Abstract:
A screen display device which displays characters and patterns on a TV screen or other screen having a separate blanking signal output controlled by set data for each character in the display memory. Different displays can be shown on several different screens by controlling a color signal which combines the set data for each character and the set data for each screen.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to a screen display device for displaying characters and patterns on a TV screen or other device. 
     Recently, as TVs and VCRs have become more varied, more capable and more user friendly, it has become possible to use characters and patterns to display such information as the current channel and the operating mode on the screen. 
     FIG. 3 is a block diagram of the design of a conventional screen display device of this type. In FIG. 3, an H counter 1 counts the synchronization signal from the synchronization signal generator circuit (not shown), compares it with the data from the data bus, and detects the character display position. FIG. 3 also depicts screen display oscillator circuit 2; V counter 3 which counts the output clock of screen display oscillator circuit 2, compares it with data from the data bus, and detects the character display position; display position control circuit 4 which uses the outputs of H counter 1 and V counter 3 to control the position of the character display; timing generator 5 which controls the timing of the address counters etc. described below; address counter 6 which outputs the address of the display RAM (display memory) described below; display RAM 7 which stores the addresses of each display color data and character code that is the address of the character ROM (character memory) described below; character ROM 8 stores font data for display characters; shift register 9 converts the output signal of character display ROM 8 into serial data; color signal selection circuit 10 determines the mixing of color signals according to display color data from display RAM 7; bordering signal output circuit 11 outputs bordering data according to the display character font data stored in character ROM 8; shift register 12 converts bordering pattern data from bordering signal output circuit 11 into serial data; and image signal output circuit 13 which outputs a video signal, synchronized with the timing signal from timing generator 5, which comprises, depending upon the output of color signals based on the color signal from color signal selection circuit 10 and font data from character ROM 8 (outputs of shift registers 9 and 12), a red signal from the R (red) terminal, a green signal from the G (green) terminal, a blue signal from the B (blue) terminal, an intensity signal from the I (intensity) terminal, and a blanking signal which erases the background of the character from the OUT terminal and makes the border of a character. 
     Next the operation of the conventional device is explained. Display position control circuit 4 compares character display position data from the data bus connected to the CPU (not shown) with the values of H counter 1 and V counter 3 to determine the position at which a character is displayed on a screen. Next, according to the outputs of timing generator 5 and display control circuit 4, the contents of address counter 6 are incremented by one for each character and then character type data (address of character ROM 8) and character color data (mixing of the output color signal) which was entered previously in display ROM 7 is read. Color signal selection circuit 10 decodes the read color display data and the output color signal and the selection data are inputted to video signal output circuit 13. 
     If a border is to be added to the displayed characters, once the shift register 12 has converted the bordering data generated by bordering signal output circuit 11 using character font data from character ROM 8 into serial data b, the serial data b is synchronized with a timing signal from timing generator 5 and a video signal is outputted from the OUT terminal of video signal output circuit 13. In this way a border is created for characters which are displayed on television screens and other types of displays. 
     By repeating these operations, screen display data is gradually read out from display RAM 7 and character ROM 8 so that a video signal is outputted from video signal output circuit 13. 
     The conventional screen display device as described above can assign only one type of color signal and blanking signal to each character. Therefore, difficulties arise if two or more screens are displayed on a conventional screen display using a different character output method for each screen, as for example in the case of picture recording, one screen is the original video image, while information needed for the picture recording is displayed on the other screen. 
     SUMMARY OF THE INVENTION 
     The object of this invention is to provide a multi-purpose screen display device which, if two or more screens are used, can change the character output method for each screen in order to solve the problems described above. 
     According to one aspect of the invention there is provided a video display device which includes a memory area (14) in display memory (display RAM 7) for the display mode of each character for each of the several display screens; and a blanking signal control device (15) which, according to the set data, controls the output of the blanking signal to control the blanking signal output from terminal (OUT 2) provided in a video signal output circuit (13). 
     According to another aspect of the invention there is provided a video display device which includes, in addition to the above, a setting device (register 16) which sets the display mode of each screen; and a color signal control device (18) which controls whether or not a color signal is outputted according to the preset data from memory area (14) in the display memory (display RAM 7) and the aforementioned preset display mode data. 
     The above and other objects, features, and advantages of this invention will become more apparent from the following description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a screen display device according to an embodiment of the first invention; 
     FIG. 2 is a block diagram of a screen display device according to another embodiment of the second invention; and 
     FIG. 3 is a block diagram of a conventional screen display device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1, a screen display device according to an embodiment of the invention is shown. The parts corresponding to parts of FIG. 3 are represented by the same symbols and are not explained here. The screen display includes a one bit memory area 14 added to each of the addresses in display RAM 7 in which the desired display data for each character is set; a blanking signal control device 15 which, depending upon the data set in memory area 14 of display RAM 7, separately controls whether a blanking signal is outputted which controls character erasure and character bordering; the blanking signal control device 15 consisting of an AND gate 15a which takes the logical product of the set data from memory area 14 of display RAM 7 and of the output signal (OUT&#39;) of color signal selection circuit 10. This output signal of AND gate 15a is outputted through video signal output circuit 13 as second blanking signal from the newly set OUT 2 terminal. 
     Next, the operation of the screen display device of FIG. 1 is explained. This screen display device is identical to the conventional screen display device of FIG. 3 excepting output signal (OUT&#39;) from color signal control circuit 10 which controls the blanking signal and a second blanking signal (OUT 2). Video signal output circuit 13 controls the output of this second blanking signal according to the output signal of AND gate 15a, which takes the logical product of output signal (OUT&#39;) and the set data c, newly set for this embodiment, from memory area 14 of display RAM 7, and synchronizes the second blanking signal with the timing signal from timing generator 5. The characteristics of this embodiment are explained below. 
     For example, if characters are displayed on two screens, an intensity signal (I) and a blanking signal (OUT) are inputted to one screen (a monochrome screen for example) and color signals (R,G,B) and a blanking signal (OUT2) are inputted to the other screen (a color screen for example). Accordingly, even though the same characters are displayed on the two screens, if the background of the color characters on the color screen need not be erased or if bordering of those characters on the color screen is not necessary, then by setting the value of the memory area 14 of display RAM 7 to logical zero, the blanking signal outputted from OUT 2 terminal of the video signal output circuit 13 is cancelled and characters having a background or unbordered characters can be displayed as desired. Moreover, if the value of the memory area 14 is set to 1, then the output signal (OUT&#39;) of color selection circuit 10 is outputted as is from AND gate 15a. Thus the OUT 2 terminal of the video signal output circuit 13 outputs the same blanking signal which was previously outputted from the OUT terminal. In this case, characters which have erased backgrounds or bordered characters are displayed on a color screen. 
     Since the video signal output circuit 13 has a blanking output controlled by the data set in the display RAM 7, it is possible to select the presence of a blanking output for each screen or character. 
     FIG. 2 shows a screen display device according to another embodiment of the invention, wherein elements corresponding to the elements of FIG. 1 are indicated by the same symbols and are not explained here. This screen display device includes one-bit register 16 (set device) which stores data indicating whether to output a color signal to each screen from the data bus connected to the CPU (not shown); and a color signal control device 18 which, depending upon the output signal produced by mixing the set data from memory area 14 of display RAM 7 which controls blanking signal control device 15 with the set data from register 16, controls whether a color signal output is sent to video signal output circuit 13 from color selection circuit 10. Color signal control device 18 is composed of OR gate 18d which takes the logical sum of set data d of register 16 with set data c of memory area 14 in display RAM 7 as well as AND gates 18a, 18b and 18c which take the logical product of each output signal (color signal) of color selection circuit 10 with the output signal e of the OR gate 18d. 
     Next the operation of the screen display device shown in FIG. 2 is explained. This screen display device operates the same way as the embodiment of FIG. 1 except that color signals are outputted from terminals R, G, and B of video signal output circuit 13 after the signal output from the color signal selection circuit 10 is controlled by the AND gates 18a, 18b, and 18c in response to the output e from the OR gate 18d which takes a logical sum of the data d from the register 16 in which information for designating the presence of a color signal from the data bus and the data c from the memory area 14 of the display RAM 7 which controls the second blanking signal output at the OUT 2 terminal from the video signal output circuit 13. The operation of the embodiment shown in FIG. 2 are explained below. 
     If the value of register 16 is set to logical 1, then the output signal e of OR gate 18d is logical 1, and the color signals (R,G,B) outputted by the color signal selection circuit 10 are sent unchanged through AND gates 18a, 18b and 18c to video signal output circuit 13 so as to display characters, etc. on a color display. Moreover, if register 16 is set to logical 0, then the output signal e of OR gate 18d becomes the same as the data in memory area 14 in display RAM 7. ANDing this data with the output signal of color signal selection circuit 10 by AND gates 18a, 18b, and 18c controls the color signal which is outputted at the R, G, and B terminals of video signal output circuit 13. 
     For example, if characters are displayed on two screens, an intensity signal (I) and a blanking signal (OUT) are inputted to one screen (a monochrome screen for example) and color signals (R,G,B) and a blanking signal (OUT2) are inputted to the other screen (a color screen for example). Accordingly, even though the same characters can be displayed on the two screens, if there is a character which you do not want to display on the color screen, then by setting register 16 to logical 0 and setting the value of memory area 14 of display RAM 7 to logical 0, the output signals of AND gates 18a, 18b, and 18c go to logical 0, the color signals (R,G,B) are not outputted, and the character is not displayed. 
     As shown by the embodiment of FIG. 2, the video signal output circuit 10 can be controlled by the color signal generated by combining the set data in display RAM 7 with the set data in register 16. This makes it possible to select whether or not to output a color signal to each screen and to each character, that is, whether to output a given character. 
     Although the case of two blanking signals for two screens is described in the embodiments above, three screens (all color screens) can be accommodated by the control device employed in this design by increasing the number of set bits and of blanking signal output terminals and by setting three or more blanking signals. Moreover, although AND gates are used as the blanking signal control device in the embodiments above, the same function can be performed by other logic circuits. 
     According to one aspect of the invention, as described above, since several separate outputs are provided for the blanking signals controlled by data from display memory, if data is displayed on two or more screens, the character output method can be changed in single character units depending upon whether or not a blanking signal is outputted. This increases the potential applications of the screen display device. 
     Moreover, according to another aspect of the invention, because it has a configuration which controls whether a color signal is outputted depending upon the data created by combining data from the display memory with data from a fixed device, if data is to be displayed on two or more screens, the character output method can be changed in single character units depending upon whether or not each blanking signal is outputted. Moreover, by using the combined data to control whether or not a color signal is outputted as described above, characters displayed on each screen can be selected in single character units. This increases the range of applications for this screen display device.