to. The broken vertical lines in some of the pulses of these FIGS. indicate the substantially simultaneous ending and beginning of two adjacent pulses. This has been shown in favor of a complete pulse.

Reference will now be made to the deflection waveform generator of FIG. 4 wherein certain conductors followed by the suffix "a are labeled with reference numerals identical to those used in FIGS. 2B-2I to designate particular pulses carried by these conductors.

Basically, the deflection waveform generator 12 includes six pulse sources or generators 30 each having its own unique frequency. As shown in FIG. 4, these frequencies have been designated 1",, f f3, f f and f,,. The output of each pulse source 30 is connected to a pulse shaper and splitter circuit 32 of conventional design to shape the pulses generated by pulse source 30 into rectangular pulses of both polarities. Those pulses having a positive polarity are provided at the output designated by the positive sign while those pulses having a negative polarity are provided at the output designated by the negative sign. Each of the outputs from a pulse shaper and splitter 32 is provided generally to the input of two AND

gates

34 and 36.

An exception to this are the pulse shaper and splitter circuits 32 associated with those pulse generators having the frequenciesf f and f,. In these cases, each output from the shaper and splitter circuit is provided to only one AND gate. The reasons for this exception will be seen in more detail as the description proceeds.

Still referring to FIG. 4 and the deflection waveform generator 12, the AND gates 34 have their outputs connected in common to the input to a conventional current integrator 38 which may be a capacitance circuit to produce an output voltage which is the integral of the input current applied thereto. Similarly, the output of AND gates 36 are connected in common to provide an input to integrator circuit 40 which may be of similar design as integrator 38. The outputs of these integrators are connected through

suitable amplifiers

42 and 44, respectively, to, for example, electromagnetic deflection coils 46 and 48 to control the horizontal and vertical displacement of the electron beam in the conventional cathode-ray tube 14. In terms of the Cartesian coordinates, x and y the pair of AND gates 34 whose outputs are connected in common and which are associated with each frequency source 30 influence the deflection of the electron beam either in the positive x direction or negative x direction depending upon its particular input from the pulse shaper and splitter circuit 32. Accordingly, the pair of AND gates 36 whose outputs are connected in common for each frequency source 30 control the deflection of the electron beam in the positive y or negative y direction also depending upon their input from the pulse shaper and splitter circuit 32.

As FIG. 4 shows, each of the AND

gates

34 and 36 have three inputs, one of which, as previously described, originates from the frequency pulse source 32. Another input is provided in the case of AND gates 34 from a flip-flop 50. In the case of AND gates 36, this second input is derived from flip-flop 52. The function of these flip-flops will be described in more detail hereinafter.

The third input to the AND

gates

34 and 36 originates from one of a plurality of pulse generating circuits 54 which have been designated r 2 t,, I, I r I, and 1, These pulse circuits may be of any conventional design such as a monostable multivibrator and function to produce upon a trigger signal at their inputs a pulse having a specified and equal time duration equal to t. The trigger signal which initiates the pulse from these pulse sources 54 is delivered to terminals 55 through 63, respectively, which correspond to identically designated output terminals from the character core matrix 6 shown more fully in FIG. 3. The outputs of these pulse sources 54 are connected to the gates identified by the subscript and the following .r" or y" designation. For example, the output of the pulse source designated I is applied to the input of AND gates 34 associated with the frequency pulse source 30 having a frequency f,.

In addition, the outputs of the pulse sources 54 having an x" designation are connected as inputs to a NOR gate 64 which provides a reset input to flip-flop 50. The outputs of the three pulse sources 54 having a y" designation are also connected as inputs to a NOR gate 66 which provides a reset input to flip-flop 52. The set input of these flip-

flops

50 and 52 are connected, respectively, to input

terminals

68 and 70 which also derive signals from the character core matrix 6. The purpose of these flip-

flops

50 and 52 is to control the application of the pulses of the proper polarity through AND

gates

34 and 36 depending upon the segment of the character to be generated. This will become more evident in connection with the description of the character core matrix of FIG. 3.

Reference is now made to FIG. 3 which shows in detail the character core matrix 6 previously referred to. This matrix comprises 14 columns of magnetic cores arrayed in l3 rows,

each column representing a segment in a character which can be generated in accordance with the principles of the present invention. Input signals are received from the character decoder 4 previously alluded to in connection with FIG. 1. The matrix then produces in parallel pulses at its output terminals which ultimately effect the deflection waveform supplied to the cathode-ray tube display device 14. As shown in FIG. 3, the character core matrix utilizes bistable magnetic cores 72 as the bistable elements, however, other suitable bistable elements may be employed as well. These magnetic cores are made of any suitable magnetic material having two opposed stable states of magnetic remanence which are designated the zero state and the one state in accordance with convention. Initially, all of the cores of the matrix are in a zero state which may be altered by the application ofa magnetizing field applied to any one of the cores by means of a set wire threaded through the core or combination thereof. When this positive magnetizing field is of sufficient intensity, the core is switched from the zero state to the one state. Subsequent application of a negative magnetizing field of sufficient intensity by means of a reset wire threaded through the core causes the core to be switched from the remanence condition representing the one state to the remanence condition representing the zero state. When the core switches from the one state to the zero state, an output pulse is generated on an output or read wire also threaded through the core.

For purposes of discussion and in the interest of clarity, only one set wire 74, for the character A," is illustrated. It should be realized however that there is one set wire for each character to be displayed and each of these set wires is connected to character decoder 4.

As shown, the set wire 74 for the character A actually consists of two electrically parallel set wires, one designated A and the other designated A These wires are threaded through particular cores in a manner to be explained hereinafter.

An output terminal representing each stage of the distributor or ring counter 10 is connected to one of the input terminals 76 which is coupled to the reset wire 78. These reset wires are conventionally threaded through every core in the column. The connection of these reset wires to the ring counter 10 is such so as to permit the sequential energization of the reset wires as the ring counter advances. For purposes of discussion, it may be assumed that the wires are energized in a sequence beginning from the left and going to the right of the FIG. is viewed. As the ring counter advances, negative magnetizing pulses are applied sequentially to the column reset wires of the character core matrix. These negative magnetizing pulses cause those cores in the one state in that particular column to return to the zero state. The cores which have not been set to the one state remain in the zero state upon application of the negative reset magnetizing field.

Through every core in a particular row, there is threaded a read wire 80 which is connected to an output terminal corresponding in reference numeral to an input terminal of the deflection waveform generator of FIG. 4. The energization of the reset wire for each column of the character core matrix generates the read pulses which will ultimately draw a particular line segment of a character on the screen of the cathoderay tube. As shown in FIG. 3, there are 14 columns in the matrix, thereby limiting the number of characters which can be drawn to those which require 14 or less segments. However, any number of characters may be synthesized within the 14 segments. Obviously, if it was desirable to synthesize character of more complexity than those using l4 segments, the number of columns in the core matrix could be increased to accommodate these more complex characters or symbols.

Referring now to FIGS. 2, 3, and 4, a typical operation of the circuit constructed in accordance with the principles of the present invention will be described in generating the character A." Assuming that the character decoder has identified the coded character stored in the storage register 2 and a particular set wire 74 is energized in the character core matrix. Those cores in the character core matrix which are threaded by this set wire are changed from their zero state to their one state.

At this point the ring counter commences its advancement, resetting the coresin the first column. This generates an output pulse at

terminals

56 and 63 which initiate a timed pulse of duration r at the output of pulse generators 54 designated t x and t y, respectively. These timed pulses are applied to the input of AND

gates

34 and 36, respectively, associated with frequency sources f and f With flip-

flops

50 and 52 in their initial reset condition, these AND

gates

34 and 36 are enabled to pass a specified number of pulses from their respective pulse shaper and splitter circuits 32 depending upon the frequency of the pulse source associated therewith. These pulses are applied to the current integrating

circuits

38 and 40 which integrate the succession of pulses into a substantially linear ramp signal which deflects the electron beam in the display device 14 accordingly.

The ring counter then advances one stage to reset the cores associated with the second column thereby generating two or more read or trigger pulses at

output terminals

56 and 63 respectively. As was the case previously described, these pulses initiate, in the example of the character "A," a similar number of pulses to be integrated by

current integrators

38 and 40 to deflect the beam again. This process is repeated until the character A has been completely traced on the screen of the cathode-ray tube.

As shown in FIG. 3, before grounding the A, branch of set wire 74, the set wire is threaded through a core associated with read wire 82'and output terminal 84. This core is in the same column as the last core threaded for this particular character. The read pulse generated when this core is reset to its zero conditionmay be utilized to reset the distributor 10 rather than have it continue through the remaining five columns.

Since some of the signals associated with the generation of the character A require negative pulses to be integrated to generate a negative x or negative y deflection, additional read wires 86 and 8d are provided to generate a signal at

output terminals

68 or 70, respectively, which indicates the times a pulse from one of the pulse generators 54 is to be applied to a gate associated with the negative output of the pulse shaper and splitter circuit 32. This decision is made by flip-flop or 52, depending upon whether it is a negative x or negative y signal. In either case, one of these flip-flops is set to provide a disabling signal to AND

gate

34 or 36 and an enabling signal to AND

gates

34 or 36 which permit negative pulses to pass to the integrating circuit during the generation of the timed pulse from generator 34. As the trailing edge of this timed pulse occurs, flip-

flop

50 or 52 is reset via the connection between the reset input of the flip-flop and NOR

gate

64 or 66.

Also, in the generation of particular characters, it is necessary and desirable to blank the beam of the cathode-ray tube during the deflection thereof over a particular segment of the character being synthesized. In order to accomplish this, an additional row of cores associated with read wire 90 are provided in the character core matrix and are associated with output terminal 92. This output terminal is connected to a suitable circuit 94 such as a monostable multivibrator of similar design as pulse generators 54. This circuit upon the receipt of a read pulse at output terminal 92 generates a pulse of sufficient amplitude and polarity to block the cathode-ray beam from striking the screen of the cathode-ray tube. The duration of this blocking signal is equal to the duration of the pulses generated by any one of the pulse generators 54. In this manner, any character or symbol may be generated and displayed.

As may be obvious from the above explanation, the interval between advancement in the distributor preferably is equal to the time r so as to permit the completion of each segment of the character before resetting the next column in the character core matrix.

It should also be noted that FIG. 2 is presented for purposes of illustration only and the waveforms included therein are shown in idealized form. The frequencies and pulse widths are not exact and are provided for their relative value at best.

Referring now to FIG. 5, there is shown in relative perspective actual character components or line segments utilized in accordance with the principles of the present invention to make up a particular font of characters which can be generated and displayed. Associated with each segment is the frequency at which this particular line slope and length may be generated with the selection of the proper time interval. The particular frequencies are a matter of choice depending upon the font desired and it is not necessary to specify the frequencies involved except to the extent that the subscripts indicate the relative frequencies they designate. For example, frequencyf is greater than the frequency j}, and less than the frequencyf Obviously, if one of the components or line segments illustrated in FIG. 5 may be in any desired quadrant of the Cartesian coordinates by selecting the proper polarity of the pulses to be integrated.

FIG. 6 shows three exemplary characters which may be generated using the line segments of FIG. 5 in the concepts of the present invention.

Upon the completion of the display of one character, it is necessary to position the beam to another initial point so that the next character may be displayed without interferring with the persistent display of the former adjacent character. This repositioning circuit is not necessarily described here since it is well known to provide conventional circuits in such electronic character generating systems. However, the pulse generated at output terminal 84 of the character core matrix of FIG. 4 previously alluded to for purposes of resetting the distributor or ringcounter 10 may be used to generate proper deflection voltages to cause the beam to be repositioned at a new initial reference position from which the next character may be initiated. This reference position may be the lower left-hand corner of the space allotted for the next successive character. Upon receipt or generation of this read pulse at output terminal 84, the beam could then be deflected to its new reference position.

While the invention has been described with reference to the circuit disclosed herein, it is not confined to the details set forth since it is apparent that certain electrical equivalent components may be substituted for the components of the preferred circuit without departing from the scope of the invention.

The invention is, therefore, to cover such modifications or changes as may come within the scope of the invention as defined by the following claims:

What I claim IS:

1. A character signal generating system for generating horizontal and vertical deflection signals which control an electron beam to trace any of a plurality of predetermined characters each of which is composed of segments having various slopes and lengths, said system comprising:

a. a horizontal integrator;

b. a vertical integrator;

c. a plurality of pulse generating means for generating a plurality of pulse trains each having a different frequency, each of said pulse generating means including a pulse train splitting circuit means for splitting each of said pulse trains into a pair of split pulse trains of like frequency to each other but of opposite polarity with each other;

(1. gating means for selectively gating in response to gate pulses any one of said split pulse trains to said integrators; and,

e. means for generating in response to a code signal representative of one of said predetermined characters any one of a plurality of predetermined sequences of gate pulses to said gating means.

2. A system as defined in claim 1 wherein said gate pulses having substantially the same pulse width.

3. A system for generating predetermined characters composed ofa plurality of successive straight line segments having various lengths and slopes in a display unit having signal integrating means for determining the slope and length of said segments comprising:

a. a first plurality of conductors for signals representative of deflections in one direction;

b. a second plurality of conductors for signals representative of deflections in another direction substantially perpendicular to said one direction;

c. means coupled to each of said conductors of said first and second pluralities for generating on selected ones of said conductors successive pulse trains during substantially uniform time intervals indicative of segments of a particular character to be displayed, at least one of said successive pulse trains having a pulse repetition frequency different from that of another one of said pulse trains; and,

d. means for coupling said first and second plurality of conductors to said signal integrating means.

4. A system as defined in claim 3 wherein at least one of said pulse trains has a polarity different from the polarity of another one of said pulse trains.

5. A character signal generating system for generating horizontal and vertical deflection signals which control an electron beam to trace any of a plurality of predetermined characters each of which is composed of segments having various slopes and lengths, said system comprising:

a. horizontal means having an input for generating a horizontal analog signal as a function of the number of pulses received thereby;

b. vertical means having an input for generating a vertical analog signal as a function of the number of pulses received thereby;

c. a first conductor coupled to the input of said horizontal means;

. a second conductor coupled to the input of said vertical means;

. a first plurality of gates, each having two inputs and an output, said output being coupled to said first conductor;

. a second plurality of gates, each having two inputs and an output said last recited output being coupled to said second conductor;

g. a plurality of pulse splitting means for generating two substantially identical output pulse trains of opposite polarity on first and second outputs, respectively, in response to an input pulse train at the input thereof, said output pulse trains having a frequency dependent on frequency of said input pulse train;

h. means for coupling said first output to the input of at least one of said gates in each of said pluralities of gates;

. means for coupling said second output to the input of at least one of said gates in each of said pluralities of said gates;

j. a plurality of pulse train generators each having an output coupled individually to one of said pulse splitting means and each having a different operational frequency; and,

k. means for selectively generating and applying any one of a plurality of predetermined sequences of gate pulses to the input of said gates of said first and second pluralities in accordance with one of said predetermined characters.

Claims

1. A character signal generating system for generating horizontal and vertical deflection signals which control an electron beam to trace any of a plurality of predetermined characters each of which is composed of segments having various slopes and lengths, said system comprising: a. a horizontal integrator; b. a vertical integrator; c. a plurality of pulse generating means for generating a plurality of pulse trains each having a different frequency, each of said pulse generating means including a pulse train splitting circuit means for splitting each of said pulse trains into a pair of split pulse trains of like frequency to each other but of opposite polarity with each other; d. gating means for selectively gating in response to gate pulses any one of said split pulse trains to said integrators; and, e. means for generating in response to a code signal representative of one of said predetermined characters any one of a plurality of predetermined sequences of gate pulses to said gating means.

3. A system for generating predetermined characters composed of a plurality of successive straight line segments having various lengths and slopes in a display unit having signal integrating means for determining the slope and length of said segments comprising: a. a first plurality of conductors for signals representative of deflections in one direction; b. a second plurality of conductors for signals representative of deflections in another direction substantially perpendicular to said one direction; c. means coupled to each of said conductors of said first and second pluralities for generating on selected ones of said conductors successive pulse trains during substantially uniform time intervals indicative of segments of a particular character to be displayed, at least one of said successive pulse trains having a pulse repetition frequency different from that of another one of said pulse trains; and, d. means for coupling said first and second plurality of conductors to said signal integrating means.

5. A character signal generating system for generating horizontal and vertical deflection signals which control an electron beam to trace any of a plurality of predetermined characters each of which is composed of segments having various slopes and lengths, said System comprising: a. horizontal means having an input for generating a horizontal analog signal as a function of the number of pulses received thereby; b. vertical means having an input for generating a vertical analog signal as a function of the number of pulses received thereby; c. a first conductor coupled to the input of said horizontal means; d. a second conductor coupled to the input of said vertical means; e. a first plurality of gates, each having two inputs and an output, said output being coupled to said first conductor; f. a second plurality of gates, each having two inputs and an output, said last recited output being coupled to said second conductor; g. a plurality of pulse splitting means for generating two substantially identical output pulse trains of opposite polarity on first and second outputs, respectively, in response to an input pulse train at the input thereof, said output pulse trains having a frequency dependent on frequency of said input pulse train; h. means for coupling said first output to the input of at least one of said gates in each of said pluralities of gates; i. means for coupling said second output to the input of at least one of said gates in each of said pluralities of said gates; j. a plurality of pulse train generators each having an output coupled individually to one of said pulse splitting means and each having a different operational frequency; and, k. means for selectively generating and applying any one of a plurality of predetermined sequences of gate pulses to the input of said gates of said first and second pluralities in accordance with one of said predetermined characters.