Combined graphic and textual display system

A display system comprises a first image memory storing first image data, a second image memory storing second image data operable independently from the first image memory, a display selection and combination circuit, and two display units. The display selection and combination circuit connected to the first and second image memories is formed such that each of the display units displays a combination of data from the image memories according to a display request. Normally, the display units are cathode ray tubes or liquid crystal displays. Usually, one of the first and second image memories stores character information, such as letters and numerals, and the other stores graphic information, such as figures and curves.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a display system capable of selectively 
displaying graphic display data and character display data and a 
combination of the two types of data on two display units. 
2. Description of the Prior Art 
In recent years, display systems have become increasingly advanced. Even 
personal computers are now being provided with display systems capable of 
the display of not only character information, such as letters and 
numerals, but also graphic information, such as figures, curves, circle 
graphs, and histograms. 
The display of an actual graph requires the combination of graphic and 
character information. In the prior art, this has been achieved by storing 
the combined graphic display data and character display data in an image 
memory having a capacity sufficient for a display picture and by 
displaying the data on a single cathode ray tube (CRT). The prior art, 
however, has suffered from the problem of inadvertent deletion of 
characters due to interference from the graphic display when adjusting the 
display, for example, changing colors, enlarging figures, and changing 
positions, and the problem of an overly crowded display picture when there 
are too many characters and symbols for graph notations. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a display system able to 
display graphic data and character data individually or in combination, 
preventing inadvertent deletion of character data due to interference from 
graphic data or vice versa, and presenting a visually simple display 
picture. 
In accordance with the present invention there is provided a display system 
which includes a first image memory storing first image data; a second 
image memory storing second image data; and a display selection and 
combination device connected to the first and second image memories. The 
display selection and combination device has two output terminals 
connectable to two independent display units, through which the display 
selection and combination device outputs two display signals selected from 
the first and second image data in response to a control signal or at 
least one display signal mixing the first and second image data in 
response to the control signal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As illustrated in FIG. 1, a display system in accordance with the present 
invention comprises a central processor unit (CPU) 1, a timing controller 
(CNT) 2, a graphic image memory (GM) 3, a character image memory (CM) 4, a 
character generator (CG) 5, a display selection and combination circuit 
including a control register (REG) 6 and a display selection circuit (SW) 
7, CRT display units CRT1 and CRT2, and video signal converting circuits 
(VD) 8A and 8B. The above elements are connected to each other by means of 
a data bus DB, address buses AB1 and AB2, and other buses illustrated in 
FIG. 1. In this embodiment, data to be displayed are first processed in 
the CPU. Graphic data, such as figures are stored in the graphic image 
memory 3 through the timing controller 2. Character data, such as letters, 
symbols, and numerals are stored in the character image memory 4. Both 
image memories store the above data in the form of a dot-pattern. 
It should be noted that, in the case of character data, only codes 
corresponding to the characters are stored in the character image memory 
4. The above codes are transformed into the dot-pattern signals 
corresponding to the actual characters recorded in the character generator 
5, for example, a read only memory (ROM). The data stored in the image 
memories 3 and 4 are serially output, in response to addresses on the 
address buses AB1 and AB2 supplied by the timing controller 2, to the 
display selection circuit 7 and finally displayed on the CRT display unit 
CRT1 and/or CRT2 through the video signal converting circuits 8A and/or 
8B. 
The display content can be selected or changed by keyboard operation or the 
like. In response to the keyboard operation, the CPU 1 sends a selection 
signal to the control register 6 through the data bus DB or a display 
command to the timing controller 2. The storage operation of the image 
memories 3 and 4 may occur at the desired times, such as at predetermined 
intervals, at the time of data changes, or only upon request. Therefore, 
the display may be updated at any desired time. 
A feature of the present invention is that any display can be obtained on 
the CRT displays by changing the selection data in the control register 6 
provided by the CPU 1. This will be made clear through the following 
explanation. 
In this embodiment, the control register 6 is a four-bit register and, 
therefore, can be used for the selection of 16 combinations of displays in 
accordance with to its control status, as listed in Table 1. In Table 1, 
"G. ACT" and "C. ACT" respectively stand for a graphic display activate 
command and a character display activate command. When G. ACT is "1", a 
graphic display may be provided to the corresponding CRT. On the other 
hand, when C. ACT is "1", a character display may be provided to the 
corresponding CRT. In Table 1, furthermore, GRAP. designates a graphic 
display, CHR. a character display, and GRAP. +CHR. a combined graphic and 
character display. For example, when the control status is "1001", a 
graphic display can be presented on the CRT display unit CRT1 and a 
character display on CRT2. When the status is "1101", a combined graphic 
and character display can be presented on the CRT display unit CRT1 and a 
character display on the CRT display unit CRT2. 
TABLE 1 
______________________________________ 
Control signal status 
CRT 1 CRT 1 CRT 2 CRT 2 
G. C. G. C. 
ACT ACT ACT ACT Display status 
______________________________________ 
0 0 0 0 CRT 1 No display 
CRT 2 No display 
1 0 0 0 CRT 1 GRAP. 
CRT 2 No display 
0 1 0 0 CRT 1 CHR. 
CRT 2 No display 
1 1 0 0 CRT 1 GRAP. + CHR. 
CRT 2 No display 
0 0 1 0 CRT 1 No display 
CRT 2 GRAP. 
1 0 1 0 CRT 1 GRAP. 
CRT 2 GRAP. 
0 1 1 0 CRT 1 CHR. 
CRT 2 GRAP. 
1 1 1 0 CRT 1 GRAP. + CHR. 
CRT 2 GRAP. 
0 0 0 1 CRT 1 No display 
CRT 2 CHR. 
1 0 0 1 CRT 1 GRAP. 
CRT 2 CHR. 
0 1 0 1 CRT 1 CHR. 
CRT 2 CHR. 
1 1 0 1 CRT 1 GRAP. + CHR. 
CRT 2 CHR. 
0 0 1 1 CRT 1 No display 
CRT 2 GRAP. + CHR. 
1 0 1 1 CRT 1 GRAP. 
CRT 2 GRAP. + CHR. 
0 1 1 1 CRT 1 CHR. 
CRT 2 GRAP. + CHR. 
1 1 1 1 CRT 1 GRAP. + CHR. 
CRT 2 GRAP. + CHR. 
______________________________________ 
Below is a simplified example where the control status is "1101" and CRT1 
and CRT2 are color CRT's having the three fundamental colors of red(R), 
green(G), and blue(B). FIG. 2 (a) illustrates graphic data comprising a 
circle graph on a CRT display unit, FIG. 2 (b) is character data 
comprising graph notations; FIG. 2(c) a combination of the two. The 
indications (B), (R), (G) and (Y) in the circle graph in FIGS. 2a and 2c 
represent that the segments are colored blue, red, green, and yellow, 
respectively. 
FIG. 3 is a circuit diagram of the connection between the control register 
6 and the display selection circuit 7. In FIG. 3, the display selection 
and combination circuit 7 consists of two signal mixing circuits MXl and 
MX2, the outputs of which are connected to the CRT display unit CRT1 and 
CRT2 through the video signal converting circuits 8A and 8B, respectively. 
The signals CRT1.G.ACT and CRT1.C.ACT and the signals CRT2.G.ACT and 
CRT2.C.ACT from the control register 6 are supplied to the input terminals 
of the signal mixing circuits MX1 and MX2, respectively. Three image 
signals G. BLUE, G. RED, and G. GREEN for the graphics output from the 
graphic image memory 3 and three image signals C. BLUE, C. RED, and C. 
GREEN for the characters output from the character image memory 4 are also 
supplied to the input terminals of the circuits MX1 and MX2. 
FIG. 4 is a detailed circuit diagram of an example of the signal mixing 
circuits MX1 and MX2. In FIG. 4, gates G1, G5, and G9 represent AND gates; 
gates G2, G6, and GlO NAND gates; gates G3, G7, and G11 inverters; and 
gates G4, G8, and G12 OR gates. Gates G13 through G24 in the signal mixing 
circuit MX2 use the same symbols as the above. 
Since the control status is "1101", CRT1.G.ACT, CRT1.C.ACT and CRT2.C.ACT 
are "1" and CRT2.G.ACT is "0". In this case, C. BLUE applied to the NAND 
gate G2 in the circuit MX1 is inverted by CRT1.C.ACT being equal to "1", 
inverted again at the inverter G3, and applied to one of the input 
terminals of the OR gate G4. In addition, since CRT1.G.ACT is "1", G. BLUE 
applied to the AND gate G1 is output to another input terminal of the OR 
gate G4 when the output of the NAND gate G2 is not a logical "1", i.e., C. 
BLUE is not "1". Therefore, the signal CRT1 BLUE at the output of the OR 
gate G4 is the combination of the above-mentioned G. BLUE and C. BLUE. 
When G. BLUE and C. BLUE are both "1", CRT1 BLUE represents C. BLUE rather 
than G. BLUE by operation of gates G1, G2 and G3. In other words, the 
direct path of C. BLUE through the inverter G3 acts as a priority 
selection of the character display which prevents deletion of character 
information by the graphic display when the graphic display interferes 
with the character display portions. CRT1 RED and CRT1 GREEN are output by 
the circuit MX1 after being formed in the same manner as CRT1 BLUE. 
On the other hand, since CRT2.G.ACT is "0" and CRT2.C.ACT is "1", G. RED, 
G. BLUE, and G. GREEN are inhibited at the AND gates G13, G17 and G21, 
while C. RED, C. BLUE and C. GREEN are output through OR the OR gates G16, 
G20 and G24 to form CRT2 RED, CRT2 BLUE, and CRT2 GREEN, respectively. 
As mentioned above with reference to the drawings, when the control status 
is "1101", the combined display illustrated in FIG. 2(c) is presented on 
the color CRT1, and the character display illustrated in FIG. 2(b) is 
presented on the color CRT2. The combined display in FIG. 2(c) is a 
mixture of the graphic display in FIG. 2(a) and the character display 
shown in FIG. 2(b). but the character display dots overlay the graphic 
display dots where both exist in the same position on the CRT. 
As can be easily understood, various combinations of displays on the CRT1 
and CRT2 are possible, as indicated in Table 1. 
In the above explanation, the CRT display units CRT1 and CRT2 were both 
color CRTs. They may, however, be both monochrome CRT display units or any 
combination of the same, as listed in Table 2. 
TABLE 2 
______________________________________ 
CRT 1 CRT 2 
______________________________________ 
Color Color 
Color Monochrome 
Monochrome Color 
Monochrome Monochrome 
______________________________________ 
When the CRT display units CRT1 and CRT2 are both monochrome, simpler 
signal mixing circuits as illustrated in FIG. 5 can be used. In FIG. 5, 
the symbols which are the same as those used in FIG. 4 designate the same 
type of gates as in FIG. 4. 
In the embodiment set forth with reference to FIG. 1, a graphic image 
memory and character image memory were used. The memories may, however, be 
both graphic image memories or both character image memories, as listed in 
Table 3. 
TABLE 3 
______________________________________ 
First image memory Second image memory 
______________________________________ 
Graphic Character 
Graphic Graphic 
Character Graphic 
Character Character 
______________________________________ 
According to the signal mixing circuits illustrated in FIGS. 4 and 5, the 
character display is given priority over the graphic display by means of 
the priority selection element, i.e., the inverter G3, when the displays 
interfere with each other on a display unit. The graphic display, however, 
may be given priority over the character display by a minor change in the 
above circuits. 
According to the present invention, when a person displays information, 
such as a distribution of sales, to a third person, such as a manager, he 
requests a display used for selecting the control command on CRT2 by using 
a keyboard, then requests a graphic display on CRT1 through the display on 
CRT2. Accordingly, the third person can easily read the desired 
information without the control data used by the initiator of the display. 
In addition, the program execution can be displayed on CRT1 and the 
program list displayed on CRT2. The CRT display units CRT1 and CRT2 can be 
arranged in any position, for example, can be arranged near each other or 
apart from each other. 
The display system according to the present invention is not limited to CRT 
display units, but can be applied to any display devices, such as liquid 
crystal devices and plasma display devices.