U.S. patent number 3,696,388 [Application Number 05/099,342] was granted by the patent office on 1972-10-03 for apparatus for generating characters.
Invention is credited to William E. Eichelberger.
United States Patent |
3,696,388 |
Eichelberger |
October 3, 1972 |
**Please see images for:
( Certificate of Correction ) ** |
APPARATUS FOR GENERATING CHARACTERS
Abstract
Characters are displayed on the screen of a cathode ray tube.
The cathode ray tube electron beam is deflected in a trace
representing the character to be displayed by sequentially applying
various waveforms to the cathode ray tube deflection circuit.
Digital control circuitry including a read only memory having
segment deflection commands for each character to be displayed,
shift registers set by the deflection commands, and AND gates
enabled by the shift registers control the sequential application
of the various waveforms to the deflection circuit. An additional
shift register set by the deflection commands of the read only
memory, a single shot multivibrator, and an associated AND gate
control the intensity of the electron beam during the trace.
Inventors: |
Eichelberger; William E.
(Raleigh, NC) |
Family
ID: |
22274546 |
Appl.
No.: |
05/099,342 |
Filed: |
December 18, 1970 |
Current U.S.
Class: |
345/12; 345/27;
345/25 |
Current CPC
Class: |
G09G
1/12 (20130101) |
Current International
Class: |
G09G
1/06 (20060101); G09G 1/12 (20060101); G06f
003/14 () |
Field of
Search: |
;340/324A |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Trafton; David L.
Claims
What is claimed:
1. A character generator system comprising:
a display device including a screen means and an electron beam
generating means;
a beam deflection means for deflecting said electron beam through
position-to-position segments of a character trace;
a plurality of waveform generators producing a plurality of
different waveforms for use by said beam deflection means in
deflecting said electron beam through said position-to-position
segments of a character trace;
a deflection memory means for storing position-to-position segment
deflection commands representing the sequential and selective
application of said different waveforms to said beam deflection
means for each of the characters to be displayed, said memory means
selectively reading out said segment deflection commands for the
particular character to be displayed; and
a digital deflection control means including a plurality of
deflection register means associated respectively with said
plurality of waveform generators, said plurality of deflection
register means being coupled to said memory means so as to store
said segment deflection commands for said particular character to
be displayed, each of said register means storing a plurality of
said segment deflection commands representing the sequential and
selective application of the waveform produced by said associated
waveform generator for said particular character to be displayed,
said digital deflection control means controlling the application
of said waveforms to said beam deflection means in response to said
segment deflection commands stored in each of said deflection
register means.
2. The character generator system of claim 1 wherein each of said
deflection register means comprises a shift register having a
plurality of stages respectively set in response to said plurality
of segment deflection commands, said digital deflection control
means further comprising a plurality of deflection gate means
associated with and coupled to each of said shift register means
respectively, each said gate means being sequentially and
selectively enabled by the output of said associated shift register
means so as to sequentially and selectively apply the waveform
produced by said associated waveform generator to said beam
deflection means in response to said plurality of segment
deflection commands.
3. The character generator system of claim 1 further
comprising:
an intensity memory means for storing position-to-position segment
intensity control commands representing the sequential and
selective application of an intensity control signal to said
electron beam generating means for each of the characters to be
displayed, said intensity memory means selectively reading out said
segment intensity control commands for the particular character to
be displayed; and
digital intensity control means including an intensity register
means coupled to said intensity memory means so as to store a
plurality of said segment intensity control commands for the
particular character to be displayed, said digital intensity
control means generating an intensity control signal corresponding
to said segment intensity control commands stored in said intensity
register means.
4. The character generator system of claim 3 wherein said intensity
register means comprises a shift register having a plurality of
stages set in response to said segment intensity control commands
stored in said intensity memory means, said digital intensity
control means further comprising gate means sequentially and
selectively enabled by the output of said intensity shift register,
said intensity control signal being generated at the output of said
intensity gate means.
5. The character generator system of claim 4 wherein said digital
intensity control means further comprises a single shot
multivibrator circuit having an input coupled to at least one of
said deflection shift register means and an output coupled to said
intensity gate means so as to momentarily decrease the beam
intensity at the onset of a pulse from the output of said at least
one said deflection shift register.
6. The character generator system of claim 1 wherein said different
waveforms generated by said waveform generator include sinusoidal
waveforms and D.C. waveforms, said deflection registers associated
with said waveform generators producing said D.C. waveforms having
an output coupled to said intensity gate means.
7. The character generator system of claim 1 wherein said
deflection memory means is a read only memory comprising diode
matrices connecting two sets of lines, one set of said lines
corresponding to different characters and the other set of said
lines corresponding to the position-to-position segment deflection
commands.
Description
BACKGROUND OF THE INVENTION
This invention relates to character generators.
In one type of prior art character generator known as a dot matrix
generator, predetermined patterns of dots in a dot matrix are used
to form the characters of a font. Columns and rows of dots are
sequentially addressed in order to activate the appropriate dots in
the predetermined pattern of each character. Since the sequential
addressing and relatively non-critical timing of the dot matrix
generator is convenient and economical from a design point of view,
this type of generator represents the most widely used technique
for alphanumeric character generation. However, the spaces between
the dots of the matrix result in characters having insufficient
shape detail for easy distinguishability from character to
character. The lack of distinguishability is particularly true for
lower case alphabetic characters.
Another type of prior art character generator is a stroke
generator. In a stroke generator, an electron beam is deflected in
response to an analog signal developed by combining sine and cosine
generators with electronic integrators. The resulting deflecting
forces on the electron beam, which are comparable to the sequential
addressing and digitally controlled dot-matrix generators, form
patterns on a screen by a method and a means similar to those
utilized in generating the well known Lissajous' patterns. The
characters produced by stroke generators are generally superior to
those produced by dot matrix generators as far as shape detail is
concerned since curves or small segment straight line
approximations of curves can be generated. However, the electronic
integrators which are utilized to develop an analog signal in the
stroke generators are prone to drift with a resulting variance in
particular characters with time. The electronic integrators are
also costly.
SUMMARY OF THE INVENTION
It is a general object of this invention to provide a generator for
characters having sufficient shape detail for easy character
distinguishability.
It is another object of this invention to provide a generator for
producing characters which do not vary with time.
It is a further object of this invention to provide a character
generator which is relatively economical.
In accordance with these and other objects, a character tracing
electron beam of a display device such as a cathode ray tube is
deflected from position-to-position of the display device screen by
sequentially applying various deflection waveforms to a beam
deflection means associated with the display device. The various
deflection waveforms are sequentially applied to the deflection
means under the control of a deflection control means including a
plurality of register means which selectively store
position-to-position segment deflection commands generated by a
read only memory for each character to be displayed screen. An
intensity control means which is also responsive to the segment
deflection commands may be provided for applying an intensity
control signal which is variable from position-to-position of the
character trace.
BRIEF DESCRIPTION OF THE DRAWINGS
For still further objects and advantages of the invention,
reference should be made to the following description taken in
conjunction with the accompanying drawings in which:
FIG. 1 is a schematic representation of a character displayed on a
generator display screen;
FIG. 2 is a block diagram of a character generator system embodying
the invention;
FIG. 3 illustrates the relationship of FIGS. 3a and 3b which are
schematic diagrams of the beam deflection circuitry in the system
of FIG. 2;
FIG. 4 is a schematic diagram of the beam intensity control
circuitry of the system of FIG. 2;
FIG. 5 illustrates waveforms generated by the circuitry of FIGS. 3
and 4;
FIGS. 6(a-g) illustrate individual waveforms utilized in generating
the composite waveforms of FIG. 5; and
FIG. 7 is a schematic representation of another character displayed
on the generator display screen.
DESCRIPTION OF A PREFERRED EMBODIMENT
FIG. 1 schematically illustrates a screen 20 of a display device
such as a cathode ray tube. The screen 20 which comprises a
continuum of material capable of emitting light energy under
electron bombardment is subdivided into a matrix of positions 1-15.
The electron beam generated by the display device is traced through
segments between a preassigned pattern of positions corresponding
to a particular character to be displayed. In the case of the
character B, the electron beam is traced through positions 1-6, 8,
10, 12, and 14 as shown.
A system for generating the position-to-position character trace
will now be discussed with reference to FIG. 2 wherein the screen
20 of FIG. 1 is the anode of a cathode ray tube 22. In order to
move the electron beam from position-to-position segments while
tracing out a character, deflection circuitry for both horizontal
or X axis and vertical or Y axis deflection is provided.
The segment deflection or positioning commands which control the
deflection from position-to-position for each character are stored
in read only memory means (ROM's) 24 (X & Y). Characters which
may be transmitted from a remote digital computer are decoded so as
to selectively enable one line at the input of each memory means 24
as will be described with reference to FIG. 3a. After the character
to be generated has been selected at the input to each memory means
24, the positioning commands for that particular character are
applied to X and Y axis digital deflection control means including
shift registers 26(X & Y), a source of gated clock pulses 28,
AND gates 30(X & Y), and waveform generators 32.
As will be described with reference to FIG. 3a and 3b, the
positioning commands are utilized to set the various flip-flop
stages of the shift registers 26. As the gated clock pulses are
applied to the input to the shift registers 26, the AND gates 30
are sequentially enabled so as to sequentially apply various
waveforms to the cathode ray tube deflection circuits 34(X &
Y).
In order to control the intensity of the electron beam during the
movement from position-to-position in the character trace, digital
intensity control circuitry is provided. As shown in FIG. 2, the
intensity control circuitry also includes a read only memory 36
which provides intensity control commands corresponding to the
segments of particular character selected. The intensity commands
are then applied to a digital intensity control means comprising a
shift register 38, an AND gate 40, and a single shot multivibrator
circuit 42. The various stages of the register 38 are set by the
intensity control commands so as to sequentially enable the AND
gate 40 in response to pulses from the gated clock pulse source 28.
The output of the AND gate 40 is selectively enabled by the output
of the multivibrator circuit 42 in response to the output of the
shift registers 26(X & Y). An intensity amplifier circuit 44 is
coupled to the output of the AND gate 40 for appropriately
amplifying the intensity control signal before application to the
cathode ray tube 22.
The specific digital circuitry which may be utilized in achieving
the position-to-position X axis deflection of the electron beam
will now be discussed with reference to FIGS. 3a and 3b. It will be
appreciated that substantially identical circuitry is utilized for
Y axis deflection. As shown in FIG. 3a, the read only memory 24
comprises diode matrices 45(a-g) each having a plurality of input
lines A, B, C...for each of the alphanumeric characters to be
generated and a plurality of output lines 46(1-15), one output line
for each of the matrix positions. (For purposes of simplification
and clarity, only matrices 45a, b, & e have been shown.) When a
particular character is selected, i.e. a particular input line is
enabled, diodes 48 (a-g) associated with various output lines 46
become conductive in response to an input signal on one of the
input lines A, B, C . . . to set the corresponding flip-flop stages
50 of the shift registers 26(a-g). Simultaneously, an AND gate 52
is enabled by the input signal on the one input line so as to pass
a train of gated clock pulses from a source 54.
The output of each of the shift registers 26(a-g) sequentially and
selectively enables AND gates 30(a-g) associated with various
waveform generators 32(a-g) as shown in FIG. 3b. Depending upon the
character selected, one or more of the AND gates 30(a-g) may be
enabled by one or more of the shift registers 26(a-g) so as to
superimpose or sum various waveforms before application to an
amplifier 56 of the deflection circuit 34.
In order to achieve an appropriate composite waveform for
deflection in a horizontal or vertical direction, waveform
generators 32(a-g) generate the waveforms shown in FIGS. 6(a-g)
respectively. The various waveforms are set forth in the table
below:
FIG. 6a Sin (0.degree.-180.degree.) FIG. 6b Sin
(180.degree.-360.degree.) FIG. 6c Cos (0.degree.-180.degree.) FIG.
6d Cos (180.degree.-360.degree.) FIG. 6e D.C. one unit FIG. 6f D.C.
two units FIG. 6g D.C. four units
In order to provide a detailed description of the operation of the
digital circuitry of FIGS. 3a and 3b, the generation of the
character B as shown in FIG. 1 will now be described with reference
to the horizontal or X deflection composite waveform shown in FIG.
5. With the character B selected, the diodes 48a associated with
output lines 46-1, 2, 3, 4, 7, & 8 become conductive to set the
first, second, third, fourth, seventh, and eighth flip-flop stages
50 of the shift register 26a. Similarly, the diodes 48b become
conductive to set the fifth, sixth, ninth, and tenth flip-flop
stages of the shift register 26b and the diodes 48e become
conductive to set the third through tenth flip-flop stages of the
shift register 26e. Simultaneously, the gated clock pulses begin to
enter the shift registers 26 so as to sequentially enable the AND
gates 30a, 30b, and 30e.
As shown in FIG. 5, where the matrix positions are shown across the
top of the diagram and position 1 is the undeflected beam position,
the X deflection waveform begins at time t=0 when the AND gate 30a
is enabled by the output of the shift register 26a so as to apply a
sin (0.degree.-180.degree.) waveform from the waveform generator
32a to the deflection circuit 34. The AND gate 30a remains enabled
through time t=1 when the AND gate 30e is enabled. This
superimposes, or adds the DC one unit waveform of the generator 32e
to the sin (0.degree.-180.degree.) waveform of the generator
32a.
At times t=2-4 and 6-8, the AND gate 30a is again enabled. At time
t=4-6 and 8-10 the AND gate 30b is enabled to apply the sin
(180.degree.-360.degree.) waveform from the waveform generator 32b
to the deflection circuit 34. Throughout the time t=1-10, the
sinusoidal waveforms from the generators 32a and 32b are
superimposed on the DC one unit waveform from the generator 32e
since the AND gate 30e remains enabled throughout this period of
time. None of the AND gates 30(a-gare enabled from times
t=10-14.
Although the specific Y axis deflection circuitry is not shown in
FIGS. 3a and 3b, the circuitry would be identical except for the
coding of the diode matrices 45(a-g). In order to generate the Y
deflection waveform shown in FIG. 5, the Y deflection diode
matrices 45 of the memory 24(Y) would appropriately set the
flip-flop stages of the Y deflection shift registers 26c, d, e, f,
and g. From time t=2-4, the AND gates 30c and 30e would be enabled.
From time t=4-6, only the AND gate 30f would be enabled. From time
t=6-8, the AND gates 30c, e, and f would be enabled with the AND
gate 30g enabled from time t=8-10. From time t=10-12, the AND gates
30d, e, and f are enabled with the AND gates 30d and e being
enabled from time t=12 to t=14.
FIG. 5 also shows the intensity control waveform which is generated
by the intensity control circuitry shown in block diagram form in
FIG. 2 and in somewhat further detail in FIG. 4. The specific
circuitry comprises the memory 36 including a diode matrix 60
associated with the shift register 38. After a particular character
has been selected at the input to the diode matrix 60 the AND gate
40 is sequentially enabled so as to apply an appropriate intensity
control signal to the intensity amplifier circuit 44. When the
character B is to be generated with the intensity control signal of
FIG. 5, the first, third, fourth, fifth, seventh, eighth, ninth,
eleventh, twelfth, thirteenth, and fourteenth flip-flop stages of
the register 38 will be set by signals at the output lines of the
diode matrix 60.
The intensity control circuit as shown in FIG. 4 comprises the
single shot multivibrator circuit 42 which is stimulated by pulses
from either the X or Y shift registers 26e, 26f, and 26g. By
applying the output of the shift registers 26e, 26f, and 26g to an
OR gate 62, a single shot multivibrator 64 is stimulated by the
initial application of any DC waveform to the deflection circuits
34(X & Y). The multivibrator 64 which is normally in the high
state, drops to the low state for only a few microseconds
(deflection settling time) when stimulated by the OR gate 62
connected to the shift registers 26e, 26f, and 26g. When the
multivibrator 64 drops to the low state, the AND gate 40 drops to
the low state regardless of the output of the shift register 38. As
a result, the intensity control circuit cuts the electron beam of
the cathode ray tube 22 off, for a short period of time, while the
deflection is settling to a new DC level.
As shown in FIG. 5, the intensity control signal is in the low
state at times t=4, t=8, t=12 as a result of the multivibrator 64
operating in conjunction with the OR gate 62, the AND gate 40, and
the amplifier 44. These times represent the initial application or
onset of DC waveforms 6e, 6f, and 6g. Although times t=1, t=2, t=6,
and t=10 also represent the initial application of the DC
waveforms, the effect of the multivibrator 64 is masked since the
intensity control signal is in the low state in response to the
output of the shift register 38. The electron beam is therefore
essentially turned off at those points in time where a DC waveform
is initially applied so as to prevent displaying stray deflections
of the electron beam due to deflection waveform
discontinuities.
In order to more fully explain the manner in which a
position-to-position character trace is achieved, the trace of the
character B will now be described with reference to FIGS. 1, 5, and
6. In the following discussion, it will again be assumed that
position 1 of FIG. 1 represents the point of zero beam deflection
along both the X axis and the Y axis.
At time t=0, the sin (0.degree.-180.degree.) waveform of FIG. 6a is
applied for X deflection simultaneously with the DC waveform of an
intensity control signal at the upper level. During the period
between t=0 and t=1, the electron beam is traced between position 1
and position 6 as indicated in FIG. 5 and shown in FIG. 1.
At time t=1, the intensity control signal is reduced to the low
state to allow the sin (0.degree.-180.degree.) waveform of FIG. 6a
to complete its cycle. At time t=1, the one unit DC waveform of
FIG. 6e is also applied for X deflection. It appears from FIG. 1
that the electron beam remains at position 6 at time t=1 even
through a composite X deflection waveform has been applied which
does move the electron beam off position 6. Although the electron
beam does move from position 6, this movement is not seen on the
screen 20 since the intensity control signal is in the low
state.
At time t=2, the sin (0.degree.-180.degree.)waveform of FIG. 6a is
again superimposed upon or added to the one unit DC waveform of
FIG. 6e for X deflection and the cos (0.degree.-180.degree.)
waveform of FIG. 6c is superimposed upon the one unit DC waveform
of FIG. 6e for Y deflection. These waveforms continue through the
period of time t=2-4 with the intensity control signal being in the
high state. During this period, the trace moves from position 6
through position 12 and on to position 8.
At time t=4, the sin (180.degree.-360.degree.) waveform of FIG. 6b
is superimposed on the one unit DC waveform of FIG. 6e for X
deflection while the two unit DC waveform of FIG. 6f alone provides
the Y deflection as the electron beam moves from position 8 to 3.
The control signal drops to the low state momentarily at time t=4.
At time t=5, the control signal again drops to the low state to
allow the electron beam to retrace from positions 3 to 8 without
displaying the retrace on the screen of FIG. 1. The trace from
position 8 through position 14 down to position 10 is achieved by
again applying the sin (0.degree.-180.degree.) waveform of FIG. 6a
for X deflection superimposed upon the one unit DC waveform of FIG.
6e over the period t=6-8. Y deflection is achieved for this period
by superimposing the cos (0.degree.-180.degree.) waveform of FIG.
6c on the one unit and two unit DC waveforms of FIGS. 6e and
6f.
The trace from position 10 to position 5 is achieved between the
time t=8-9 by superimposing the sin (180.degree.-360.degree.)
waveform of FIG. 6b on the one unit DC waveform of 6e for X
deflection and utilizing the four unit DC waveform of FIG. 6g alone
for Y deflection. The intensity control signal drops to the low
state momentarily at time t=8. At time t=9, the intensity control
signal goes to the low state while the cycle of the sin
(0.degree.-180.degree.) waveform of FIG. 6b is completed. This
prevents the screen 20 from displaying any departure from position
5.
Finally, the trace of the character B is completed by moving the
electron beam from positions 5 through 4, 3, 2, and back to 1.
Since no X deflection is needed, the X deflection signal remains at
zero. In order to achieve the necessary Y deflection, the cos
(180.degree.-360.degree.) waveform of FIG. 6d is superimposed upon
the one unit plus two unit DC waveforms of FIGS. 6e and 6f for
times t=10-12. At time t=12, the cos (180.degree.-360.degree.)
waveform of FIG. 6d is superimposed upon the one unit DC waveform
of FIG. 6e. During the period from time t=10-12, the intensity
control signal remains in the high state except for a momentary
drop to the low state at time t=12.
The diode matrices 45 for X and Y deflection and the diode matrix
60 for intensity control are set forth below in chart form for both
the characters B and A. The lines a-g of the deflection charts
represent the shift registers 26(a-g) respectively and columns 1-15
represent the various stages of the shift registers 26(a-g). An "X"
indicates a diode connection between input lines B or A and lines
46(1-15) of the various shift registers 26(a-g). Similarly, the
single line in the intensity control charts represent the various
stages 1-15 of the shift register 38. An "X" indicates a diode
connection in the matrix 60 between a B or A input line and a stage
of the shift register 38.
X DEFLECTION FOR CHARACTER B
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 a X X X X X X b X X X X c d e X
X X X X X X X X f g
Y DEFLECTION FOR CHARACTER B
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 a b c X X X X d X X X X e X X X
X X X X X f X X X X X X g X X
INTENSITY CONTROL FOR CHARACTER B
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 X X X X X X X X X X X X X
DEFLECTION FOR CHARACTER A 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 a b
c X X d X X X X e X X X X X X f X X X g
Y DEFLECTION FOR CHARACTER A
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 a b c X X X X d X X X X e X X X
X X X X X f X X X X X X X X g
INTENSITY CONTROL FOR CHARACTER A
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 a X X X X X X X X X X
Appropriate diode matrices 48 and 60 for tracing other characters
on the matrix of FIG. 1 will be apparent in view of the foregoing
illustrations.
In order to generate certain characters including the character A
in classical form, it may be desirable to add additional diode
matrices, shift registers, AND gates, and waveform generators. For
example, the character A as formed on the position matrix of FIG. 7
includes a pair of inclined lines extending from positions 3 to 6
and 13 to 6. These inclined lines may not be formed with the
waveforms of FIGS. 6(a-g). In order to provide such inclined lines,
ramp generators may be utilized.
Even the character generator depicted in FIGS. 3a and 3b is
somewhat defficient with respect to the character B. In this
connection, it will be noted that the straight-line trace from
positions 1 to 6 was achieved by a sinusoidal waveform. By
utilizing the sinusoidal waveform, in particular the sin (0.degree.
- 90.degree.), the rate of trace decreased from position 1 to
position 6. In some instances, such an irregular rate of trace or
slewing rate may be noticable to the eye. It is therefore
preferable to utilize a ramp waveform providing a constant slewing
rate. In this connection, the frequencies of the sinusoidal
waveforms must be matched to one another and matched to the period
of any ramp waveform generators utilized.
In the embodiment described, there is no attempt to minimize the
logic circuitry. The logic circuitry required may be reduced by
providing further encoding and decoding combinations, especially in
the shift registers.
Although the invention has been described in terms of a particular
embodiment, various changes and modifications may be made without
departing from the spirit of the invention or the scope of the
appended claims.
* * * * *