U.S. patent number 3,787,819 [Application Number 05/273,347] was granted by the patent office on 1974-01-22 for device for the processing of digital symbol data for the purpose of displaying text on a television monitor.
This patent grant is currently assigned to N.V. Hollandse Signaalapparaten. Invention is credited to Hendrik Busink.
United States Patent |
3,787,819 |
Busink |
January 22, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
DEVICE FOR THE PROCESSING OF DIGITAL SYMBOL DATA FOR THE PURPOSE OF
DISPLAYING TEXT ON A TELEVISION MONITOR
Abstract
A computer terminal for the processing of supplied symbol data
for the purpose of displaying lines of text on a television
monitor. The buffer memory of the computer terminal comprises an
input circuit and a plurality of cyclic submemories, where the
input circuit provides for the storage of the data required for
displaying one line of text in the respective submemory. The number
of times this data is fed from the respective submemory to a symbol
generator connected to the buffer memory, corresponds to the number
of scan lines required for displaying one line of text, the symbol
generator feeding the data of a desired scan line each time to said
monitor.
Inventors: |
Busink; Hendrik (Eibergen,
NL) |
Assignee: |
N.V. Hollandse Signaalapparaten
(Hengelo, NL)
|
Family
ID: |
19813677 |
Appl.
No.: |
05/273,347 |
Filed: |
July 19, 1972 |
Foreign Application Priority Data
|
|
|
|
|
Jul 23, 1971 [NL] |
|
|
7110158 |
|
Current U.S.
Class: |
348/600;
345/26 |
Current CPC
Class: |
G09G
1/00 (20130101); G09G 5/222 (20130101) |
Current International
Class: |
G09G
1/00 (20060101); G09G 5/22 (20060101); G06f
003/14 (); G08b 023/00 () |
Field of
Search: |
;340/172.5,324AD
;178/15,30 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Zache; Raulfe B.
Attorney, Agent or Firm: Trifari; Frank R.
Claims
1. A digital symbol diaplay device for the processing of symbol
data presented in digital form for the purpose of displaying text
on a television screen comprising a buffer memory, a symbol
generator connected to said buffer memory, and a timing unit
connected to said buffer memory and said symbol generator, said
device, in a first instance, presenting successive lines of text in
a read direction to the television screen, and, in a second
instance, replacing symbols randomly allocated and already
displayed by other symbols, said buffer memory being capable of
storing the maximum number of symbols to be displayed on the
television screen, said buffer memory being provided with a
plurality of cyclic submemories in each of which data required for
display and referring to one line of text can be stored in parallel
form, while the number of times at which said data is fed to said
symbol generator corresponds to the number of scan lines required
for the display of one line of text, the data required for display,
and pertaining to a desired scan line, each time being fed to said
television screen by the symbol generator, the buffer memory being
provided with an input circuit with each of said cyclic submemories
connected to said input circuit, the information required for
displaying one specific line of text being written into a
2. A device as claimed in claim 1, wherein the buffer memory
comprises a serial-parallel converter, which precedes and is
connected to the input circuit and via which the supplied serial
information is fed in parallel form to said input circuit, said
serial information being divided into symbol-type information, row
information and column information whereby the row information
indicates the cyclic submemory in which the symbol-type information
must be stored, while the column information is for the purpose of
determining the time at which the symbol-type information must be
stored at a fixed write-in location of said cyclic
3. A device as claimed in claim 2, wherein the input circuit
comprises a symbol register, a row register and a column condition
circuit connected to the timing unit, to which, respectively, the
symbol-type information, the row information and the column
information are fed, and whereby also a submemory selector is
present, which submemory selector is connected to the column
condition circuit and the row register, and which delivers a
control signal at a time to be determined by the column condition
circuit, said control signal implementing the writing of said
symbol-type
4. A device as claimed in claim 3, wherein the column condition
circuit comprises a column register and a symbol counter, to which,
respectively, the column information and clock pulses derived from
the timing unit are fed, the column condition circuit also
containing an equivalence circuit which is connected to said column
register and said symbol counter, and which determines the moment
at which the submemory selector delivers said
5. A device as claimed in claim 4, wherein a gate circuit is
disposed in a return line of each cyclic submemory, the return line
being interrupted when the control signal is applied to said gate
circuit, during which the symbol information derived from the input
circuit can be written into said
6. A device as claimed in claim 1, wherein the buffer memory is
provided with a line selection circuit, via which the information
of one specific line of text to be displayed is fed from a
respective cyclic submemory to
7. A device as claimed in claim 6, wherein the line selection
circuit is composed of a counter, to which required count pulses
are applied by the timing unit, a decoder connected to said
counter, and a number of gate circuits connected to said decoder,
each of which is connected to one of the cyclic submemories,
whereby a signal corresponding to the decoded counter position
opens the gate circuit connected to an associated cyclic submemory,
enabling information to be transferred from the associated
8. A device as claimed in claim 1, wherein the information required
for displaying a line of text is stored in serial form in the
respective cyclic submemory and wherein the buffer memory is
provided with a line selection circuit, connected to said
submemories whereby the information of the specific line of text to
be displayed is fed, with the aid of the timing unit, from the
respective cyclic submemory, via said line selection
9. A device as claimed in claim 8, wherein, said device contains
means for employing the same shift frequency at the cyclic
submemories and at the serial-parallel converter and said device
being also provided with a switchable memory feeding a
recirculating memory for whose functioning two different
frequencies are available one frequency for storing the symbol
information, which is written in serial form in the cyclic
submemory, in the switchable memory capable to receive data in
parallel form, and the other frequency for transmitting data from
the switchable memory to the recirculating memory, the latter
frequency being equal to that of the symbol generator.
Description
The invention relates to a device for the processing of symbol data
presented in digital form for the purpose of displaying text on a
television monitor. The device consists of a buffer memory, a
symbol generator and a timing unit. The device can, on the one
hand, present successive lines of text in the read direction to the
television screen, and, on the other hand, replace symbols randomly
allocated and already displayed by other symbols. A buffer memory
is capable of storing the maximum number of symbols to be displayed
on the screen, and there is provided at least one recirculating
memory in which the data required for display, and referring to one
line of text, can be stored in parallel form, while the number of
times at which said data is fed to the symbol generator corresponds
to the number of scan lines required for the display of one line of
text. Each time the data required for display, and pertaining to a
desired scan line, is fed to said monitor by the symbol
generator.
The lines of text are made visible on the screen of the
above-mentioned television monitor by means of "horizontal line
scanning." Each line of text is formed by a fixed number of scan
lines. To obtain these scan lines, the electron beam in the picture
tube is deflected each time in the horizontal direction. With this
deflection, the electron beam strikes the screen at the positions
where the parts of the desired symbols pertaining to the respective
scan line must be displayed. Such a part of a line of text, to be
displayed in the horizontal direction is, owing to the rapidly
fluctuating grid voltage in the picture tube, built up of a series
of luminous points or luminous dashes, depending on the applied
fluctuating grid voltage. When the electron beam has completed a
horizontal scan, the beam performs a horizontal retrace on the
presence of a line synchronization signal required for this
purpose. The electron beam then starts a new horizontal scan, which
is somewhat lower than the previous one, because the beam is
deflected downward to some extent during each horizontal line scan.
If the beam has arrived at the bottom side of the screen, the beam
performs a vertical retrace on the presence of a conventional frame
synchronization signal, whereupon the beam can start anew with
horizontal line scanning. During such a retrace, a blanking signal
ensures that the electron beam is suppressed, preventing the
scanning of the picture screen. The above synchronization signals
and the blanking signals can be supplied, for example, by the
timing unit.
A symbol may already be recognized on the screen if it is
displayed, for example, on 10 scan lines, using only a part of each
scan line. The length of each of these parts of the scan lines is
such that, for example, seven luminous and equidistant dots or
dashes can be placed on each part. Hence, in this example, the
projection area of one single symbol will consist of a matrix of
ten by seven dots or dashes.
In addition to a space between two successive symbols pertaining to
one line of text, the length of this space being such that, for
example, four luminous dots or dashes can be placed on it, also a
line space is required between the lines of text. The latter space
may be obtained, for example, by leaving blank three scan lines
preceding, and five scan lines following a line of text. Thus the
picture screen field may be divided into matrices of eighteen by
eleven dots, each of which allows the placing of one symbol only.
In this way, when using a television monitor suitable for a
C.C.I.R. 625-line standard signal, 32 lines of text can be
displayed on the screen and 49 scan lines will still be left over.
These scan lines are not used, however, because the time needed for
making use of this is required to perform two vertical retraces,
provided the generally applied principle of interlaced scanning is
used; first the odd-numbered scan lines are traced sequentially and
then, after a vertical retrace, the even numbered scan lines. The
consecutively projected "frames" thus obtained, together form the
desired display. For the sake of clarity of the description, the
principle of interlaced scanning on the monitor will be deviated
from, if necessary.
A device, as described in the opening paragraph is shown in the
Dutch Patent application No. 6817586. In the device of this patent
application the buffer memory comprises a closed magnetostrictive
delay line, a shift register and a recirculating memory. The
information relative to the total text to be displayed on the
television screen and derived, for example, from a computer, is
inserted serially into the above-mentioned delay line, and then
cyclically shifted in this delay line. The part of this information
which is required for displaying one single line of text, is
presented each time to the shift register. This information is then
read out per symbol in parallel form from the above shift register,
and fed to the recirculating memory.
If at a certain moment, a symbol already displayed is to be
replaced by another symbol, the corresponding symbol information in
the buffer memory must be replaced by new information to this
effect; this can be done only at the fixed write-in location of
this buffer memory. Since the symbol information to be changed may
be found at a random location in the buffer memory at the given
moment, such information cannot be replaced directly. If a delay
line, as described in the above-mentioned Dutch Patent Application,
is employed, a relatively long waiting time must usually be taken
into account before the symbol information can be changed at the
fixed write-in location. This is because the symbol information
must usually pass through half of the number of the available
memory locations, before the write-in location has been reached.
Since the time required by the symbol information to be shifted
cyclically once in the delay line must be equal to the frame time,
i.e. the time required to form an interlaced frame on the screen,
the mean waiting time will be equal to half of the frame time. With
the conventional frame frequency of 50 Hz, this mean waiting time
is 10 msec, which implies that the communication line between
computer and buffer memory is occupied a relatively long
period.
In order to process in the buffer memory the presented symbol data
in a simple and relatively rapid way, it is desirable to shorten
the mean waiting time before symbol data can be stored.
Hence, the object of the invention is to provide a device, of the
kind set forth in the opening paragraph, that fully meets this
desire. In accordance with the invention, the buffer memory used in
said device is provided with an input circuit and a plurality of
cyclic submemories. The information required for displaying one
specific line of text is written into the respective submemory with
the aid of the input circuit.
If it is desired to replace symbol information in the buffer memory
by other information, a waiting time is to be observed during which
this information is shifted cyclically to the write-in location of
the respective submemory; this usually takes a time that
corresponds to the period during which the symbol information
passes through half of the number of the available memory locations
of the respective submemory.
In a first version of the device in accordance with the invention,
one of the cyclic submemories is formed by said recirculating
memory, while the remaining submemories are identical to this. The
time, during which the information is shifted cyclically once in
the recirculating memory, is equal to the time during which one
scan line can be generated (scan line time). Consequently, the mean
waiting time preceding the moment of storing new symbol information
is equal to half of the scan line time. Taking into account the
interlaced display, at which only half of the number of scan lines
is displayed during the frame time, the scan line time will be 1/50
.sup.. 2/625 sec = 64 .mu.sec with the use of 625 scan lines for
displaying text on a television screen, and therefore the mean
waiting time for storing new symbol information will take 32
.mu.sec.
In a second version of the device in accordance with the invention,
the symbol information of each line of text is written serially
into the respective cyclic submemory. With the use of a specific
shift register, this stored symbol information is extracted from
the respective submemory per line of text, and presented in
parallel form to the recirculating memory. The symbol information
stored in the submemory must have been shifted cyclically once in
the same time during which a line of text is being displayed on the
screen. If such a line of text including line space is realized by
making use of "2n" scan lines, the mean waiting time will be equal
to half of the time in which "n" scan lines will have been
generated; this waiting time is "n" times as large as that in the
first-mentioned version, and thus is "n".times. 32 .mu.sec, which
still is a reasonable reduction of the waiting time compared with
the mean waiting time in the cited Dutch Patent Application.
The invention will further be explained with reference to the
figures, of which:
FIG. 1 illustrates a block diagram of a first version of the device
in accordance with the invention;
FIG. 2 illustrates a more detailed block diagram of the buffer
memory incorporated in said device;
FIG. 3 illustrates a more detailed block diagram of a recirculating
memory;
FIG. 4 illustrates a block diagram of a second version of the
device in accordance with the invention;
FIG. 5A illustrates an example of a symbol to be displayed,
while
FIG. 5B illustrates the accompanying diagram of video signals.
In these figures like parts are designated by like reference
numerals.
FIG. 1 relates to a device for the processing of symbol data
represented in digital form for displaying text on a television
monitor, which device consists of a buffer memory 1, a symbol
generator 2 and a timing unit 3.
The text to be displayed on the monitor may be composed of various
kinds of symbols; usually this is limited, however, to alphanumeric
symbols, viz, letters and numerals. In spite of this, other symbols
may appear in a text, such as mathematical designations, reference
marks, etc.
It is customary that the computer provides the symbol data; the
data is then presented in the form of code words. These code words
either refer to the type of symbol to be displayed, or to the
location on the monitor where a symbol should be displayed. The
length of the code words, in so far as they refer to the type of
symbol to be displayed, depends on the maximum number of symbols to
be used; if for the display a choice is made from 33 to 64 various
symbols, a code word should then comprise six binary digits. For
obtaining symbol data use may also be made of a keyboard, which is
then provided with an encoder. The code words, in so far as these
refer to the location where the symbols should be displayed on the
monitor, will either contain information of the line of text, or
information of the location on this line.
With the display of symbols on the screen in accordance with the
horizontal scanning described hereinbefore, it is important that
the information of the symbols to be displayed is available per
scan line. Depending on the scan line to be generated, and on the
symbol data presented, this information per scan line is supplied
by the symbol generator 2. To this effect, the number of successive
times at which the information referring to a line of text is
presented to the symbol generator 2, must be equal to the number of
scan lines used for displaying one single line of text including
line space. The signals (video signals) thus supplied serially by
the symbol generator 2 are fed to a combination circuit, which is
not indicated, and are hence converted, together with the
above-mentioned synchronisation and blanking signals, into a form
suitable for presentation to the television monitor in the
conventional manner. The latter signals provide the information of
the grid-cathode voltage to be formed. With the aid of this voltage
the luminous dots or dashes, comprising a part of the line of text
to be displayed in a horizontal direction, are obtained on the
screen.
In order to avoid continuous use of the computer for obtaining the
symbol data required for display, the device is provided with a
buffer memory 1 which precedes the symbol generator 2. The symbol
data presented by the computer is stored in this buffer memory; the
computer must be engaged only when the symbols displayed on the
television screen are changed, so that in the buffer memory 1, the
information corresponding to these symbols can be replaced by new
information. To this effect, a recirculating buffer memory 1 is
used, in which the symbol data passes through a certain cycle. At a
given moment during this cycle, the information of a symbol to be
displayed is extracted from the buffer register at a fixed location
in the buffer memory and fed to the symbol generator 2.
In accordance with the invention, the buffer memory 1 is provided
with a number of cyclic submemories 4a-z, connected in parallel,
which number corresponds to the maximum number of lines of text to
be displayed on the screen. Each submemory corresponds to a fixed
line of text on the monitor. In the version in question, each code
word, in so far as this refers to the type of symbol to be
displayed, is written in parallel form into a cyclic submemory.
Such a cyclic submemory should therefore contain a number of shift
registers operating in parallel, which number corresponds to the
number of binary digits, making up the written code word. The
combination of a number of shift registers operating in parallel
forms a recirculating memory. In the design in question, each of
the cyclic submemories 4a-z can therefore be regarded as one
recirculating memory.
In order that the symbol data, in so far as this refers to the type
of symbol to be displayed, is written into the desired
recirculating memory at the correct moment, the buffer memory 1 is
provided with an input circuit 5 preceding the recirculating
memories 4a-z. Since the respective symbol data is fed via a single
communication line from the computer to the buffer memory, and this
information is to be written in parallel form into one of the
recirculating memories, the buffer memory comprises a
serial-parallel converter 6 preceding the input circuit 5.
The sumbol data, once written in the recirculating memories 4a-z,
is read out symbol after symbol in order of succession of the
recirculating memories with the aid of a line selection switch 7
controlled by the timing unit 3, and said data is fed to the symbol
generator 2.
In the symbol generator 2, the symbol data is fed to a fixed matrix
memory 8. As will further be described hereinafter, also a signal
indicating a specific scan line is fed to this matrix memory with
the aid of a scan line switch 9. With these two kinds of data, the
matrix memory 8 is able to provide per scan line the information
referring to the symbols to be displayed, which information is
again supplied in parallel form to a parallel-serial converter 11
with the aid of the timing unit 3. The series of signals obtained
from the parallel-serial converter are fed as video signals to the
monitor.
FIG. 2 shows a more detailed block diagram of the buffer memory.
The function of the serial-parallel converter 6 contained in this
memory is, besides to convert serial data to parallel data, to
divide the supplied symbol data into: information referring to the
type of symbol to be displayed (symbol-type information);
information referring to the line of text in which the symbol must
be placed (row information) and information regarding the position
within this line of text on which the symbol should be displayed
(column information). The symbol-type information is written into
the symbol register 12. The row information is written into the row
register 13 and then fed to the submemory selector 14. The column
information is fed to the column condition circuit 15; this
comprises a column register 16, into which said column information
is written. Furthermore, the column condition circuit 15 comprises
a symbol counter 17, in which the clock pulses T.sub.2 derived from
the timing unit 3 are counted; these clock pulses have a repetition
time which is equal to the time required to display a scan line
part of one symbol on the television screen. The information of the
digital position of the symbol counter 17, and also the column
information stored in the column register 16, are applied
separately to an equivalence circuit 18 incorporated in the column
condition circuit 15; if the two kinds of information are
identical, the equivalence circuit 18 sends a signal to the
submemory selector 14.
In the version in question, the submemory selector 14 consists of a
decoder which is provided with a number of outputs A.sub.a-z. This
number corresponds to the number of recirculating memories 4a-z;
each of the outputs A.sub.a-z is connected separately to one of the
recirculating memories 4a-z.
The submemory selector 14 is activated by a signal originating from
the equivalence circuit 18 and, consequently, causes the
transmission of a control signal to the recirculating memory
corresponding to the respective row information via the appropriate
line A.sub.i (i = a, b, . . . , z). The working of these
recirculating memories 4a-z will now be explained by a further
description of the recirculating memory 4a, which is shown in FIG.
3. The recirculating memory 4a comprises, in addition to the
afore-mentioned number of parallel-connected shift registers 19 -
24, an equal number of return lines 25 - 30 and gate circuits 31 -
36. The working of the parts incorporated in the recirculating
memory 4a will be further explained with reference to the gate
circuit 31, the shift register 19 and the return line 25, which
elements are necessary, for example, for the processing of the
first binary digit of a code word from the symbol register 12. The
gate circuit 31 is a logical circuit of which the three inputs are
indicated by A.sub.a, f and g and the output by h. The control
signal from the submemory selector 14 is applied to the input
A.sub.a. It should be noted that this control signal is also fed to
the corresponding inputs of the gate circuits 32 - 36. The
information, which is obtained from the symbol register 12, and
which refers to the first binary digit of each code word, is
applied to input f, while the information from the shift register
19 is fed sequentially to input g via the return line 25. The
supplied information is fed to the shift register 19 via output h.
The latter information may be indicated by the relationship
h = A.sub.a .sup.. f + A.sub.a .sup.. g.
Therefore, in the presence of the control signal A.sub.a, the
information (f), which is derived from the symbol register (12,)
and which refers to said binary digit, is written into the
respective shift register 19 via the gate circuit 31. During this
process the information, which is fed from the shift register 19 to
the gate circuit 31 via the return line 25, will be eliminated. The
control signal A.sub.a is applied each time for the duration of the
writing of one binary digit. In the absence of the control signal
A.sub.a, the information (g) derived from the shift register 19 is
fed back to the shift register 19 via the return line 25 and the
gate circuit 31, and is rewritten in this register.
The remaining binary digits of these code words are fed to the
remaining gate circuits 32 - 36 in order to be written, after
selection, into the shift registers connected to said gate
circuits; the shift registers 19 - 24 operate with a shift
frequency which is equal to the pulse repetition frequency of the
clock pulses T.sub.2.
As shown in FIG. 2, the symbol-type information, once written in
the recirculating memories 4a-z, is extracted from said memories by
a line selection switch 7 and fed to the symbol generator 2. The
line selection switch 7 comprises a counter 37, a decocer 38, and
also a number of gate circuits 39a-z. The number of circuits 39a-z
corresponds to the number of recirculating memories 4a-z, so that
each gate circuit 31-36 can be connected to the symbol generator 2
via a separate gate circuit.
The counter 37 receives the clock pulses T.sub.4 from the timing
unit 3 with a repetition time which is equal to the time required
for displaying one complete line of text on the television screen.
The digital position of the counter 37 obtained through the clock
pulses T.sub.4 is decoded by the decoder 38. This causes the
activation of the gate circuit 39i (i = a, b, . . . , z) determined
by the count position via one of the outputs B.sub.a-z. The
information in the recirculating memory 4i connected to this gate
circuit can now be applied to the symbol generator 2. During the
period of time between two successive clock pulses T.sub.4, said
information is fed to the symbol generator 2 a number of times,
which number corresponds to the number of scan lines required for
displaying one line of text. For the processing of the symbol-type
information, the afore-mentioned matrix memory 8 is incorporated in
the symbol generator 2.
The scan line switch 9 in the symbol generator 2 comprises a line
counter and a line decoder connected to said counter, which are,
however, not shown separately in the figures.
Clock pulses T.sub.3 (see FIG. 2), of which the pulse repetition
period is equal to the time required for displaying a scan line on
the television screen and for performing a retrace, are supplied by
the timing unit 3 to the line counter of the scan line switch 9.
The count position acquired by said line counter is decoded by the
line decoder connected to the line counter; this information
enables the fixed matrix memory 8 to form, per scan line the
corresponding symbol information which, is then fed to the
parallel-serial converter 11.
Signals in serial form, viz., video signals, are obtained from the
parallel-serial converter 11 with the aid of the clock pulses
T.sub.1 provided by the timing unit 3. The pulse repetition
frequency of these clock pulses T.sub.1 is identical to the
frequency employed to obtain the rapid fluctuations in the
grid-cathode voltage of the picture tube for the formation of the
afore-mentioned luminous dots or dashes on the screen.
The operation of the above-described device will now be explained
with the aid of an example.
It will be considered how the device operates, for example, by
considering information relating to the letter "E" to be displayed
at the tenth position of the first line of text on the screen. The
computer will supply the serial-parallel converter 6, which is
illustrated in FIG. 2, with the row information, the column
information, and the symbol-type information required for
displaying the letter "E" in the form of the code words, for
example: (1,0,1,0,0,0,1), (1,0,1,1,0,0,1), and (1,0,1,0,0,0),
respectively. In this serial-parallel converter, the three supplied
code words are separated. The rwo information (1,0,1,0,0,0,1) is
written into the row register 13, and then fed to the submemory
selector 14. The column information (1,0,1,1,0,0,1) is written into
the column register 16, and then fed to the equivalence circuit 18.
Finally, the symbol-type information (1,0,1,0,0,0) is written into
the symbol register 12.
When the symbol counter 17 has acquired a binary count position,
which is identical to the column information (1,0,1,1,0,0,1), with
the aid of clock pulses T.sub.2, the equivalence circuit 18 sends a
signal to the submemory selector 14. Subsequently, in the submemory
selector 14, activated by said signal, the row information
(1,0,1,0,0,0) is decoded. This results in the example in question,
in which the first line of text must be displayed, in a control
signal at the output A.sub.a ; said control signal being applied to
the recirculating memory 4a. Although the information written in
the symbol register 12 is applied to all f-inputs of the gate
circuits in the recirculating memories 4a-z, this information is
accepted only by the gate circuits 31 - 36 activated by the control
signal, and written into the corresponding shift registers 19-24.
In this process, the first binary "1" of the symbol selection
information (1,0,1,0,0,0) is applied to the first shift register 19
via the respective gate circuit 31, and the second binary "0" to
the second shift register 20 via the respective gate circuit 32.
The remaining binary digits are then processed similarly in the
recirculating memory 4a.
When the digital position of the counter 37, which is illustrated
in FIG. 2, indicates that the first line of text must be displayed
on the screen, the decoder 38 activates the gate circuit 39a via
the line B.sub.a ; the information written in the recirculating
memory 4a is then fed to the symbol generator 2 via the gate
circuit 39a.
In addition to supplying the information written in the
recirculating memory 4a to the symbol generator 2, there is also a
supply of identical information to the gate circuits 31 - 36 of the
recirculating memory 4a via the return lines 25 - 30.
The information fed to the symbol generator 2 is accepted by the
fixed matrix memory 8. During the processing of symbol data by the
fixed matrix memory 8, an allowance must be made for a spaced
needed between two successive lines of text; this space is
obtained, on the one hand, by starting the symbol display, for
which the information is processed by the fixed matrix memory 8, at
the fourth scan line and, on the other hand, by adding another five
scan lines after the last scan line (13th scan line) pertaining to
such a display. Therefore, the letter "E" in this line of text is
given such a form that a horizontal line segment is displayed on
the 4th, 8th and 13th scan lines, at which the starting points of
these line segments are joined by a vertical line segment, as shown
in FIG. 5A.
With the aid of the information which is provided by the scan line
switch 9, and which refers to the scan line to be displayed, the
fixed matrix memory 8 is capable of delivering the information of
the line of text per scan line, and to feed this information to the
parallel-serial converter 11. With the delivery of information per
scan line, the space between two successive symbols must be taken
into account. Accordingly, the information provided by the fixed
matrix memory 8 with reference to the letter "E" for the fourth
scan line, may assume, for example, the form
(0,0,0,1,1,1,1,1,1,0,0); the number of binary digits comprised by
this information corresponds to the number of time intervals in
which the period of time for displaying one symbol is divided. If
the binary 1 is added to such a time interval, the electron beam
will strike the screen; if the binary digit is 0, the electron beam
will be suppressed during the respective time interval. If the
information of the line of text of the fourth scan line has been
fed to the parallel-serial converter 11, identical information will
again be sent to the fixed matrix memory 8 on the presence of a
line synchronization signal, after the latter information, returned
via the lines 25 - 30, has been restored in the recirculating
memory 4a.
Hence, the parallel-serial converter 11 provides the following
information per scan line for displaying the letter "E":
(0,0,0,0,0,0,0,0,0,0,0) for scan lines 1 - 3
(0,0,0,1,1,1,1,1,1,0,0) for scan line 4
(0,0,0,1,0,0,0,0,0,0,0) for scan lines 5 - 7
(0,0,0,1,1,1,1,1,0,0) for scan line 8
(0,0,0,1,0,0,0,0,0,0,0) for scan lines 9 - 12
(0,0,0,1,1,1,1,1,1,1,0) for scan line 13
(0,0,0,0,0,0,0,0,0,0,0) for scan lines 14 - 18
Since the binary 1 results in a positive grid pulse, the above
collection of information assigned per scan line corresponds with
the video signals shown in the diagram of FIG. 5B, which signals
are required for displaying the letter "E."
It must be emphasised that the complete data processing between the
serial-parallel converter 6 and the parallel-serial converter 11,
is carried out in parallel form. However, it is also possible to
process the symbol information in a serial form in the buffer
memory 1, whereupon this information is applied to the symbol
generator 2 in parallel form. A version of the invention based on
these lines will be explained with reference to FIG. 4. If parts of
the device in this version are not further dealth with, then an
analogous explanation, as given in the first version, will
apply.
The buffer memory 1 comprises a symbol separation circuit 48, an
input circuit 5, a plurality of cyclic submemories 4a-z, a line
selection switch 7, a serial-parallel converter 47, a switchable
memory 49 composed of a recirculating memory, and a recirculating
memory 50.
The symbol separation circuit 48 divides the supplied symbol
information into three kinds of information, viz,. the symbol-type
information, the column information and the row information, where
the column information and the row information are converted into
parallel form and so processed. These three kinds of information
are then fed to the input circuit 5, in which the symbol-type
information is written in serial form, while the row and column
information are processed into a control signal that must be
applied to the desired submemory 4i at the correct moment, in order
to write the symbol information stored in the input circuit 5.
The number of cyclic submemories is again equal to the number of
lines of text to be displayed; however, now each of the cyclic
submemories 4a-z is formed by a register, into which the symbol
information of one single line of text is written in serial form.
The symbol information written in each of the submemories 4a-z is
then fed sequentially to a serial-parallel converter 47 via a line
selection switch 7, and subsequently to the switchable memory 49.
Since the information is stored in serial form in the shift
registers 4a-z, and in parallel form in the switchable memory 49,
the shift frequency of the switchable memory 49 will be smaller
than that of the shift registers 4a-z by such a factor that
corresponds with the number of binary digits of which a code word
is composed. In order to operate the shift registers 4a-z and the
symbol generator 2 at the same frequency, the shift frequency of
the switchable memory 49 will, when this memory is provided with
information of a complete line of text, change in such a way that
this frequency corresponds to the operating frequency of the symbol
generator 2. The information of the switchable memory 49 is applied
with the latter frequency to a recirculating memory 50, which has a
constant shift frequency that is equal to the operating frequency
of the symbol generator 2. The number of times the information of
the recirculating memory 50 is fed to the symbol generator 2,
corresponds to the number of scan lines required for displaying one
line of text.
* * * * *