JPH0727355B2 - Horizontal frequency switching circuit - Google Patents

Description

The present invention relates to a horizontal frequency switching circuit suitable for application to a signal supply device such as a personal computer capable of varying the horizontal resolution.

"Prior art" Normally, a personal computer (hereinafter referred to as a personal computer)
In such cases, the signal-processed data is supplied to the CRT and displayed on the CRT screen.

In recent years, there has been proposed a personal computer that improves the resolution of an image by varying the horizontal frequency when the image signal is processed.

When a high-resolution image signal is supplied to the CRT from the personal computer side, the horizontal frequency of the CRT is set to maintain the resolution by changing the horizontal frequency of the supplied image signal (from the horizontal frequency when obtaining normal resolution). Must also be switched to match.

For that purpose, it is necessary to detect the difference in horizontal frequency of the signals supplied from the personal computer side.

Conventionally, the number of pulses of the horizontal synchronizing signal in one vertical period of the image signal supplied on the CRT side is counted and determined. Alternatively, the horizontal synchronizing signal is frequency / voltage converted using a multivibrator for determination.

"Problem to be Solved by the Invention" By the way, as described above, if the horizontal frequency on the CRT side is switched by counting the number of pulses of the horizontal synchronizing signal, it takes time until the frequency switching signal is output. There is.

Further, when the discrimination is made by using the multivibrator, the signal is once converted into analog, so that an integrator, a comparator and the like are required to obtain the frequency switching signal, and there is a problem that the circuit becomes complicated.

Therefore, in the present invention, such a conventional problem is simply solved, and by adding information for discriminating the horizontal frequency to the signal generated on the signal supply device side, the horizontal on the CRT side is added. The present invention proposes a horizontal frequency switching circuit capable of easily and surely detecting a frequency.

[Means for Solving the Problems] In order to solve the above-mentioned problems, in the present invention, in a signal supply device capable of varying the horizontal frequency, the pulse width of the horizontal or vertical synchronization signal is based on the horizontal frequency selection mode. It is characterized by comprising a variable pulse width variable circuit and a switching means for switching the pulse width of the variable pulse width circuit according to a horizontal frequency selection mode.

[Operation] In the horizontal frequency switching circuit having such a configuration, as shown in FIG. 1, in the signal supply device (personal computer) 10,
A desired horizontal resolution is selected, and the switching means 14 is switched according to this selection mode.

Next, the pulse width varying circuit 12 varies the pulse width of the horizontal or vertical synchronizing signal according to the selected horizontal resolution.

As a result, the horizontal or vertical sync signal output from the signal supply device 10 includes information for determining the horizontal frequency.

Therefore, on the display means (CRT) 20 side, the horizontal frequency can be easily detected from the supplied signal in real time with a simple circuit configuration.

[Embodiment] Next, an example of the horizontal frequency switching circuit according to the present invention will be described in detail with reference to FIG.

FIG. 1 is a diagram showing a personal computer having a horizontal frequency switching circuit according to the present invention and a CRT having a detecting means for detecting a horizontal frequency from a signal supplied from the personal computer, and FIG. 2 is a timing chart of each signal.

As shown in FIG. 1, the personal computer 10 generates a horizontal synchronizing signal a (FIG. 2A) as the horizontal frequency switching circuit 1.
CRT controller 11, first monostable multivibrator 12 which is a pulse width variable circuit for varying the pulse width of the horizontal synchronizing signal a by the resistor R1 and the capacitors C1 and C2, and operates when the horizontal resolution is selected. A mode selection circuit 13 that outputs a mode selection signal m in accordance with the mode, and a switching unit 14 that switches in accordance with the mode selection signal m are provided.

On the other hand, the CRT 20 has a second monostable multivibrator 21 that outputs a signal e (FIG. 2D) having a preset pulse width Z, and a signal e that is output from the second monostable multivibrator 21. Pulse signal generating means 22 for generating a pulse signal P (E in the figure) which rises at the falling timing of
And the signal t supplied from the personal computer 10 is used as data, and the pulse signal P is used as a clock for the horizontal frequency switching signal b.
There is provided a detecting means 2 composed of a D-type flip-flop 23 for outputting and a third monostable multivibrator 24 for reproducing the synchronizing signal.

In the horizontal frequency switching circuit 1 having such a configuration, first, the horizontal resolution on the personal computer 10 side is the operation key (not shown).
Selected by. A mode selection signal m is output from the mode selection circuit 13 in accordance with this selection mode.

Depending on the mode selection signal m, the switching means 14 is A or B.
Switched to the side. As a result, the pulse width of the first monostable multivibrator 12 is determined by the resistor R and the capacitor C1 or C2.

The horizontal synchronizing signal a generated from the CRT controller 11 as shown in FIG. 2A is the first monostable multivibrator.
The pulse width corresponding to the selected mode is changed by 12.

For example, when the switching means 14 is switched to the A side for normal horizontal resolution, it is changed to a synchronizing signal having a pulse width X determined by the resistor R and the capacitor C1 as shown in FIG. 2B. It

Further, when changing to a higher horizontal resolution than usual, the switching means 14 is switched to the B side. At this time, the second
As shown in FIG. C, a synchronizing signal having a pulse width Y (Y> X) set by the resistor R and the capacitor C2 is output.

The synchronization signal t whose pulse width has been changed in this way is sent to a personal computer.
Supplied to CRT20 from 10.

The second monostable multivibrator 21 rises in synchronization with the supplied synchronization signal t and outputs a signal e having a pulse width Z preset by the resistor R2 and the capacitor C3 (see FIG. 2D). .

This pulse width Z is set to an intermediate pulse width between the pulse width X and the pulse width Y of the synchronizing signal t output from the first monostable multivibrator 12.

The signal e output from the second monostable multivibrator 21 is supplied to the pulse signal generating means 22. The pulse signal generating means 22 generates the pulse signal P as described above,
Output to the clock terminal of the D flip-flop 23.

As a result, in order to obtain a normal horizontal resolution, the synchronization signal t as shown in FIG.
Is supplied to the D flip-flop 23, the output Q of the D flip-flop 23, that is, the frequency switching signal b becomes a low level signal (second
(See Figure F).

On the other hand, in order to obtain a high horizontal resolution, when the synchronizing signal t as shown in FIG. 2C is supplied to the D flip-flop, its output Q becomes high level (see FIG. 2G).

Therefore, different frequency switching signals b can be obtained according to the pulse width of the synchronizing signal t supplied from the personal computer 10.

When a horizontal frequency oscillator (not shown) of the CRT 20 is driven based on the frequency switching signal b thus obtained, an image scanned with a horizontal frequency that matches the horizontal frequency of the image signal supplied from the personal computer 10. Is displayed on the CRT20.

Since the pulse width of the synchronizing signal t supplied from the personal computer 10 is changed in this way, it cannot be used as it is as a synchronizing signal.

Therefore, the third monostable multivibrator 24 generates a signal having the same pulse width as the pulse width T of the synchronization signal a (see FIG. 2A) output from the CRT controller 11 by using the resistor R3 and the capacitor C4. , The sync signal a is being reproduced (H in the same figure).

Therefore, the horizontal frequency of the signal supplied from the personal computer 10 can be easily and reliably detected without affecting other circuits that use the synchronization signal.

In this embodiment, a personal computer is used as the signal supply device and a CRT is used as the display means, but the present invention is not limited to this.

The configuration of the horizontal frequency switching circuit in this example is merely an example, and the present invention is not limited to this.

Although the pulse width of the horizontal synchronizing signal is changed in the above description, the pulse width of the vertical synchronizing signal can be changed to detect the horizontal frequency.

[Advantages of the Invention] As described above, according to the present invention, in the signal supply device capable of changing the horizontal frequency, the pulse width of the horizontal or vertical synchronizing signal of the signal supply device is changed according to the horizontal frequency. It is characterized by doing so.

Therefore, by adding information for detecting the horizontal frequency to the horizontal or vertical synchronizing signal supplied from the signal supply device, the horizontal frequency can be easily detected in real time on the display means side.

On the display means side such as a CRT, the horizontal frequency of the supplied signal can be detected easily and reliably by the detection means having a simple structure.

Further, the horizontal frequency can be switched on the display means side promptly.

Therefore, the horizontal frequency switching circuit according to the present invention is very suitable when applied to the personal computer as described above.

[Brief description of drawings]

FIG. 1 is a diagram showing a circuit configuration of a horizontal frequency switching circuit according to the present invention, and FIG. 2 is a timing chart of each signal of the horizontal frequency switching circuit according to the present invention. 1 ... Horizontal frequency switching circuit 2 ... Detection means 10 ... Signal supply device 12 ... Pulse width variable circuit 14 ... Switching means 20 ... Display means

Claims (1)

[Claims] 1. A signal supply device capable of varying a horizontal frequency, wherein a pulse width varying circuit for varying a pulse width of a horizontal or vertical synchronizing signal based on a horizontal frequency selection mode, and a pulse width of the pulse width varying circuit is horizontal. A horizontal frequency switching circuit comprising switching means for switching in accordance with a frequency selection mode.