Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a display
device. More particularly, the present invention relates
to a display device in which a dynamic picture and a still
picture are displayed simultaneously or selectively on the
screen of a CRT display.
Recently, television te~t broadcast has been
realized and apparatus for receiving such television text
broadcast has been put into practical use. As one form of
such television text broadcast, teletext is known. A
technical document well known in the art concerning such
teletext receiving apparatus is "LSI circuits for teletext
and view data" (THE LUCY GENERATION, Mullard Technical
Publication M81-0001).
In the accompanying drawing:-
Figure 1 is a schematic block diagram showing a
display device in a conventional teletext receiving
apparatus; and
Figure 2 is a schematic block diagram of an
embodiment of the present invention.
Referring to Figure 1, a display device in a
conventional teletext receiving apparatus will firstly be
described. As shown, a CPU 1 is connected to a frame
memory 2 and an offset register 6. The frame memory 2 has
a display area corresponding to the screen of a CRT
display 5 and stores picture data to be displayed. The
offset register 6 stores the first address of the frame
memory 2 provided from the CPU 1. The first address
stored in the offset register 6 is supplied to one input
of an adder 7, while a read address of the frame memory 2
is supplied to the other input of the adder 7 from a
controller 4.
The adder 7 adds up the first address supplied
from the offset register 6 and the read address supplied
from the controller 4 so as to designate an address in the
frame memory 2. A still picture signal A based on the
picture data read out from the frame memory 2 for
displaying a still picture is supplied to a selector 3.
To the selector 3, a dynamic picture signal B for
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displaying a dynamic picture is supplied from the exterior
through an input terminal 12. The selector 3 is switched
by a selection switch 8 so that either the dynamic picture
signal B entered from the input terminal 12 or the still
picture signal A based on the picture data read out from
the frame memory 2 is supplied to the CRT display 5.
Now, the operation of the display device in the
conventional teletext receiving apparatus will be
des~ribed. First, the CPU 1 makes the offset register 6
store the address corresponding to the first scanning line
of the screen of the CRT display 5. The adder 7 adds up
the address stored in the offset register 6 and the read
address supplied from the controller 4 so as to designate
addresses in the frame memory 2 corresponding to the first
scanning line of the screen. In response to the
designation of the addresses, the frame memory 2 reads out
successively a still picture signal A. The still picture
signal A is supplied to the selector 3.
On the other hand, in synchronism with the still
picture signal A read out from the frame memory 2, the
dynamic picture signal B entered from the exterior through
the input terminal 12 is supplied to the selector 3.
Either the still picture signal A or the dynamic picture
signal B is selected by the selector 3 according to the
swit~hing of the selection switch 8. Thus, the selected
one of the pictures, namely, either the still picture or
the dynamic picture is displayed on the-CRT display 5.
In the display device shown in Figure 1, if the
selection switch 8 selects the still picture signal A, the
adder 7 adds to or subtracts from the first address stored
in the offset register 6, the address from the controller
~, whereby the first address value read out of the frame
memory 2 can be changed according to the screen for
display and thus, display can be made on a scrolled
screen.
However, the above stated display device can
only display, by selection, either a dynamic picture or a
still picture on the CRT display 5 but cannot display
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simultaneously a dynamic picture and a still picture in
divided areas on the CRT display 5. As a result, the
above stated conventional display device has a drawback in
that a dynamic picture and still picture associated with
each other cannot be displayed simultaneously so that a
viewer may compare or examine them.
It is accordingly an object of the present
invention to provide a display device in which a still
picture and a dynamic picture can be displayed in display
areas on a CRT display and in which a scrolled picture can
be displayed in the still picture display area.
Briefly stated, in the present invention, a
value representing a horizontal border line horizontally
dividing display areas on the screen of the CRT display is
determined in advance by setting means so that pictures
may be displayed in separate display areas. Then, a
synchronizing signal is counted and the count value and a
value set by the setting means are compared. In response
to the comparison output signal, the screen of the CRT
display is horizontally divided into the display areas, so
that a picture based on a video signal applied to an input
terminal and a picture based on the picture data read out
from a frame memory are selected by selecting means and
displayed in the divided areas on the CRT display.
Consequently, according to the present
invention, display areas on the screen of the CRT display
are divided and a video signal based on a picture to be
displayed on a divided display area is selected according
to the data representing the horizontal border line of the
divided display areas and thus, a dynamic picture and a
still picture can be displayed simultaneously in the
divided display areas. In addition, only the still
picture can be scrolled in its display area and
accordingly, the display function can be improved, which
will lead to wider utilization.
The invention will be more readily understood
from the following description of the preferred embodiment
thereof illustrated by way of example in Figure 2.
In Figure 2, the CPU 1, the frame memory 2, the
selector 3, the offset register 6 and the adder 7 are the
same as shown in Figure 1. The controller 4 is structured
so as to generate a horizontal synchronizing signal in
synchronism with a video signal based on the picture data
read out from the frame memory 2. The horizontal
synchronizing signal generated from the controller 4 is
supplied to~the counter 9.
The counter 9 counts the horizontal
synchronizing signal and supplies the count output to the
comparator 11. The selection value register 10 stores a
selection value representing a horizontal border line of
the display areas divided hori~ontally on the screen of
the CRT display 5. This selection value is supplied from
the CPU 1 to the selection value register 10. The
selection value stored in the selection value register 10
is supplied to the comparator 11. The comparator 11
compares the selection value supplied from the selection
value register 10 with the count output from the counter 9
and provides the output of comparison to the selector 3.
The selector 3 divides display areas on the screen of the
CRT display 5 based on the output of comparison from the
comparator 11, so that a picture based on the still
picture signal A read out from the frame memory 2 is
displayed in one of the divided display areas and a
picture based on the dynamic picture signal B entered
through the input terminal 12 is displayed in the other
display area.
In the following, the operation of a display
device in accordance with the preferred embodiment of the
present invention will be described.
The CPU 1 stores the selection value in the
selection value register 10 and stores the first address
of the frame memory 2 in the offset register 6. The first
address of the frame memory 2 stored in the offset
register 6 is supplied to the adder 7. The adder 7 adds
the read address supplied from the controller 4 to the
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first address so as to designate successively addresses of
the frame memory 2.
The controller 4 generates the horizontal
synchronizing signal and supplies it to the counter 9.
The counter 9 counts the horizontal synchronizing signal
and supplies the count output to the comparator 11. The
comparator 11 compares the count value C of the counter 9
with the selection value D stored in the selection value
register 10 and based on the output of comparison, the
selector 3 is controlled so that a dynamic picture and a
still picture are displayed respectively in the two
different display areas on the screen of the CRT display
5.
More specifically, in case where the count value
C of the counter 9 is smaller than the selection value D,
the selection signal S from the comparator 11 is S=l. The
selector 3 selects the dynamic picture signal B entered
from the input terminal 12 based on the selection signal
S=l and supplies the dynamic picture signal B to the CRT
display. As a result, in the upper display area on the
screen of the CRT display 5, a dynamic picture based on
the dynamic picture signal B is displayed. When the
counter 9 counts the horizontal synchronizing signal and
the count value C of the counter 9 becomes larger than the
selection value D, the selection signal from the
comparator 11 is S=0. Then, based on the selection signal
S=0, the selector 3 selects the still picture signal A
read out from the frame memory 2 so that a still picture
based on the still picture signal A is displayed in the
lower display area on the screen of the CRT display 5.
Thus, a dynamic picture and a still picture are displayed
simultaneously in the respective display areas divided
.orizontally on the screen of the CRT display 5.
The horizontal synchronizing signal counted by
the counter 9 can be separated in synchronism directly
from the video signal entered from the exterior through
the input terminal 12.
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Although in the above described embodiment, the
screen of the CRT display 5 is divided into two display
areas with a comparator 11 and a selection value register
10 being provided, a plurality of comparators 11 and
selection value registers 10 may be provided and in this
case, by applying the count value of the horizontal
synchronizing signal to the respective comparators 11 and
storing different selection values in the selection value
registers 10, different pictures can be displayed in a
plurality of display areas divided on the screen of the
CRT display 5.
In addition, although in the above-described
embodiment, the selector 3 selects the dynamic picture
signal B with the relation between the count value C of
the counter 9 and the selection value D of the selection
value register 10 being C<D and selects the still picture
signal A with the relation being C>D, the selector 3 may
select, on the contrary, ~he dynamic picture signal B with
the relation of C>D and the still picture signal A with
the relation of C<D.
Although a preferred embodiment of the present
: invention has been described and illustrated in detail, it
is clearly understood that the same is given by way of
illustration and example only and is not to be taken by
way of limitation, the spirit and scope of the present
invention being limited only by the terms of the appended
claims.
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