JPH06189196A - On-screen display device - Google Patents

Abstract

(57) [Abstract] [Purpose] To enable on-screen display of a multi-scan monitor using video signals with different horizontal frequencies as input sources. [Structure] A means for generating a dot clock signal S7 corresponding to the frequency of the horizontal synchronizing signal S1, and a character to be displayed on the cathode-ray tube based on the horizontal synchronizing signal S1, the vertical synchronizing signal S2, the control signal S8 and the dot clock signal S7. The display control unit 5 for controlling the display timing, the memory unit 6 for outputting a required character code under the control of the display control unit 5, etc., and the memory unit 6 for outputting the raster address control signal S11 from the display control unit 5 A character generator 7 that outputs a character pattern signal corresponding to a character code, a converter 8 that converts parallel data output from the character generator 7 into serial data, and a switching circuit that superimposes an on-screen display signal S13 on a video signal S3. 9 and a control unit 2 for controlling generation of the dot clock signal S6 and the like.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an on-screen display of a multi-scan monitor using video signals having different horizontal frequencies as input sources.

[0002]

2. Description of the Related Art Conventional on-screen display is possible under the condition that the horizontal frequency is constant. Therefore, in the case of the multi-scan monitor whose horizontal frequency changes depending on the input video signal, it is difficult to perform correct on-screen display corresponding to all the horizontal frequencies. Further, since the dot clock of the on-screen circuit is constant, the number of displayed characters and the size of the characters also change when the horizontal frequency changes.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an on-screen display device capable of following a horizontal frequency change of an input video signal in order to enable on-screen display on the multi-scan monitor. And

[0004]

According to the present invention, there is provided means for generating a dot clock signal corresponding to the frequency of an input horizontal synchronizing signal, the input horizontal synchronizing signal, vertical synchronizing signal, and control by a controller. A display control unit that controls the display timing of the characters displayed on the cathode-ray tube based on the signal and the dot clock signal, and the character code to be displayed is stored in advance, and the required control is performed based on the control by the control unit and the display control unit. A memory unit that outputs a character code, a character generator that outputs a character pattern signal corresponding to the character code from the memory unit based on a raster address control signal from the display control unit, and parallel data output from the character generator. Is converted to serial data and converted to an on-screen display signal in parallel /
A serial converter, a switching circuit for switching between an input video signal and the on-screen display signal and superimposing the on-screen display signal on the video signal, generation of the dot clock signal, control of a display control unit and a memory unit The present invention provides an on-screen display device configured with a control unit that operates.

[0005]

[Function] Counts the horizontal synchronizing signal with the frequency counter,
The control unit detects how many times (probably N times) the horizontal frequency as a reference, and controls the oscillator based on the detection result to oscillate a signal having a frequency N times the reference oscillation frequency. . The oscillated signal, which is more accurate and stabilized in frequency, is used as a dot clock signal to generate required character data by the display control unit, the memory unit, the character generator, and the like. Character data from the charactor generator is rearranged from parallel to serial and is superimposed on a video signal so as to follow scanning.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An on-screen display device according to the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of essential parts showing an embodiment of an on-screen display device according to the present invention. In FIG. 1, S1 is a horizontal sync signal (HD) separated from the input video signal, S2 is the same vertical sync signal (VD), 1 is a frequency counter for counting the horizontal frequency from the horizontal sync signal, 2 is a control unit, 3 Is an oscillator that oscillates a dot clock signal of a required frequency under the control of the control unit 2, and 4 is an oscillator 3.
For accurately synchronizing the dot clock signal from the above with a horizontal synchronizing signal and making it a stabilized dot clock signal.
The L circuits and 5 are display control units (CRTC) for controlling the memory unit 6 and the character generator 7 to output required character data based on the dot clock signal from the PLL circuit 4 and the control of the control unit 2, and the like. A memory unit that stores a character code, 7 is a character generator that outputs a character pattern signal corresponding to the character code from the memory unit 6, and 8 is data that is output in parallel from the character generator 7 and that is converted into serial data. The parallel / serial converter 9 is a switching circuit for superimposing the character signal from the parallel / serial converter 8 on the video signal S3.

Next, the operation of the present invention will be described. A feature of the present invention is that each time the horizontal frequency of the input video signal changes, a dot clock signal adapted to the horizontal frequency is generated. The dot clock signal is a clock signal that serves as a reference when reading a character signal composed of dots. Therefore, the frequency of the horizontal synchronizing signal is measured (counted) by the frequency counter 1, and the frequency count data S4 is sent to the control unit 2. The control unit 2 calculates, based on the frequency count data S4, how many times the horizontal frequency of the input signal is a value held by the control unit 2 as the reference horizontal frequency data. Let this be N times. The control unit 2 outputs the oscillation control signal S5 according to the calculated value, and controls the oscillation frequency of the oscillator 3 to be N times the value that the control unit 2 has as the reference dot clock data.

In this way, the dot clock signal S6 is output from the oscillator 3, and the dot clock signal S6 is PLL.
The circuit 4 produces a dot clock signal S7 that is accurately and stably synchronized with the horizontal synchronizing signal S1. The display control unit 5 for controlling the display timing on the cathode ray tube (CRT) includes the dot clock signal S7, the control signal S8 from the control unit 2 to the display control unit 5, the horizontal synchronizing signal S1 and the vertical synchronizing signal.
The required character code S10 is read from the memory section 6 by the memory address control signal S9 based on S2. The character code
The character generator 7 to which S10 is input outputs the character pattern signal S12 corresponding to the character code S10 to the display controller 5
Output by the raster address control signal S11. Here, the specific contents of the character code S10 read from the memory unit 6 and the horizontal display position of the screen are determined by the memory address control signal S9. The vertical display position of the screen is determined by the raster address control signal S11 for the character generator 7. Then, the horizontal synchronization signal S1 and the vertical synchronization signal S2 are the basis for determining the display position.
Is.

The character pattern signal S12 output from the character generator 7 is a parallel output in which the data forming each character is output at the same time. Even if this output signal is scanned, the character will not be a normal character, so the serial data array is formed. I have to convert. Parallel / serial converter 8
Is provided for this conversion. The dot clock signal S7 is used for this conversion, and the converted signal is the final on-screen display signal S13. The on-screen display signal S13 is sent to the switching circuit 9 by the switching signal S1.
It is switched to the video signal S3 by 4 and inserted at a predetermined position. As a result, the predetermined character signal is superimposed on the predetermined position of the video signal. The character superposition position is determined by the switching timing of the switching signal S14.

[0010]

As described above, according to the present invention, the dot clock signal indispensable for on-screen display is a clock signal having a frequency that matches the horizontal frequency of the input video signal. Therefore, at any horizontal frequency. On-screen display in which the number of horizontally displayed characters and the size of the characters are the same is possible, which largely contributes to the improvement of the function of the multi-scan monitor using video signals having different horizontal frequencies as input sources.

[Brief description of drawings]

FIG. 1 is a block diagram of essential parts showing an embodiment of an on-screen display device according to the present invention.

[Explanation of symbols]

 1 Frequency Counter 2 Control Unit 3 Oscillator 4 PLL Circuit 5 Display Control Unit (CRTC) 6 Memory Unit 7 Character Generator 8 Parallel / Serial Converter 9 Switching Circuit

Claims (2)

[Claims] 1. A means for generating a dot clock signal corresponding to a frequency of an input horizontal synchronizing signal, and the input horizontal synchronizing signal, vertical synchronizing signal, a control signal from a control unit and the dot clock signal. A display control unit for controlling the display timing of the characters to be displayed on the cathode-ray tube based on the display, and a memory unit for storing the character code to be displayed in advance and outputting a required character code based on the control by the control unit and the display control unit. A character generator that outputs a character pattern signal corresponding to a character code from the memory unit based on a raster address control signal from the display control unit; and parallel data output from the character generator is converted into serial data and turned on. Parallel / serial converter for screen display signal, input video signal and ounce A switching circuit for switching a clean display signal and superimposing the on-screen display signal on the video signal; and a control unit for controlling the generation of the dot clock signal, the display control unit and the memory unit. On-screen display device. 2. The dot clock signal generating means includes a frequency counter for counting the frequency of the input horizontal synchronizing signal, an oscillator for generating a required dot clock signal under the control of a control unit, and the counted frequency. Of the reference horizontal frequency data, and a control unit for controlling the oscillator so that the frequency of the reference dot clock signal corresponding to the reference horizontal frequency data becomes the multiple, and a dot clock signal from the oscillator. And a PLL circuit for converting the dot clock signal in synchronization with the horizontal synchronizing signal into a PLL circuit.
The on-screen display device described.