Stroke written shadow-mask multi-color CRT display system

A stroke writing generator develops selectively incremented and/or decremented horizontal and vertical deflection signals which simultaneously deflect all color associated beams of a conventional shadow-mask multi-color cathode ray tube to cause the beams to trace out a selected symbology on the tube screen. A video color code generator, operating in clock-defined synchronism with the stroke writing generator, selectively effects turn-on permutations of plural video amplifiers driving associated electron beams in the cathode ray tube to facilitate preprogrammed color tinting of the displayed symbology.

This invention relates generally to the display of graphics and symbology 
on a cathode ray tube screen, and more particularly to a means of 
generating and displaying selectively colored stroke-written symbology on 
a conventional shadow-mask multi-color cathode ray tube. 
The art of stroke writing on monochrome cathode ray tubes has been widely 
developed. State of the art stroke writing systems are digital in nature, 
and provide for displaying a selected imagery on a cathode ray tube by 
defining the imagery as a sequence of straight-line strokes of 
predetermined length and line slope. Horizontal and vertical deflection 
signals are developed as running digital counts in respective binary 
counters, with digital-to-analog conversion of these running binary counts 
providing analog deflection signals to control the deflection of the 
cathode ray tube beam in a manner that the selected character or imagery 
is written on the screen much in the manner of writing a symbology with a 
pen and a piece of paper. 
The advantages of stroke writing on a cathode ray tube reside in the 
inherently greater duty cycle with attendant increased beam on-time which 
is realized in writing the characters. It is known that, for a particular 
desired brightness of image display, stroke writing systems may employ 
appreciably lower cathode ray tube beam currents than those necessary to 
produce the same brightness of images on cathode ray tubes employing 
conventional raster scan displays. 
Thus prior art systems have clearly indicated and exploited the feasibility 
of stroke writing on monochrome cathode ray tubes. 
The obvious advantages of displaying symbology in the color domain are also 
well known in the art. In known raster scan/multi-color shadow-mask tube 
systems, symbology to be displayed is stored as digitized control signals 
for the colored cathode ray tube beams which are synchronized with the 
raster scan deflection circuitry employed. Such systems, while operating 
effectively to display symbology in a multi-color format, require 
extensive memory systems and complex interface synchronization with the 
raster scan deflection circuitries. Further as concerns raster scanned 
multi-color symbology display, the displayed symbols do not enjoy the 
sharpness and brightness of symbology written by stroke writing 
techniques. Further, such systems, in employing shadow-mask multi-color 
cathode ray tubes, suffer from the same disadvantage inherent in color 
cathode ray tubes, in that a large portion of the beam current impinges on 
the shadow-mask and high-beam currents are necessary to enjoy a 
high-brightness display. 
In addition to the known technique of raster-scan writing on shadow-mask 
multi-color CRT's , multi-color stroke written displays have employed a 
variety of techniques. Among such known techniques are the employment of 
cathode ray tubes utilizing penetration phosphors, current sensitive 
phosphors, refresh-sensitive phosphors, and the employment of band-pass 
filters with broadband phosphors. 
The penetration phosphor technique is based on the utilization of a 
phosphor whereby the color displayed is a function of cathode ray tube 
anode voltage. However, low anode voltage color in such systems is not as 
bright as high anode voltage color, resulting in a disadvantageous 
non-uniform brightness when displaying a variety of colors. Further the 
deflection gain employed in such systems must be adjusted as a function of 
anode voltage and, for high-speed color changes, the anode voltage power 
supply must switch the anode voltage in an extremely fast manner with 
attendant high power dissipation. In general, multi-color stroke written 
displays employing penetration phosphor cathode ray tubes suffer from high 
power dissipation, high cost, and display unit volumetric requirement 
greater than monochrome or shadow-mask color displays, and such techniques 
are limited currently to two colors, and mixtures thereof. 
In color stroke writing systems employing current sensitive phosphors, 
where color displayed is a function of cathode ray tube beam current, the 
low beam current colored data is extremely dim, and only two colors and 
mixtures thereof are presently available. 
In systems employing refresh sensitive phosphors, color is a function of 
refresh rate on a mixture of a short-decay phosphor with a long-decay 
phosphor. In such systems, however, the color associated with the 
long-decay phosphor is not adaptable to rapid data movement on the cathode 
ray tube screen, with the result that rapidly moving data displays are 
smeared. Additionally, such systems have a noticeable flicker of data 
drawn on the screen, due to the low refresh phosphor employed. 
In systems employing band-pass filters with broadband phosphors, display is 
limited to one color at a time and the systems are generally clumsy, 
cumbersome, and cannot be electronically controlled. 
Prior art techniques as to the display of symbology on cathode ray tubes 
has thus generally fallen into categories of monochrome raster; monochrome 
stroke writing; color raster; and color stroke writing employing 
techniques such as use of penetration, current sensitive and refresh 
sensitive phosphor tubes, as well as broadband phosphors with band-pass 
filters. In the known prior art, stroke writing has been associated with 
monochrome CRT's and with penetration, current sensitive, refresh 
sensitive and band-pass filter multi-color CRT's. Shadow-mask multi-color 
CRT's have been associated only with raster-scan display systems. 
The shadow-mask multi-color cathode ray tube, as widely employed in the 
television industry, has been a development of the television industry and 
employs a standard raster-scan display technique. As such, it has been 
assumed that a shadow-mask multi-color CRT tube, such as commonly employed 
in the television industry, must employ a raster scan beam deflection 
system in order to enjoy color definition. The assumption has been that a 
raster scan deflection system critically aligned with the geometry of the 
shadow-mask is a prerequisite for maintenance of color definition. As 
such, the known advantages of stroke written symbology on a cathode ray 
tube have not been enjoyed in the color domain. Those skilled in the art 
of stroke writing have assumed that multi-color shadow-mask cathode ray 
tubes may not be employed with stroke writing deflection systems, since, 
in stroke writing systems, the beam is caused to be deflected in numerous 
directions, and the only vector employed in a raster scan deflection 
system is that of successive lines written from left to right across the 
face of the tube, and in fixed geometrical alignment with the tube 
shadow-mask. 
I have found, however, that, although it has previously been considered 
that stroke writing techniques may not be employed with shadow-mask 
cathode ray tubes, shadow-mask multi-color cathode ray tubes may be stroke 
written without color loss or misalignment. This possibility was observed 
when the yoke of a raster-scan written shadow-mask cathode ray tube color 
display was rotated and the observed display showed no signs of color loss 
or misalignment, whereupon a stroke writing symbol generator and 
deflection system subsequently applied to a shadow-mask multi-color 
cathode ray tube resulted in an observed display which had all the 
characteristics of multi-color stroke written information with attended 
advantage of definition, brightness, and power saving. It is thus apparent 
that stroke writing in color on a multi-color shadow-mask cathode ray tube 
is possible, in that the beams of a shadow mask cathode ray tube are never 
totally hidden or blocked by the shadow-mask and that, additionally, the 
convergence system, once set up, is independent of the beam scanning 
method employed. 
Accordingly, the primary object of the present invention is to provide a 
stroke written shadow-mask multi-color cathode ray tube display system. 
A further object of the present invention is the provision of a system for 
displaying color-coded graphical and symbolic information employing stroke 
writing deflection techniques. 
Another object of the present invention is to provide an improved symbology 
display system operating in the color domain and providing improved 
display resolution, accuracy and definition over raster converted and 
scanned graphical displays. 
A still further object of the present invention is the provision of a 
symbology display system on a multi-color cathode ray tube which provides 
a wider range of color coded display information than is permissible in 
multi-color display systems utilizing voltage sensitive penetration 
phosphors, current density sensitive phosphors, or refresh rate and 
writing rate sensitive phosphors. 
Another object of the present invention is the provision of a multi-color 
symbology display system providing higher brightness and contrast than is 
possible with conventional raster scanned shadow-mask multi-color cathode 
ray tube displays or stroke written voltage sensitive penetration phosphor 
CRT displays. 
Another object of the present invention is the provision of a multi-color 
symbology display operating with less power consumption than known 
systems. 
The present invention is featured in the provision of a system employing a 
conventional shadow-mask multi-color cathode ray tube having respective 
red, blue, and green writing beam generation means each with an associated 
video amplifier. A stroke writing generator of conventional type is 
employed to effect predetermined horizontal and vertical deflection 
increments of the cathode ray tube beams, and means are employed operating 
in synchronism with the stroke writing generator to effect selected 
turn-on permutations of the associated red, green and blue video 
amplifiers during predefined deflection increment sequences, such that the 
displayed symbology may be selectively color coded.

With reference to the drawing, FIG. 1 shows a generalized system 
implementation of a stroke writing system employing a shadow-mask 
multi-color cathode ray tube. The system is basically comprised of a 
conventional stroke writing generator 10, which might comprise any number 
of known stroke writing generators known in the art, and, for the purposes 
of the present invention, may comprise a system such as described in my 
U.S. Pat. No. 3,775,760 entitled "Cathode Ray Tube Stroke Writing Using 
Digital Techniques", the teachings of which are incorporated herein by 
reference. The stroke writing generator described in my U.S. Pat. No. 
3,775,760, in common with other known stroke writing generators, responds 
to a digital input/output control line 11 to develop respective horizontal 
and vertical deflection signals 12 and 13 which are collectively 
definitive of cathode ray tube beam deflection to write a selected 
symbology as might be defined or commanded by the input/output line 11 to 
the stroke writing generator. Horizontal and vertical deflection signals 
12 and 13 are conventionally applied to associated horizontal and vertical 
deflection amplifiers 14 and 15 the outputs 16 and 17 of which are 
respectively applied to the horizontal and vertical deflection coils of a 
cathode ray tube to effect beam deflection such that the beam traces out a 
given symbology to be written on the face of the tube. As will be further 
described with respect to the monochrome stroke writing generator of my 
U.S. Pat. No. 3,775,760, the stroke writing generator, in addition to the 
horizontal and vertical deflection signal outputs, provides a video output 
control line 19 which is effective in controlling the video signal applied 
to the cathode ray tube 18 to selectively turn the beam on or off as may 
be required to realize the drawing of a particular symbology on the 
cathode ray tube. In accordance with the present invention, in addition to 
developing horizontal and vertical deflection signals to effect beam 
deflection to write a particular symbology, the stroke writing generator 
10 provides a color code output 20 which, as will be further described, 
defines the color of the information being written on the cathode ray 
tube. The color code output on line 20 may be controlled by data received 
over the input/output line 11 or by preprogrammed definitions in the 
stroke writing generator per se. The video control line 19 and color code 
control line 20 are applied to a video color coder 21 which develops 
respective control outputs on lines 22, 23 and 24 to effect turn-off and 
turn-on control of respective red, green and blue video amplifiers 25, 26 
and 27. The outputs 28, 29 and 30 from the respective color video 
amplifiers are applied in conventional manner to the shadow-mask 
multi-color cathode ray tube 18 for control of the red, green and blue 
electron beams generated by the tube. In general, the system depicted in 
FIG. 1 develops horizontal and vertical deflection signals which are 
linearly amplified and fed to the cathode ray tube deflection yoke. All 
three beams of the cathode ray tube are thereby deflected simultaneously 
and uniformly as described by the horizontal and vertical deflection 
signal outputs from the stroke writing generator. Video control and color 
control data are fed from the stroke writing generator 10 to the video 
color coder 21 which distributes the video information to the three video 
amplifiers in a manner presented by the color code signal to effect the 
color tinting of the symbology being displayed on the CRT. Preselected 
color tinting for a particular symbol to be stroke written, or for a 
particular portion of a symbol to be stroke written, as desired, may be 
encoded into storage means synchronously addressed by the stroke writing 
generator circuitry to control the red, green and blue video amplifiers 
driving the cathode ray tube color beams. 
The present invention, as generally embodied with the stroke writing 
generator of my above-referenced patent, is functionally depicted in FIG. 
2. Data to be displayed, as it appears on input output line 11, is 
transferred to a display data buffer 31. Buffer 31 addresses, through 
paralleled output lines 32, a display data decoder 34, and thus defines 
the graphics/symbology to be displayed. A clock 35 supplies a master 
timing input 36 to the display data decoder 34 to sequence the display 
data decoder in orderly fashion through routines necessary to generate the 
appropriate signals to fulfill the command from the display data buffer 
31. 
The display data decoder 34, which might comprise one or more read-only 
memories (ROMS), is depicted as generating seven discrete signals, 
identified as: 
1. Deflect beam left. 
2. Deflect beam right. 
3. Deflect beam up. 
4. Deflect beam down. 
5. Vertical clock rate. 
6. Horizontal clock rate. 
7. Video (write/blank on CRT). 
The first six signals of the above discrete list are generally utilized to 
command vertical and horizontal up/down counters depicted as X-UP/Down 
counter 37 and Y-Up/Down counter 38. The outputs 39 and 40 from the 
respective counters are processed by respective digital to analog 
converters 41 and 42, depicted as X-DAC and Y-DAC respectively. The 
digital-to-analog converters 41 and 42 convert the moving digital 
deflection codes as applied from the respective counters to 
incremented/decremented analog X and Y beam deflection signals. The video 
signal 19 from the display data decoder 34 commands the write/blank 
circuits of the multi-color shadow-mask cathode ray tube 18 synchronously 
with the X and Y deflection signals. As described in detail in my 
above-referenced patent, the X-clock and Y-clock outputs, 36a and 36b, are 
depicted in FIG. 2 as applied clock inputs to the respective X and Y 
up/down counters, and determine the relative rates at which the counts in 
the respective counters increase or decrease during the time duration of 
left-right and up/down commands applied, and thus collectively may define 
the slope of a straight-line segment which may be traced on the cathode 
ray tube. 
Outputs 12 and 13 from the respective digital-to-analog converters 41 and 
42 are shown in FIG. 2 as being applied to associated deflection 
amplifiers 14 and 15 which develop respective X and Y deflection signals 
16 and 17 for application to the horizontal and vertical deflection coils 
of the cathode ray tube 18. 
As will be further described, and, as depicted generally in FIG. 2, the 
command output 32 from the display data buffer 31, which is effective in 
development of X and Y deflection voltages to write a selected symbology, 
is additionally applied as input to video color coder 21. The video 
blank/write output 19 from the display date decoder 34 is also applied to 
video color coder 21. Color defining code outputs on lines 22, 23 and 24 
from the video color coder 21 are applied to respective red, green and 
blue video amplifiers 25, 26 and 27, outputs 28, 29 and 30 of which are 
applied to the cathode ray tube 18 to control turn-on of the respective 
red, green and blue beams in the shadow-mask multi-color CRT 18. 
In general then, FIG. 2 depicts the development of horizontal and vertical 
deflection signals commanded in such a fashion as to cause the three beams 
in CRT 18 to be simultaneously deflected to effect the writing of a 
particular symbology as commanded by input data on line 11. The buffer 31 
outputs a command signal 32 (for example, an address) which causes the 
display data decoder 34 to output a sequence of eight-bit words to effect 
the necessary video control and X and Y beam deflections to cause a 
particular symbology to be written on the CRT. The address or command 32 
from the display data buffer, in turn, is applied to the video color coder 
21 to synchronously develop video amplifier control signals in a selected 
permutation to define the color of the symbology being written. 
FIG. 3 illustrates the tie-in of the video color coder 21 and video 
amplifiers 25, 26 and 27 with a more detailed functional diagram of the 
stroke writing generator 10. A detailed description of the functioning of 
the stroke writing generator 10 will not be included herein, reference 
being made to my U.S. Pat. No. 3,775,760 for a detailed description 
thereof. For the purpose of the present invention, the stroke writing 
generator develops X and Y deflection signals to effect stroke writing of 
characters and provides a means of synchronously tying in a video color 
coder 21 to effect the writing of selectively colored symbology on 
multi-color shadow-mask cathode ray tube 18. 
As defined in my above-referenced patent, and functionally illustrated in 
FIG. 3, the stroke writing generator 10 provides for the display of 
sixty-four alphanumeric characters. A digital clock-controlled master 
timing system causes the beam to be positioned to predetermined successive 
start positions for each one of successive characters to be displayed. 
From each start position, the X and Y counters are commanded to cause the 
beam to follow a particular stroke sequence assigned to the character. The 
digital master timing system further effects necessary video blanking 
between characters, between the end of one line of characters and the 
beginning of a succeeding line of characters, and between the last 
character of the last line of the display and the repeat of the display 
sequence at the first character position of the first line of the display. 
Of significance to the present invention, is that the stroke writing 
generator 10 develops, on certain control lines, information which 
controls blanking of the video beam, and, in the instant invention, 
necessitates simultaneous blanking of all three of the color beams. The 
stroke writing generator of my previously referenced patent may thus be 
utilized essentially in its entirety, in conjunction with the video color 
coding arrangement herein described. 
The stroke writing generator depicted in FIG. 3 is a digitally controlled 
system for the display of sixty-four alphanumeric characters, each 
character defined by a maximum of twenty-four sequential beam stroke 
commands. Each of the twenty-four beam strokes is, in turn, defined by 
clock incremented or decremented counts carried in each of X and Y 
counters the outputs of which are converted to analog beam deflection 
signals. The stroke writing generator 10 employed in the embodiment of 
FIG. 3 includes a read-only memory means which may be addressed to supply 
the twenty-four stroke segments stored therein for the addressed one of 
sixty-four characters in the writing repertoire. X and Y counters are 
supplied inputs at a common system clock rate and caused to count up, 
count down or maintain status quo by .+-..DELTA.X and .+-..DELTA.Y input 
commands defined by the twenty-four stroke segments stored for a selected 
character. 
The stroke writing generator further comprises a master timing means 
comprised of digital dividers operated in cascade fashion under control of 
the master clock to provide X and Y beam start-position signals necessary 
to move the beam to a new starting point for each successive character to 
be written on a given line, and to cause the sequential characters to be 
conventionally displayed line by line. This portion of the stroke writing 
generator is significant to the instant invention only in that certain 
binary counts developed in the master timing generator generally depicted 
in the upper portion of FIG. 3 define periods when the video should be 
blanked, as during horizontal and vertical retrace intervals, etc. defined 
by the particular line and page format for which the stroke writing 
generator is designed. It is to be emphasized that no one particular kind 
of stroke writing generator is necessary as concerns the instant 
invention, since all stroke writing generators operate on the basis of 
some timing control, including, in most instances, requirement for video 
blanking. In the instant invention, blanking requirements must be utilized 
to shut off the three beams in the cathode ray tube for the same purpose 
as they would cut off the single beam in a monochrome display. 
FIG. 3 depicts a page format memory 43 as supplying an input 11 to a 
character buffer register 31. Character buffer register 31 represents an 
implementation of the display data buffer 31 depicted in the general 
system of FIG. 2. Page format memory 43 might comprise any one of a number 
of memory implementations by means of which a predetermined "page" to be 
displayed is stored, together with timing and control means to synchronize 
readout of the stored page of information with the character and line 
positions on the cathode ray tube display. Thus memory 43 might comprise 
an input keyboard along with a read-in and read-out control circuitry to 
control a line memory with associated input and output controls and a line 
memory clock control. The output 11 from the memory 43 may, for purposes 
of this description, be considered to be comprised of a source of 
sequential parallel six-bit character addressing words which are time 
synchronous with character and line positions of the display. Thus the 
output 11 from memory 43, for any given character to be displayed, would 
comprise six parallel binary bits which would be effective in addressing 
2.sup.6 or sixty-four different character words in the ensuing character 
memory portion of the display circuitry. The output 32 from character 
buffer register 31 would thus be comprised of a sequence of paralleled 
six-bit character address words related to the sequence of characters to 
be displayed, that is, a discrete six-bit address which is outputted on 
line 32 and uniquely present thereon during the writing of a character 
defined by that address. 
The display data decoder 34 of FIG. 2 is embodied in the system of FIG. 3 
as a read-only memory means which, in response to each six-bit character 
address present on character buffer register output line 32, initiates a 
sequential output of twenty-four character defining stroke words, each 
stroke of which is comprised of five bits (.+-.X deflection, .+-.Y 
deflection, and video on/off). The read-only memory means in FIG. 3 is 
embodied as three character defining ROM's 44, 45 and 46 which, under 
control of the master timing generator depicted in the upper portion of 
FIG. 3 and the particular character address present on the output 32 from 
character buffer register 31 collectively cause eight-bit segments of 
stroke defining command words to be sequenced through the ROM's 44, 45 and 
46. Outputs from each of the character defining ROM's are OR'd as a common 
input to a stroke buffer register 47, with the stroke buffer register 47 
providing the previously described +.DELTA.Y, -.DELTA.Y, +.DELTA.X, 
-.DELTA.X and video blank/write command words outputs which define the 
writing of the character. Outputs from the stroke buffer register are 
applied to the .DELTA.Y up/down counter 38 and .DELTA.X up/down counter 37 
in the form of commands which either increment, decrement or hold the 
existing count. The running counts held in the .DELTA.X and .DELTA.Y 
counters are applied through digital-to-analog converters 41 and 42 
outputs 12 and 13 of which are applied to respective .DELTA.X and .DELTA.Y 
deflection amplifiers 14 and 15 to supply analog deflection signals 16 and 
17 to the cathode ray tube deflection coils. 
Again it is to be emphasized that, for the purposes of the present 
invention, the particular read-only memory means and addressing technique 
employed in the system of FIG. 3 (as described in detail in my 
above-referenced patent) are not in and of themselves significant to the 
present invention. Of significance to the present invention is that the 
output 32 from character buffer register 31, in the form of an address 
uniquely definitive of a particular character being written at any 
particular time, provides a ready means for synchronizing and selecting a 
particular color which may be desired for that character. To this end, 
output 32 from character buffer register 31, in addition to being applied 
to the read-only memory means to effect the deflection signals for writing 
the character, is applied as an input to the video color coder 21, which, 
as will be further described, may provide means to effect a desired 
(programmed) video amplifier turn-on permutation for the duration of the 
writing of the character defined by the address on line 32. Note in FIG. 3 
that the video color coder 21 receives an additional input 19 (the 
write/blank command bit from the stroke writing buffer register 47). This 
bit will be utilized to turn off all beams in the cathode ray tube for 
certain retraced portions which may be defined in the writing of a given 
character. As described in my above referenced patent, these retrace 
portions (sequences where the beam is caused to deflect back over a 
portion of a symbol) would cause uneven character brightness were the beam 
not blanked during such retrace portions. Video color coder 21 in FIG. 3 
further receives an input 48 defined as "binary 13" which comprises an 
output from the master timing generator of FIG. 3 corresponding to 
vertical retrace time in the page writing format of the particular stroke 
writing generator employed. Video color coder 21 additionally includes an 
input 49 defined as "binary 16 and 17" which comprises a binary control 
waveform unique to the master timing generator of the system of FIG. 3 
during which horizontal retrace in the format is occurring, and during 
which period of time it is desired to blank the video. Again, as concerns 
the present invention, the particular unique video blanking inputs to the 
video color coder 21, as applied in the particular embodiment of FIG. 3, 
are not by way of limitation. It is noted that inputs 19, 48 and 49 to the 
video color coder each have in common a singular purpose, that of 
effecting a desired blanking of the cathode ray tube beams. A still 
further input 50 to the video color coder 21 of FIG. 3 comprises a 
particular binary level output from a delay flip-flop in the master timing 
chain of the system which input (as described in my above-referenced 
patent) is utilized to effect beam turnoff for a discrete interval of time 
during respositioning of the beam from the end writing position of one 
character to the start position of a succeeding character to be written. 
Thus input 50 to video color coder has, in common with other control 
inputs, that of commanded video beam turnoff in the system. 
The particular stroke writing generator implementation of FIG. 3, embodying 
that described in my above-referenced patent, developes beam positioning X 
and Y deflection signals for the start of characters to be written, as 
well as character writing X and Y deflection signals which are applied to 
separate respective pairs of deflection coils. For the purposes of the 
invention, this particular implementation is not limiting or necessary. 
For example, the outputs from the X and Y digital-to-analog converters 51 
and 52 of FIG. 3, as applied to X and Y amplifiers 53 and 54, might be 
applied as respective offset inputs to the .DELTA.X and .DELTA.Y 
deflection amplifiers 14 and 15 of FIG. 3. 
With reference to FIG. 4, a one-bit resolution video color coder 21 is 
embodied, whereby each of the red, green and blue video amplifiers 25, 26 
and 27 may be controlled on an on-off basis to effect color tinting of the 
written symbology. 
The video color coder 21 of FIG. 4 comprises a color coder ROM 60 which 
receives the six-bit character address from the character buffer register 
31 of FIG. 3. The six-line address on input 32 is thus capable of having 
developed thereon, for the particular sixty-four character repertoire 
capability of the described stroke writing generator, 2.sup.6 or 
sixty-four discretely different addresses. Color coder ROM 60 might be 
implemented as a 64.times.4 ROM having stored therein, at sixty-four 
discretely addressable positions, a four-bit color code word. For the 
purpose of the three video amplifiers herein being controlled, only three 
of these bits are used as they appear on output lines 61, 62 and 63, and 
may comprise a binary "1" on a particular line when it is desired to turn 
on a particular color video amplifier controlled by that line. Video 
amplifier turn-on/turn-off control is effected in FIG. 4 by the respective 
outputs 22, 23 and 24 from AND gates 64, 65 and 66 to which the output 
line 61, 62 and 63 from the color coder ROM are applied as respective 
first inputs. AND gates 64, 65 and 66, together with a NOR gate 67, 
comprise an enabling logic gating circuitry which, as previously briefly 
described, effects simultaneous blanking of all three cathode ray tube 
beams during particular intervals unique to the particular stroke writer 
employed. A second input to each of the AND gate 64, 65, 66 comprises the 
write/blank line 19 from stroke buffer register 47. Line 19 is false when 
the particular stroke writing command readouts call for video blanking, 
and it is seen that no logic "1" outputs may appear on lines 22, 23 and 24 
from associated AND gates 64, 65 and 66 should line 19 be false. 
Additionally, particular logic level inputs from the stroke writer 
embodied in FIG. 3 provide for a third input to each of the AND gates 64, 
65 and 66. Line 50 (the Q output from the delay flip-flop in the timing 
generator of FIG. 3), line 48 (corresponding to a vertical retrace time 
period in the page format of the stroke writer) and line 19 (corresponding 
to the horizontal retrace period of time unique to the stroke writer) are 
applied as respective inputs to NOR gate 67 the output 68 of which 
comprises a third input to each of the AND gates 64, 65 and 66. Inputs 50, 
48 and 49 to NOR gate 47, for the particular stroke writer embodiment 
herein described, are true when blanking of video is called for. Thus 
output line 68 from NOR gate 67 is false when blanking is called for. In 
the presence of a blanking (true) signal appearing on either of lines 50, 
48 or 49, line 68 is false and precludes development of true outputs on 
the video amplifier control output lines 22, 23 and 24. 
In operation, assume the address on input line 32 to the color coder ROM 
60, corresponding to a particular symbology to be drawn, selects a color 
code output word from color coder ROM 60 whereby line 61 is true and lines 
62 and 63 are false. In response to this color code output, AND gate 64 
developes a true output on line 22 to turn on the red video amplifier of 
FIG. 3, and the particular symbol being drawn will be displayed in red. 
Permutations of video amplifier turn-on are defined by different three-bit 
color code words as addressed from ROM 60. Thus the system of FIG. 4 
permits 2.sup.3 selective turn-on permutations of the three video 
amplifiers which control the beams of cathode ray tube 18, and the off-on 
control effected by the system of FIG. 4 permits a particular symbol being 
drawn to be displayed in green only, red only and blue only by turning on 
only that one of the three video amplifiers. In addition, all three video 
amplifiers may be commanded to be turned on and the symbol be written in 
white. A commanded turn-on of the green and the blue effects writing of 
the symbol in cyan and a turn on of the red and the blue video amplifiers 
effects a writing of the symbol in magenta. Thus, the simple one-bit video 
amplifier control (either on or off) afforded by the system of FIG. 4 
permits preselected writing of particular symbols in any one of seven 
colors, in addition, of course, to complete beam turnoff (black). 
While the range of color concerning written symbology made possible by the 
one-bit resolution system of the video color coder of FIG. 4 may be 
sufficient for a number of display applications, the video color coder may 
be expanded as desired to include multi-level turn-on of each of the red, 
green and blue video amplifiers. With reference to FIG. 5, a further 
embodiment of the video color coder 21 of the system of FIG. 3 is shown, 
wherein each video amplifier may be controlled by a two-bit command word, 
making possible the control of each video amplifier to the off state and a 
selected one of three levels of on-state. Tintings and shades of the 
colors made possible by the one-bit system of FIG. 4 may then be attained. 
With reference to FIG. 5, video color coder 21 is embodied in a manner 
similar to that of FIG. 4, with the color coder ROM 60' expanded so as to 
include two bits for each of the colors red, green and blue. Color coder 
ROM 60', as depicted in FIG. 5, might consist of a 64.times.8 ROM with two 
bits not used, leaving three pairs of output bits for respective control 
of the three video amplifiers. Color code ROM 60', in response to an input 
address on line 32 corresponding to a symbol to be drawn, outputs a 
selected eight-bit color code word. Bits 61a and 61b are applied as 
respective first inputs to a pair of AND gates 64a and 64b outputs of 
which are applied to a digital-to-analog converter to develop an output 
control for the red video amplifier which may command that the amplifier 
be off or operating at one of three commanded levels. The AND gate pair 
64a-64b receives blanking definitive inputs in a fashion similar to that 
of FIG. 4. Thus AND gate pair 64a-64b, in the absence of a system defined 
requirement for video blanking (as for retrace, etc.), develop outputs on 
respective lines 69 and 70 which collectively comprise two-bit words of 
00,01,10, or 11 depending upon the encoding of the addressed color code 
word in ROM 60'. AND gate outputs 69 and 70 are applied to a 
digital-to-analog converter 71 the output 22 of which is applied to the 
red video amplifier, and may be at a zero level or any one of three 
discrete levels to command that the red video amplifier either be off or 
generating a red beam at one of three levels. Similarly, output pair 
61a-62b from the color code ROM comprise respective first inputs to a 
further AND gate pair 65a-65b associated with the green video amplifier, 
and outputs 72 and 73 from this AND gate pair again, depending upon the 
word encoded in ROM 60' at the addressed location, collectively define a 
two-bit control word. Outputs 72 and 73 are applied to a digital-to-analog 
converter 74 the output 23 of which is employed to control the green video 
amplifier to either an off state or a commanded one of three "on" levels. 
Similarly, output bit pair 63a-63b from color code ROM 60' is applied as 
respective inputs to AND gate pair 66a-66b respective outputs 75 and 76 of 
which are applied to digital analog converter 77 to develop an output 24 
for control of the blue video amplifier to either the off state or a 
commanded one of three "on" levels. 
Obviously, the color code approach above-described with reference to FIGS. 
4 and 5 might be expanded as desired to effect a greater number of 
controlled levels of the three color video amplifiers towards approaching 
a full spectrum control of color as concerns the symbology being stroke 
written. 
The present invention provides a stroke written shadow-mask multi-color 
cathode ray tube display system. The system herein described embodies a 
conventional stroke writing generator (embodied as that described in my 
U.S. Pat. No. 3,775,760), conventional linear deflection amplifiers, 
conventional red, green and blue video amplifiers, a conventional 
shadow-mask multi-color cathode ray tube as widely employed in the 
television industry, a conventional deflection yoke, and a video color 
coder. The stroke writing generator receives graphical and/or symbolic 
data over input/output lines. This data is processed into conventional 
stroke written deflection and video signals. In addition, a color code is 
generated which defines the color of information being written on the 
cathode ray tube and is synchronously controlled in conjunction with the 
stroke writing process by either or both data received over the 
input/output line or preprogram definitions in the stroke writing 
generator. All three beams of the cathode ray tube are deflected 
simultaneously by the X and Y deflection signals developed by the stroke 
writer, with video and color code data being fed from the stroke writing 
generator to the video color coder. The video color coder distributes the 
video information to the three video amplifiers associated with the color 
cathode ray tube in a manner commanded by the color code signal to effect 
the color tinting of the stroke written symbology. 
The particular embodiment herein described utilizes the particular stroke 
writing generator defined in my above-referenced patent, wherein an 
address is present in the stroke writer which is uniquely associated with 
a particular character being written, and the embodiment of the color 
stroke writing system utilizes this address to effect a particular tint of 
the character defined by that address. It is to be realized that various 
other color control arrangements might be employed. For example the stroke 
writer might comprise a symbol generating device capable of drawing lines, 
circles, tracing out a labeled map display, etc. The teachings of the 
present invention extend to any type of stroke writing generator by 
scynchronous tie-in with a video color coder, such that selected symbols 
or portions of symbols in any desired form may be tinted in accordance 
with a pre-defined color. 
Thus, although the present invention has been described with respect to a 
particular embodiment thereof, it is not to be so limited, as changes 
might be made therein which fall within the scope of the present invention 
as defined in the appended claims.