JPH0260194B2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention enables automatic switching of the number of scanning lines between 400 lines and 200 lines in a CRT display device used for displaying electronic devices such as personal computers. related to things.

<Prior art> In recent years, the graphic functions of electronic computers such as personal computers have been improved to enable display of kanji characters, and many of these are 320 x 200 dots, 640 x 200 dots, or 640 x 200 dots.
The video output has a resolution of 640 x 400 dots.

CRT display devices that are compatible with this graphic display are 320 x 200 dots and 640 x 200 dots, and the number of scanning lines is less than the 230 scanning lines of commercially available television receivers. When used as a device, there are few improvements to be made, and especially for home use, it is often used also as a television receiver.

On the other hand, in a CRT display device that displays 640×400 dots, the number of scanning lines increases, so in principle it is necessary to lower the vertical deflection frequency. In practice, the vertical deflection frequency cannot be lowered too much to prevent cathode ray tube flickering, for example 50-55 for 60Hz for 200 lines.
It can only be lowered to about Hz. Therefore, it is necessary to increase the horizontal deflection frequency, which is about 22.73KHz compared to 15.75KHz for 200 lines. Therefore,
CRT display devices are often specialized because their vertical and horizontal deflection frequencies are significantly different from those of regular television receivers.

Therefore, such a 400-line receiver has little demand, especially for home use, and tends to be expensive.

<Objective> The present invention eliminates the above drawbacks and provides a CRT display device in which the number of scanning lines can be freely switched between 200 lines and 400 lines.

<Embodiment> Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the basic configuration for switching between 200 and 400 scanning lines. In the video signal V output from a certain personal computer 1, a discrimination pulse P for 400 line discrimination is weighted during the vertical blanking period R in the luminance signal component, as shown in FIG. 2b. This is input to the 400 line discrimination circuit 2, which detects the presence or absence of a pulse during the vertical blanking period, and if it is 400 lines, outputs the output signal C, and the DC conversion circuit 3 consisting of an integrating circuit outputs a predetermined signal. A level control voltage is delivered. As a result, the deflection coil impedance switching circuit 4 is activated by switching the transformer tap, the horizontal output line adjustment circuit 5 is activated by changing the resonance capacitance, the horizontal position correction circuit 6 is activated by changing the phase of the AFC pulse, and the vertical By operating the amplitude switching circuit 7 and the vertical synchronization switching circuit 8 by switching the synchronization volume constant, the number of scanning lines is switched from 200 line mode to 400 line mode, and the video signal is supplied to the CRT 10 through the video signal processing circuit 9. is displayed on the screen.

In addition, in the present invention, the number of horizontal scanning lines is 200 lines and 400 lines.
Although switching with the line has been shown, it is also possible to switch to even more deflection frequencies by increasing the number of discrimination pulses within the vertical blanking period, and it is also possible to easily cope with even higher resolution. It is possible.

<Effects> As described above, the CRT display device of the present invention detects the discrimination pulse indicating deflection frequency switching inserted during the blanking period in the video signal of a personal computer, and changes the deflection frequency accordingly. By automatically switching the CRT display device, even if the CRT display device does not have a changeover switch, it is automatically changed by the video output of the personal computer, improving operability and increasing the number of scanning lines from 200 lines to 400 lines. Since it can be used in various ways, it is possible to easily lower the price through mass production.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of a CRT display device of the present invention, and FIG. 2 is a waveform diagram of discrimination pulses detected by the display device.

Claims (1)

[Claims] 1. In a CRT display device in which the vertical and horizontal deflection frequencies can be switched and the screen resolution can be varied, an image output device that applies a discrimination pulse during the blanking period of the video signal according to the switching of the deflection frequency. means for detecting a discrimination pulse in the output of a video signal; and means for switching to a mode corresponding to the deflection frequency based on the detection output.
CRT display device.