JPH04349794A - On-screen display circuit for video display device - Google Patents

Abstract

PURPOSE:To prevent a change in a size of a character or a symbol displayed on the screen as a video signal attended with a horizontal scanning frequency mode in the video display device on which a video signal of plural modes whose horizontal scanning frequency differs is displayed. CONSTITUTION:A read only memory 25 storing character or symbol fonts to be displayed in a display control section 13 is divided into two, character font data of 18 scanning lines are stored in addresses designated by an output data in a video memory and character font data of 15 scanning lines are stored in other addresses in advance, and a signal resulting from counting a synchronizing signal separated from an input video signal and from being discriminated by a horizontal scanning line number within one vertical scanning period is used to read the character font data of 18 scanning lines in the mode whose horizontal scanning frequency is 17.75kHz and to read the data of the same scanning line from the character font data of 15 scanning lines and the character font data of 18 scanning lines twice repetitively in the mode whose horizontal scanning frequencies are 24,43kHz and 31.5kHz respectively and the result is outputted as a display signal.

Description

[Detailed description of the invention]

0001

TECHNICAL FIELD The present invention relates to equalizing the size of characters or symbols displayed on-screen to be superimposed on an input video signal in each mode in a video display device capable of displaying video signals in a plurality of modes having different horizontal scanning frequencies.

0002

[Prior Art] In a mode in which the horizontal scanning frequency is doubled, character or symbol data to be displayed is used as an address signal, and character font data corresponding to one scanning line of a read-only memory is read out as character font data. was read out twice and output to two adjacent scanning lines. However, in horizontal scanning frequency modes that are not related to multiples, it is possible to use a read-only memory for character fonts for each horizontal scanning frequency mode, or to use an integrated circuit in the display control section that has a built-in character font memory. The same integrated circuit was used for each horizontal scanning frequency mode.

0003

[Problem to be Solved by the Invention] In a system that uses a read-only memory for character fonts corresponding to each mode or an integrated circuit for a display control unit for each mode in which the horizontal scanning frequencies are not related to each other, it is necessary to There were many points, and the cost was high.

0004

[Means for Solving the Problems] In a video display device as a display of a television tuner or a personal computer, the types of characters or symbols that can be displayed on screen are limited, and the integrated circuit of the display control unit, such as the μPD6451, It has a built-in read-only memory that stores character fonts of 112 types of characters or symbols, and has sufficient capacity for the types of characters or symbols required. The read-only memory is divided to store the minimum necessary character fonts of characters or symbols, one side stores the basic character fonts for modes that are related to double speed, and the other side stores the character fonts for modes that are not related to double speed. The basic character font is memorized, the horizontal and vertical synchronization signals are counted and the number of scanning lines in one field is determined, and each area of the memory divided by the signal is selected and the size corresponding to the horizontal scanning frequency mode is selected. Outputs the display signal.

[0005]

[Operation] Standard TV system with horizontal scanning frequency of 15.75kHz and vertical scanning frequency of 60Hz, horizontal scanning frequency of 31.5kHz.
EDTV system with a vertical scanning frequency of 60 Hz or horizontal scanning lines 480 personal computer display systems, and a video displaying signals of 400 personal computer display systems with a horizontal scanning frequency of 24.43 kHz and a vertical scanning frequency of 55 Hz. This will be explained using a display device as an example. The horizontal scanning frequency 15
．． In a personal computer display system corresponding to a standard TV system with a vertical scanning frequency of 75 kHz and 60 Hz, the number of horizontal scanning lines in one field is 240.

[0006] In order to make the height of characters or symbols displayed on-screen at each horizontal scanning frequency almost constant,
It is necessary to keep the number of lines "N" displayed on one screen constant. Furthermore, if the number of scanning lines constituting one character is assumed to be 18 for ease of viewing characters displayed on-screen in a standard TV system, then the number of display lines "N" on one screen is N=240/
It will be 18. Therefore, the number of scanning lines constituting one character of each horizontal scanning frequency is 15.75 kHz: 240/N=1824.43
kHz: 400/N=400×18/240=3
0 31.5 kHz: 480/N=480×18
/240=36.

[0007] Horizontal scanning frequency 15.75kHz and 31
．． 5kHz is double the speed, so 15.75kHz
By repeatedly reading out the character font for each scanning line twice, it is possible to obtain a signal of a character font of 36 scanning lines. In a mode with a horizontal scanning frequency of 24.43 kHz, the number of scanning lines that make up one character is 30, so by reading out a character font with 15 scanning lines that make up one character twice, a character font with 30 scanning lines can be read. Signal. Since the character font when the horizontal scanning frequency is 15.75kHz has 18 scanning lines, 15.
The scanning line character font can be compressed by about 83%, so even if it is stored in the same memory under the same conditions as the 18 scanning line character font, less memory space will be wasted.

18 scanlines and 15 of the character font
An example of a scan line is shown in FIG. Therefore, the read-only memory for storing character fonts is divided, character fonts of the same character or symbol are stored in one part, a character font with 18 scanning lines, and the other part, a character font with 15 scanning lines. The area is selected by a signal determined by counting the synchronization signals of the input video signal. Differences in character size on horizontal scanning lines due to differences in horizontal scanning frequency can be easily corrected by switching the frequency of the clock signal that generates the on-screen display signal 13a.

The horizontal scanning frequency is determined by a mode discriminating circuit 27 shown in FIG. 2, which resets it using a vertical synchronizing signal 12a separated from the input video signal, and by a counter 30 that counts the horizontal synchronizing signal 12b. The number of horizontal scanning lines is counted, and the output determined by the decoder 31 of the counted value at the start edge of the vertical synchronizing signal 12a is stored in the latch memories 35 and 36, respectively, and a discrimination signal 27a is generated based on the change in the counted value during counting. Prevent fluctuations in The counter 30
256 to 271 scanning lines are detected by ANDing the inverted output of bit 4 and bit 8 counted in the upper direction from "0" of the output, and 38 scanning lines are detected by ANDing bit 7 and bit 8.
4 to 511 scan lines are detected.

0010

[Embodiment] In the block diagram of the video display device shown in FIG.
supply to. The vertical synchronization signal 12a and horizontal synchronization signal 12b output from the synchronization separation section 12 are supplied to the deflection circuit, and a display signal 13a for on-screen display is also supplied.
It is also supplied to the display control section 13 which outputs the . The control unit 14 reads a key operation signal from the key input unit 15 of the video display device, decodes the operation signal, outputs a specified control signal, and controls the corresponding controlled circuit.

Along with the output of the control signal of the control section 14, character/symbol data 14a representing the control state of the control section 14 or the operating state of the controlled circuit and position data 14b on the display screen are generated, and the display control section 13. The display signal 13a outputted from the display control section 13 is supplied to the signal synthesis section 11, which superimposes the display signal 13a on the video signal input to the input terminal 10 and supplies it to the cathode ray tube via the video output circuit.

In the display control section 13 shown in FIG.
The display position data 14b outputted by the controller 14 is supplied to the video memory 24 via the selector 23 as an address signal, and the data 14a outputted simultaneously by the controller 14 is supplied to the data input and stored at a designated address. The synchronization separation section 12
The output of the clock oscillation circuit 20 synchronized with the horizontal synchronization signal 12b output from the synchronization separator 12 is counted by counters 21 and 22 synchronized with the vertical synchronization signal 12a and horizontal synchronization signal 12b output from the synchronization separation section 12. The outputs of 21 and 22 are used as address signals to switch the selector 23 and supply them to the video memory 24, and read out the data stored at the designated address.

The character font corresponding to the data read from the video memory 24 is supplied as an address signal to the read-only memory 25 stored therein, and the data of the character font corresponding to the input data is read out to the serial/parallel conversion circuit 26. A display signal 13a equivalent to a video signal is outputted via the video signal. The vertical and horizontal synchronization signals 12a and 12b input to the display control unit 13 are also supplied to the mode discrimination circuit 27, and the horizontal scanning frequency of the video signal input to the video display device is determined from the vertical and horizontal synchronization signals 12a and 12b. Determine the mode.

That is, the horizontal synchronizing signal 12b is supplied to the clock input of the counter 30 shown in FIG. 2, the vertical synchronizing signal 12a is supplied to the reset input of the counter 30, and the horizontal synchronizing signal 12a within one vertical scanning period Count. The output of the counting output of the counter 30 from the inverter 33 of bit 4 counted upward from "0" and the output of bit 8 are supplied to the AND circuit 34, and the output of the AND circuit 34 is sent to the latch memory. 36 data inputs. Also, bit 7 and bit 8 of the counter 30
The outputs of both are supplied to the AND circuit 32, the output of the AND circuit 32 is supplied to the data input of the latch memory 35,
The vertical synchronization signal 12a supplied to the reset input of the counter 30 is supplied to the clock input of the latch memory 36 and the latch memory 35, and the vertical synchronization signal 12a is supplied to the clock input of the latch memory 36 and the latch memory 35.
Store the input data in the data input at the start edge of .

The outputs of the latch memories 35 and 36 are combined into a set and output as a mode discrimination signal 27a of the horizontal scanning frequency of the input video signal. The mode discrimination circuit 27
The output mode discrimination signal 27a is supplied to the read-only memory 25 for storing the character font, and the storage area for the character font consisting of 18 lines and the storage area for the character font consisting of 15 lines are identified.

The characters or symbols shown in FIG. 3A are displayed on-screen in each area of the read-only memory 25 identified by the mode discrimination signal 27a at the address specified by the same data output from the video memory 24. Data for a character font having an 18-line configuration as shown in the example and data for a character font having a 15-line configuration shown in FIG. 2(b) are stored in advance. The horizontal scanning frequency determined by the mode determination signal 27a is 15.75 kHz.
Then, the data of the 18-line character font is read out sequentially, and at the horizontal scanning frequency of 24.43kHz, the 18-line character font data is
Data on the same line of character font data with a 5-line configuration is read out twice and output as 30-line character font data.

The repeated reading of the same line data is carried out using the vertical synchronizing signal 12 at the stage before the vertical character position counter 22.
By increasing the number of stages of the binary counter that counts b by one stage, the change period of the address signal for selecting data in units of scanning lines in the read-only memory 25 is reduced to 1/2. In addition, in the mode with the horizontal scanning frequency of 24.43 kHz, in the example of the mode discrimination circuit 27, all mode discrimination signals 27a are in a non-signal state, and the horizontal scanning frequency of 24.43 kHz is
．． In the same manner as in the 43 kHz mode, character font data of 18 lines is repeatedly read out twice for each line data.

[0018]

As described above, in a video display device that displays video signals in a plurality of horizontal scanning frequency modes including horizontal scanning frequency modes that are not related to double speed, on-screen display that is superimposed on the input video signal even when switching to each mode is provided. Characters and symbols can be displayed without changing their sizes. Moreover, the display control section can be easily integrated into an integrated circuit, and can be realized without adding any extra circuit parts, so that there is no increase in cost.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a display control unit for on-screen display according to the present invention.

FIG. 2 is a circuit diagram of a horizontal scanning frequency mode discrimination circuit.

FIG. 3 is a configuration diagram of a character font of the present invention.

FIG. 4 is a block diagram of a video display device.

[Explanation of symbols]

10 Input terminal 11 Signal synthesis section 12 Synchronization separation section 13 Display control section 13a Display signal 14 Control section 15 Key input section 24 Video memory 25 Read-only memory 27 Mode discrimination circuit 27a Mode discrimination signal 30 Counter 31 Decoder 34 Latch memory 35 Latch memory

Claims (1)

[Claims] Claim 1: Displaying video signals in multiple modes with different horizontal scanning frequencies, and storing character or symbol data in a video memory corresponding to a position on the display screen in synchronization with a synchronization signal separated from the video signal. In an on-screen display circuit that sequentially reads out character fonts, converts the same data into a display signal via a read-only memory that stores character fonts, and displays the same data superimposed on the same video signal, the read-only memory is divided into two, and the read-only memory is divided into two. Character font data consisting of 18 scanning lines is stored in advance in one area of the same address specified by the output data, and character font data consisting of 15 scanning lines is stored in the other area, and the synchronization signal is counted and the data is stored within one vertical scanning period. Based on the mode discrimination signal determined from the number of horizontal scanning lines, character font data consisting of 18 scanning lines is read in the mode with a horizontal scanning frequency of 15.75kHz, and character font data with 18 scanning lines is read out in the modes of 24.43kHz and 31.5kHz, respectively. 1. An on-screen display circuit for a video display device, characterized in that data of the same scanning line of a character font having a 15-scanning line configuration and a character font having an 18-scanning line configuration is repeatedly read out twice and outputted as a display signal.