U.S. patent number 3,603,966 [Application Number 04/799,265] was granted by the patent office on 1971-09-07 for data display system.
This patent grant is currently assigned to The Bunker-Ramo Corporation. Invention is credited to Roland S. Gregg, Jr., Herman F. Hoegeman, Jr..
United States Patent |
3,603,966 |
Gregg, Jr. , et al. |
September 7, 1971 |
DATA DISPLAY SYSTEM
Abstract
A CRT data display system is provided with means for entering a
character in memory for display in any position indicated by a
cursor signal. Once a character has been entered, the cursor is
automatically moved to the next character position in memory and
displayed. The cursor may also be moved without entering a
character. Character display is by a dot matrix such that n strokes
are required to display a character and an additional stroke is
required to provide an intercharacter space. The CRT beam is
blanked during the additional stroke. The cursor signal is stored
in a memory location read during the additional stroke period just
preceding the position into which a character may be entered.
Apparatus responds to the cursor signal a fraction of the time as
the displayed data is repeatedly read for CRT regeneration, thereby
displaying a blinking cursor. The cursor is displayed as a block in
the character position accessible for entry, all without
obliterating any character that may be present in that
position.
Inventors: |
Gregg, Jr.; Roland S. (Canoga
Park, CA), Hoegeman, Jr.; Herman F. (Thousand Oaks, CA) |
Assignee: |
The Bunker-Ramo Corporation
(Canogo Park, CA)
|
Family
ID: |
25175467 |
Appl.
No.: |
04/799,265 |
Filed: |
February 14, 1969 |
Current U.S.
Class: |
345/160;
345/16 |
Current CPC
Class: |
G06F
3/02 (20130101) |
Current International
Class: |
G06F
3/02 (20060101); G06f 003/14 () |
Field of
Search: |
;340/324.1 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Caldwell; John W.
Assistant Examiner: Trafton; David L.
Claims
We claim:
1. In combination with a display device including a movable writing
means actuatable to form a visible image on a target, control means
for controlling the movement of said writing means, said control
means comprising:
a cyclic memory containing a plurality of groups of bit storing
positions;
timing means for cyclically defining character sets of successive
time intervals, each character set being comprised of m intervals
with at least one of said m intervals serving as an intercharacter
space interval;
deflection means for causing said writing means to cyclically
describe a predetermined pattern on said target;
reading means for reading bits from a different one of said groups
during each of said intervals;
video means responsive to bits read by said reading means during
each of m intervals except for said intercharacter space interval
of each character set of intervals for selectively actuating said
writing means to describe a predetermined character on said target;
and
logic means responsive to bits read by said reading means during an
intercharacter space interval for causing said writing means to
display a cursor symbol at a predetermined location on said
target.
2. The combination of claim 1 wherein said deflection means causes
said writing means to describe a series of substantially parallel
strokes; and wherein
each of said groups read during said m intervals other than said
intercharacter space interval of each set of m intervals stores
video information with respect to a different one of said parallel
strokes.
3. The combination of claim 1 wherein said logic means responsive
to bits ready by said reading means during said intercharacter
space interval of a character set includes means for actuating said
writing means during predetermined intervals of the succeeding
character set.
4. In a data display system employing a CRT unit which displays a
plurality of characters, each in a dot matrix consisting of a
plurality of columns, each column having a series of dot positions
at which a beam of said CRT unit is unblanked in response to binary
digits of a video code serially read from a storage unit, and
wherein said CRT beam is automatically blanked for one complete
stroke between characters to provide a space between displayed
characters, said intercharacter blanking occurring while
intercharacter bit storage positions are read from said storage
unit to thus maintain synchronous operation between the movement of
said CRT beam and the reading of said storage unit, apparatus for
marking a given character position for selective entry of a new
character and for manifesting the accessibility of said given
character position comprising:
a cursor signal stored as a binary digit in one of said positions
of said storage unit read during an intercharacter stroke of said
CRT beam preceding a given character position;
means for detecting the presence of said cursor signal as said
intercharacter stroke bit storage positions are read;
marker means connected to said means for detecting a cursor signal
for causing said CRT unit to display a cursor symbol in the
character position succeeding said intercharacter stroke; and
entry means connected to said marker means for enabling new video
codes to be entered in place of the video codes stored in said
storage unit subsequent to said cursor signal.
5. In a data display system, apparatus as defined in claim 4
wherein said entry means includes means for advancing said cursor
signal from one of said positions of said storage unit read during
an intercharacter stroke of said CRT beam preceding said given
character position to a corresponding position of said storage unit
read during an intercharacter stroke of said CRT beam following
said given character position when a character is entered, thereby
automatically marking the next character position as accessible for
entry.
6. In a data display system, apparatus as defined in claim 5
wherein said entry means includes means for selectively advancing
said cursor signal to mark the next character position as
accessible for entry without entering a character.
7. In a data display system, apparatus as defined in claim 4
wherein said displayed characters are periodically refreshed at a
certain rate and wherein said cursor signal detecting means causes
said CRT unit to refresh said cursor symbol at a lesser rate
whereby said cursor symbol will appear as a blinking marker.
8. In a data display system, apparatus as defined in claim 7
wherein said entry means includes means for advancing said cursor
signal from one of said positions of said storage unit read during
an intercharacter stroke of said CRT beam preceding said given
character position to a corresponding position of said storage unit
read during an intercharacter stroke of said CRT beam following
said given character position when a character is entered, thereby
automatically marking the next character position as accessible for
entry.
9. In a data display system, apparatus as defined in claim 8
wherein said entry means includes means for selectively advancing
said cursor signal to mark the next character position as
accessible for entry without entering a character.
10. In a data display system of a type having storage means for
storing data to be displayed, each character of data being defined
by a predetermined video code, and the blank space between
characters being indicated by an intercharacter space code
consisting of at least one bit position of storage, and having
display means connected to said storage means for reading said data
for display, character by character, and for displaying said
characters with blank intercharacter spaces in response to the
video codes thereof regardless of the binary value of digits stored
in said intercharacter space codes between character defining video
codes, said display system further having entry means connected to
said storage means for entering video codes of new characters, one
character at a time on a selective basis, whereby an operator may
enter characters through a keyboard connected to said storage
means, apparatus for marking a given character position for
selective entry of a new character and for manifesting the
accessibility of said given character position comprising:
a cursor signal stored in said storage means as a binary code in
the intercharacter space code position preceding the video code of
said given character position;
means connected to said display means for detecting the presence of
a cursor signal between video character codes being read for
display; and
means connected to said cursor signal detecting means and said
storage means for displaying in said given character position a
manifestation marking it for entry of a new character code for
display
11. In a data display system, apparatus as defined in claim 10
wherein said display means reads said data for display cyclically
and displays each character during each cycle, and said cursor
signal detecting means is effective to display said manifestation
in said given character position once for every given number of
cycles, whereby said manifestation appears as a blinking
marker.
12. In a data display system, apparatus as defined in claim 11
including means connected to said display means for advancing said
cursor signal code from the intercharacter space preceding said
given character position to the intercharacter space following said
given character position for display of said blinking marker when a
character has been entered by said entry means, thereby marking the
next character position for entry of a new character code
therein.
13. In a data display system, apparatus as defined in claim 12
including means connected to said entry means for automatically
entering into said given position marked for entry a code
representing any character selected for entry by said operator
through said keyboard.
14. In a data display system, apparatus as defined in claim 13
wherein said display means comprises a CRT display unit and said
storage means comprises a cyclic display storage unit, whereby data
being displayed is cyclically read for refreshing the characters
displayed, each character being displayed by a succession of
strokes covering a character position during which a beam of said
CRT is unblanked by the video code of a character stored in said
storage means for display in that position and an additional stroke
before displaying a character in the next adjacent position during
which said beam is blanked and said intercharacter space code is
read to provide an intercharacter space, and wherein said cursor
signal detecting means includes means for producing a signal
enabling a character to be entered in the next character position
to be read upon detection of said intercharacter space code.
15. In a data display system, apparatus as defined in claim 14
wherein each character is displayed in a matrix of dots, each dot
being formed by unblanking said beam in response to binary digits
of said video code, and said cursor signal detecting means alters
the operation of said display means in all dot positions when it is
effective to produce said blinking marker.
16. In a data display system, apparatus as defined in claim 15
wherein said cursor signal detecting means alters the operation of
said display means by unblanking said beam at all dot positions,
whereby said blinking marker appears as a blinking block
superimposed on any character present in the position thus being
marked as accessible for entry.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to remote data display terminals and in
particular to display terminals having a character insertion
capability for editing.
2. Description of the Prior Art
Many remote data display terminals are being used in computer and
data storage systems as well as communication systems for composing
or editing messages, updating data, and the like. Cathode ray tube
(CRT) display units are ideally suited because of the fast rate at
which data may be displayed and altered. A typical unit may display
up to 15 lines of 64 characters. A display storage unit stores the
data in a recirculating memory so that it may be cyclically read
for regeneration of the characters on the face of the CRT. A
keyboard unit controls the display and enables the operator to
perform all data composition and manipulation tasks including
editing by selectively entering characters. A cursor of some form
is displayed to indicate to the operator the character position
available for entry through a file storage and control unit. The
keyboard unit is provided with control keys for positioning the
cursor.
Although the cursor may take various forms, such as a caret between
lines directly above or below the character position to be operated
on, the control unit will be more complex with such a cursor for it
must then effectively control the display of one additional line
just for the cursor. This is particularly true of display units of
the type in which each character is displayed as a 5.times.7 dot
matrix such that a line then consists of 384 strokes, six strokes
per character, each stroke only seven dots high. The strokes are
generated by a synchronized sawtooth wave generator connected to
the vertical beam deflection network and the dots are generated
through the beam blanking control network by a 7-bit code read from
the display storage unit for each of the first five character
strokes. During the sixth character stroke, the beam is blanked in
order to provide a blank space between characters.
In other systems, the cursor consists of a blinking line under the
character position on the CRT where the next operation will take
place. In still others, it consists of brackets around the
character position. Accordingly, some systems do not require an
additional display line, but all systems employing a recirculating
memory for display data storage have, in the past, required an
additional track or delay line just to store the cursor signal.
It would be desirable to store a cursor signal in the same delay
line or track of a recirculating memory employed to store the data
being displayed and to thereby mark the character position
accessible to the operator in such a manner that its display lies
within the same line as the character position being marked, but
without obscuring or masking any character present for display in
that position. Such a cursor signal should be easily advanced to
the next position, as when the operator makes an entry, without
interfering with any data being entered or in any way interfering
with a character being displayed in that position except by marking
it as the next character position to be acted upon.
SUMMARY OF THE INVENTION
The present invention is primarily directed to a CRT data display
system having a character insertion capability, and means
responsive to a cursor signal included with the data displayed for
marking a given character position for entry of a character from a
keyboard. In accordance with an embodiment of the invention, the
cursor signal is stored between character signals and read during
the intercharacter space display period just preceding the given
character position. The cursor symbol is displayed as a blinking
indicator, preferably a block, superimposed on any character that
may be present in the given position by having the cursor signal be
effective only a fraction of the cycles the character position so
marked is regenerated on the CRT screen. Entry of a new character
effectively erases any previous character and advances the cursor
signal to the next character position. Means for so advancing the
cursor signal without entering a character is also provided. For
purposes of this invention, a character is any letter, numeral,
punctuation mark, arbitrary symbol, or a blank character space, any
one of which may be selectively entered by actuating a key on the
keyboard unit.
In accordance with a preferred embodiment of the present invention,
each character is displayed in a 5.times.7 dot matrix. Each of the
five columns of the matrix constitutes one vertical stroke of the
CRT beam. Seven bit times are required for one stroke and one bit
time for return of the beam to the base of the line of characters
for the next stroke. Thus, video information is stored in a
recirculating memory in stroke groups, each group being comprised
of a certain number of bit storing position, herein eight. The
stroke groups are arranged m, herein six, to a character with a
certain number (m minus 1), herein five, being used to store video
information and with at least some (1), herein one, being used to
provide a space between characters on the display. The binary
digits are read from the memory in series and applied to a beam
blanking control system of the CRT during the first five stroke
intervals of a six stroke character set. The beam is blanked during
the entire sixth stroke interval to provide an intercharacter
space. A signal to generate a cursor for the next character
position is stored in memory in one of the bit positions
sequentially read during the sixth of intercharacter space stroke
time. That signal is not displayed as a dot because the beam is
blanked, but it is employed every so many cycles to display a dot
in all 35 dot positions of the next character without otherwise
disturbing any character displayed. Once a new character is entered
into the recirculating memory for display in the position marked by
the cursor, the cursor signal preceding that position in memory is
erased and a new cursor signal is stored in memory in a
corresponding bit position of the sixth (intercharacter space)
stroke of the character entered. If the operator elects not to
enter a character, he may advance the cursor signal from the
keyboard.
The novel features of the invention are set forth with
particularity in the appended claims. The invention will best be
understood from the following description when read in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a general block diagram of a CRT data display system of
the type for which the present invention is intended;
FIG. 2 illustrates an exemplary manner of producing characters on
the CRT of FIG. 1;
FIG. 3 is a block diagram illustrating an embodiment of the present
invention;
FIG. 4 is a block diagram illustrating an exemplary form of a data
control section of a control unit for the embodiment of FIG. 3;
and
FIG. 5 is a timing diagram for the operation of the embodiment of
FIG. 3 with the data entry control section of FIG. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to FIG. 1, a CRT display unit 10 is provided with a
cyclic display storage unit 11, such as a magnetic drum having a
plurality of tracks from which data to be displayed is cyclically
read for regeneration of characters on a CRT screen. A file storage
and control unit 12 provides bulk storage of data that may be
displayed and the necessary logic networks for controlling the
transfer of data to the display storage unit 11 and, in accordance
with the present invention, for editing data by the selective
insertion of characters in positions marked by a cursor displayed
as a blinking block consisting of 35 dots in a 5.times.7 matrix.
The transfer of data for display is controlled by an operator
through a keyboard unit 13. The keyboard is also adapted to give
the user maximum capability to arrange, manipulate, format,
inspect, and edit by inserting and removing data. The file storage
and control unit 12 is also adapted for use with external systems
through an optional interface represented by a bidirectional
transmission line 14.
FIG. 2 illustrates an exemplary manner for producing characters on
the CRT display unit 10 using a 5.times.7 dot matrix generated as
the beam sweeps through six strokes for each character under the
control of a sawtooth wave generator. As will be explained
hereinafter, the video code format of the data in the display
storage unit 11 is arranged in eight bit groups with each group
corresponding to a different beam stroke. Thus, during any given
stroke, the beam is turned on at each of seven points depending
upon whether a binary "1" for that point is stored in the
corresponding eight bit group in the display storage unit. For
example, to display the letter N, the video code would have a
binary "1" in each of seven bit positions of the eight bit group
corresponding to the first stroke. An eighth bit position is
provided in the code for each stroke but the beam is blanked during
that bit time regardless of the state thereof to allow the beam to
return to the base of the next stroke. As shown in FIG. 2, the
second stroke includes a binary "1" in the fifth bit position only.
Similarly, the video code group for the third and fourth strokes
include a binary "1" in the fourth and third bit positions,
respectively, while the video code for the fifth stroke is the same
as for the first stroke. During the sixth stroke, the beam is
blanked throughout all eight bit times to provide an intercharacter
space between the letter N and the subsequent character to be
displayed, shown as "A" in FIG. 2.
Since the CRT beam is blanked during the sixth stroke of each
character, the bit positions corresponding thereto in memory may be
used to store whatever nonvideo information is desired. Thus, in
accordance with the present invention, one of the bit positions
read during the sixth stroke is employed to store a cursor signal
so that, upon reading that signal, the storage and control unit 12
may cause the CRT unit 10 to display a cursor symbol, e.g., a dot
in each of the 35 positions of the next character. For example, if
a cursor signal is stored in the code group for the sixth stroke of
the video code for the letter N in FIG. 2, the file storage and
control unit 12 will cause a block of 35 dots to be superimposed on
the following character, i.e., the letter "A," thereby indicating
to the operator that a new character may be entered in that
position. The cursor signal is also used to time the storing of the
video code for the new character in the display storage unit.
In accordance with a further aspect of the invention, the file
storage and control unit 12 will respond to a cursor signal to
generate a block marker during only a fraction of the cycles that
the display storage unit 11 operates to regenerate the characters
on the CRT screen. In that manner, the cursor appears as a blinking
block superimposed on the character otherwise appearing in that
display position but allowing the operator to continue to view the
character upon which the cursor symbol is superimposed.
The operator may key any character he wishes to enter into the
position marked by the cursor symbol. The file storage and control
unit 12 then enters the video code of that new character in the
display storage unit 11 in place of the video code for the
character already being displayed the next time the display storage
unit 11 reaches that position for display regeneration, as
indicated by the cursor signal in the sixth stroke code group of
the character preceding it.
The file storage and control unit 12 not only enters the video code
for the new character but also automatically advances the cursor
signal from the sixth stroke code group of the preceding character
to the sixth stroke code group of the character being entered. The
operator may also advance the cursor signal from one character
position to the next by operating the appropriate key, or to any
other position by operating other keys.
It should be understood that the file storage and control unit 12
includes function control logic which sequences the data flow,
entry, and manipulation. Thus, when a function is specified by the
operator at the keyboard unit 13, a function code converter in the
unit 12 sends a service request to function control logic also in
the unit 12 in order that the appropriate sequence be
initiated.
The file storage portion of the unit 12 consists of a drum with a
plurality of tracks to be used as required not only to store data,
but also to manipulate data. In practice, the display storage unit
11 may also be implemented on the same drum. However, it should be
understood that the file storage may, for example, be comprised of
magnetic cores. The display storage unit 11 may also be of another
form, such as recirculating delay lines, or even a block of core
memory having work memory locations read cyclically, each word
having 48 bits for the six character strokes, or the equivalent.
The words would then be read from such a core memory in sequence
into a bit serializer, such as a shift register.
When a keyboard operator requests a transfer of data from the unit
12 to the display storage unit 11, the unit 12 locates the data in
the file and transfers it to the display storage unit 11 in the
appropriate video code. This usually requires code conversion since
data is preferably stored in the unit 12 in the standard ASCII
code. The data in video format entered into the display storage
unit 11 is synchronized with the CRT display unit 10, as by clock
and index pulses stored on separate tracks of the display storage
unit. In other words, the beam raster scan of the CRT display unit
10 operates in synchronism with the cyclic display storage
unit.
A detailed block diagram illustrating an embodiment of the present
invention will now be described with reference to FIG. 3 wherein
the CRT display unit 10, the file storage and control unit 12 and
the keyboard 13 are shown in block form only inasmuch as each may
be conventionally implemented, as in any one of several
commercially available CRT display systems. Accordingly, FIG. 3
shows in somewhat more detail only that part of the cyclic display
storage unit 11 which exemplifies the present invention and which
in practice, is an integral part of the file storage and control
unit 12 as noted hereinbefore. It should also be understood that
only so much of the display storage unit is shown in FIG. 3 as is
necessary to understand and practice the present invention.
Drum tracks 20 and 21 are dedicated for storage of video codes, one
video code consisting of eight bits for each stroke group of a
character. As noted hereinbefore with reference to FIG. 2, six
strokes are required for each character so that a total of 48
binary digits are stored on the tracks 20 and 21 for each
character, half on one track and the other half stored in parallel
on the second track. For instance, for the sixth stroke group, the
odd numbered bits are stored on the track 20 and the even numbered
bits are stored on the track 21. A single track could be employed
to store all bits in sequence, but two tracks are preferred to
avoid bit density problems on the magnetic record media. Four, or
even eight, tracks could also be used but with present recording
techniques, such would not be necessary. Moreover, the necessary
serializing of four or eight bits would be more complex.
Accordingly, a two-track display storage system is deemed to be the
optimum configuration, but future technology may make a one-track
system more feasible.
For convenience, the bit positions are indicated in FIG. 3 by the
arabic numerals 1 to 8, but it should be understood that in each
bit position only a binary "0" or a binary "1" is stored in
accordance with the code required for generation of the character
to be displayed. For instance, to display the letter N, the fourth
stroke group (see FIG. 2) would contain a binary ="1" in bit
position 3 and a binary "0" in all other bit positions 1, 2, 4, 5,
6 and 7. In the eighth bit position, either a binary "1" or a
binary "0" may be stored since the beam is blanked during the
eighth bit time of each stroke group, but in practice, a binary "0"
is stored unless nonvideo information is to be stored with the
video code group.
The beam is also blanked during all eight bit times of the sixth
stroke group so that, for video display purposes, it is not
material what binary digit is stored in each bit position, although
in practice a binary "0" is stored in each bit position unless it
is desired to store some nonvideo information. In accordance with
the present invention, a cursor signal is stored in one of the bit
positions of a sixth stroke group, preferably as a binary "1" in
bit position 6. Thus, by allocating one of the bit positions in a
sixth (intercharacter space) stroke group for storage of a cursor
signal, the next character position is marked as the video code
group into which a character may be entered. Accordingly, the
cursor position can be defined without the use of a separate track
to carry the cursor signal.
The sixth bit position of a sixth stroke group is preferably
utilized to store the cursor signal because as the cursor signal is
transferred from one character position to another, it is necessary
to erase the binary "1" in its present location and store a binary
"1" in the next location, without disturbing binary digits of the
video code in the new location. Therefore, because of flux fringing
which cannot be avoided, the bit positions on either side of the
cursor signal position should not be used. This requirement is
imposed by the high bit density (e.g., 680 bits per inch) employed
in the tracks 20 and 21. In a display storage unit having a lower
bit density, it would be possible to selectively alter a single bit
in any position without affecting bits stored in adjacent
positions, in which case there would be no restrictions on the bit
positions of the sixth stroke group selected for storing the cursor
signal.
The video codes of successive characters are read from the tracks
20 and 21 by read heads 23 and 24, and stored in sequential pairs
by buffer flip-flops FF.sub.1 and FF.sub.2, preferably JK
flip-flops triggered by clock pulses read from a clock pulse track
27 by a read head 28. Accordingly, the read head 28 generates four
clock pulses for each stroke. A bit counter 29 counts the four
clock pulses to generate distinct clock signals C.sub.1, C.sub.2,
C.sub.3 and C.sub.4 for each pair of video code bits read. The
clock pulses from the read head 28 are also applied directly to a
sampling pulse generator 30 which transmits a pair of strobe
signals B.sub.1 and B.sub.2 for each pair of stroke group bits read
by the heads 23 and 24 in order to transmit to the CRT display unit
10 the code group bits in proper serial sequence through sampling
gates 31 and 32. Strobe pulse B.sub.1 samples the binary digit
stored in the flip-flop FF.sub.1 to transmit to the CRT display
unit 10 the odd numbered bits of each stroke group via an OR gate
33, while a sampling pulse B.sub.2 similarly samples the even
numbered bits stored in flip-flop FF.sub.2. Thus, while the video
code for a stroke is read in pairs into buffer flip-flops FF.sub.1
and FF.sub.2 in response to clock pulses, the sampling pulse
generator 30 so responds to clock pulses as to cause each pair of
binary digits to be transmitted to the CRT display unit 10 in
series. Accordingly, flip-flops FF.sub.1 and FF.sub.2 function as a
parallel memory output register while gates 31 and 32 function as a
parallel-to-serial converter in response to sampling.
The bit counter 29 transmits the successive clock signals C.sub.4
to a stroke counter 34 which produces a signal S.sub.6 = during the
intercharacter space group of each character being displayed, as
shown in the timing diagram of FIG. 5. The signal S.sub.6 from the
stroke counter 34 enables an AND gate 35 to transmit to a flip-flop
FF.sub.4 any binary "1" stored in flip-flop FF.sub.2 from bit
position 6 of the sixth stroke group of each character being
displayed. If a cursor signal is stored in the sixth bit position
as described hereinbefore, the flip-flop FF.sub.4 is set and
thereafter reset by the leading edge of the next stroke signal
S.sub.6 as shown in the timing diagram of FIG. 5.
The true output terminal of the flip-flop FF.sub.4 is connected to
an AND gate 36. The output terminal of the AND gate 36 is in turn
connected to the CRT display unit 10 via the OR gate 33. In that
manner, the flip-flop FF.sub.4 will enable the display unit 10 to
produce a dot at each of the 35 positions of the following
character, i.e., during strokes 1 to 5 of the next character. If 35
dots were displayed during each cycle of the cyclic display storage
unit 11 (FIG. 1) comprising the magnetic drum tracks 20 and 21
shown in FIG. 3, they would completely obscure the character, if
any, being displayed. In order to display the cursor symbol without
obscuring the character to be displayed at the same position, the
gate 36 is further controlled by a counter 37 operative only a
fraction of the time the character being marked by a cursor signal
is to be regenerated on the face of the CRT. For example, the
counter 37 may consist of two binary circuits in cascade in order
to effectively divide the number of cursor signals displayed by
four, thereby rendering the gate 36 operative only every fourth
time the character being marked is to be regenerated. However,
instead of counting the cursor signal, which occurs only once
during each cycle of the track 21, a system synchronizing index
pulse is counted. That index pulse is stored on a separate track 38
and read by a head 39.
The gate 36 is also connected to the two output terminals of the
sampling pulse generator 30 by an OR gate 40 in order that
generation of dots for the display of a blinking block (i.e.,
cursor symbol) be synchronized by strobe signals B.sub.1 and
B.sub.2 in the same manner that generation of dots for the display
of a character is synchronized by the strobe signals B.sub.1 and
B.sub.2 through gates 31 and 32. However, it should be understood
that such synchronization, as well as other synchronization
indicated in FIG. 3, is a mere matter of design that depends upon
the manner in which the CRT display unit 10 is implemented, rather
than upon the concepts of the present invention. The same is also
to be understood of all synchronization indicated in FIG. 3 for the
file storage and control unit 12, bit counter 29 and stroke counter
34 shown connected to the read heads 28 and 39 for clock and index
pulses.
The flip-flop FF.sub.4 is set during the last half of the sixth
stroke if a cursor signal is present in bit position 6.
Accordingly, a dot would normally be produced during bit time 7 of
stroke 6 but, as noted hereinbefore, the beam of the CRT display
unit 10 is blanked during the entire period of the sixth stroke.
Consequently, dots are displayed in response to the output of the
flip-flop FF.sub.4 during each bit position of only strokes 1 to 5
of the following character positions (except the retrace bit
position 8 of each such stroke).
Once the operator observes which character position is available
for entry, as manifested by a blinking block in a character
position of the CRT display unit 10, and he decides to enter a
character in that position, he simply depresses the appropriate
character key on the keyboard 13. The file storage and control unit
12 then immediately accepts a code representing the character to be
entered and stores it in a buffer register until the cursor signal
is again read and sampled to set the flip-flop FF.sub.4, at which
time the cursor signal is erased from bit position 6 of the sixth
stroke group preceding the character position on the tracks 20 and
21 into which a new character is to be entered. Following that, the
file storage and control unit 12 enters the new character and
stores a binary "1" in bit position 6 of the sixth stroke group in
that character position into which the new character has just been
entered, thereby advancing the cursor signal to the next character
position as a character is entered. The cursor signal may also be
advanced to the next character position without entering a
character simply by depressing an appropriate key on the keyboard
unit 13.
The manner in which the file storage and control unit 12 controls
entry of a new character and advances the cursor signal from one
position to the next will now be described with reference to an
exemplary implementation illustrated in FIG. 4. When any key on the
keyboard unit 13 (FIG. 3) is depressed to enter a character, a
signal is transmitted to an input terminal 41 of an OR gate 42 to
enable an AND gate 43 to transmit a pulse from gate 35 (FIG. 3), as
indicated by the legend "GATE 35" at an input terminal of the AND
gate 43. That pulse 45 (shown in FIG. 5) is transmitted by the AND
gate 43 to control logic 44 of the file storage and control unit 12
which stores a binary "0" in the sixth bit position from which the
cursor signal was just read, thereby erasing the cursor signal.
That pulse is also transmitted by the AND gate 43 to a buffer
flip-flop FF.sub.5.
As shown in FIG. 5, the flip-flop FF.sub.5 is set during the period
of the pulse C.sub.3 of the sixth stroke if a cursor signal is
present in the sixth bit position and then reset by the next pulse
C.sub.3 via an AND gate 46. While the flip-flop FF.sub.5 is set, an
AND gate 47 is enabled in order that the next pulse C.sub.1 may set
a flip-flop FF.sub.6, but only if a character has been entered and
a signal is present at the input terminal 41. The flip-flop
FF.sub.6 remains on for five full strokes of the next character, as
shown in FIG. 5, and is then reset by the next stroke signal
S.sub.6. In that manner, the flip-flop FF.sub.6 transmits a signal
to a control logic network 49 that initiates entry of the character
selected by the operator in the position indicated by the cursor
signal just erased.
The output terminal of the flip-flop FF.sub.5 is also connected to
an AND gate 50 to enable it to set a flip-flop FF.sub.7 in response
to the next pulse C.sub.3, the same pulse C.sub.3 which resets the
flip-flop FF.sub.5. The flip-flop FF.sub.7 remains set until the
end of the fifth stroke period, at which time the next stroke
signal S.sub.6 enables an AND gate 52 to reset it in response to
the next pulse C.sub.4. Accordingly, the flip-flop FF.sub.7 remains
set until after the pulse C.sub.3 of the next stroke 6. While it is
set, the flip-flop FF.sub.7 enables an AND gate 53 to transmit a
pulse 51 (FIG. 5) to a logic network 54 in response to a pulse
C.sub.3 during the next stroke signal S.sub.6 to store a binary "1"
in the sixth bit position of the sixth stroke of the character
being entered.
The logic networks 44, 49 and 54 are connected to a pair of
recording amplifiers 55 and 56 which are connected to respective
write heads 57 and 58 associated with tracks 20 and 21 as shown in
FIG. 3. Accordingly, only the amplifier 56 connected to the head 58
receives recording signals from all three of the logic networks 44,
49 and 54 since a cursor signal is stored only in track 21. Both
heads 57 and 58 are so positioned on their respective tracks 20 and
21 as to allow for delays in causing binary digits to be recorded
through the logic networks 44, 49 and 54. In that manner, when a
new character is entered, it is properly entered in the character
position specified by the cursor signal and the cursor signal is
advanced one character position.
If the operator depresses a key to advance the cursor signal
without entering a character, a signal is transmitted to an input
terminal 60 of the OR gate 42 so that the same functions are then
initiated in the logic networks 44 and 54, but not in the logic
network 49 because the AND gate 47 connected to the set input
terminal of the flip-flop 48 is not then enabled by an input signal
from the terminal 41. If both keys are actuated at the same time,
the result is, of course, as though only the "enter character" key
is depressed Although not shown, the signals at input terminals 41
and 60 are provided by buffer flip-flops which are set when the
respective keys are actuated, and reset when the action indicated
thereby is complete so that, for example, the same character is not
entered automatically in all subsequent character positions of the
display storage. The character input register, also not shown, is
cleared at the same time, all in accordance with normal techniques
for interfacing digital equipment with a keyboard for entering
data.
From the foregoing, it should now be appreciated that a data
display system has been disclosed herein in which a cursor symbol
is displayed in response to a cursor signal selectively recorded in
otherwise unused portions of video data tracks instead of requiring
an extra cursor signal track. The cursor symbol is displayed by
superimposing it over a displayed symbol and causing it to
blink.
* * * * *