JPS5990469A - Synchronizing control signal generating circuit for crt display - Google Patents

Abstract

PURPOSE:To obtain a horizontal and vertical control signal stable independently of the intensity of a received radio wave by utilizing a horizontal and a vertical blanking signal in a receiver. CONSTITUTION:The horizontal blanking signal is extracted as a horizontal synchronizing control signal from an output terminal 343. The vertical blanking signal is shaped a waveform into a pulse as shown in Fig. (c) by a waveform shaping circuit 347 and triggers a counter 349. When the counter 349 is reset, its output goes to ''L'' as shown in Fig. (d). A level ''H'' is introduced on an output terminal 344 as shown in Fig. (e). This ''H'' output is fed back to a gate 348, the horizontal blanking signal after waveform shaping is applied sequentially to the counter 349, and when the 9th pulse is counted, its output changes to ''H'', and the output of the inverter 350 is transferred to ''L''. Then, the vertical synchronism control signal in synchronizing with the vertical blanking signal and having a pulse width of the 8 horizontal blanking pulses' share is introduced from the terminal 344 as shown in Fig. (e).

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention connects a personal computer to a television receiver, and displays data images from the personal computer simultaneously on a CRT screen by superimposing them on a television broadcast image. The present invention relates to a synchronous control signal generation circuit for a CRT display capable of displaying images.

Recently, personal computers have generally come to be used at home. Attempts are now being made to connect a home color television receiver to a personal computer as a CRT display and display data from the personal computer on the color television receiver.

<Prior Art> FIG. 1 is a schematic diagram of a general CRT display showing a state in which a personal computer is connected to a color television receiver. First, with reference to Figure 1, the keyboard/
When the data inputted from is inputted into the personal computer, the data, -0, is displayed on the color television receiver 3.

R, G, 73 signals are included in the television circuit 3/ signal mixing circuit 3. ．． given to 2. And signal mixing circuit 3. ．． 2, R, G, and B signals are applied to the CRT 33, and characters or graphs are displayed.

By configuring the CRT display in this way, data images such as various characters and graphs can be displayed using the color television receiver 3 as a monitor. Recently, CRT displays have been devised that display data from a personal computer superimposed on a color television broadcast screen.

In this case, horizontal and vertical synchronization control signals are given to the personal computer from the synchronization control signal generating circuit 3 in the television circuit 3/ to synchronize the personal computer and the color television receiver 3.

Problems> By the way, in such a case, the personal computer J is normally provided with a Suito synchronization signal and a vertical synchronization signal obtained within the receiver as synchronization control signals. Fortunately, the size and pulse width of these horizontal and vertical synchronization signals change depending on the electric field strength of the television broadcast radio waves, and when the electric field strength is particularly weak, they are easily affected by noise, and may be affected by spurious synchronization signals. There was a risk that the synchronization operation of the personal computer would be disrupted.

<Purpose> Unexploded 11J-7 was designed in consideration of these points, and uses the horizontal and vertical blanking signals in the receiver to generate stable horizontal and vertical synchronization control signals regardless of the strength of the received radio waves. The present invention provides a synchronous control signal generation circuit that can obtain the following.

<Example> The present invention will be described below according to an example shown in FIG. FIG. 2 shows a block diagram of an embodiment of the present invention, in which the synchronous control signal generation circuit is a waveform shaping circuit 34t6.
．． 3gt, 3g2, Antoge-1tomi) 5.3g♂, Bc
It consists of a D♂ base kakunta 3g 2, and an in□゛2 (bark 360), one input terminal 3g/ is supplied with a horizontal blanking signal as shown in Fig. 3(a), and the other Figure 3 (bJ
A vertical blanking signal as shown in FIG.

The horizontal blanking signal is passed through the waveform shaping circuit 3'1.5, shaped into a waveform, and taken out from the output terminal 3 as a horizontal synchronization control signal, and this horizontal blanking signal is passed through the waveform shaping circuit 341t. After waveform shaping, AND gate, 34'l? is input. On the other hand, the vertical planking signal is waveform-shaped through the waveform shaping circuit 37 into a pulse as shown in FIG. 3(c), and this pulse is applied as a trigger pulse to the BCD♂ advance counter 34t2.

The counter 32 is reset by this trigger pulse, and the output of the counter 32 is as shown in FIG. 3(d).
It becomes IILll. At this time, as shown in FIG. 3 (el), II HI
An output I is derived. This °'H” output is
During this time, since the AND gate 3g is open, the horizontal blanking signal after waveform shaping is sequentially supplied to the BCD♂ advance counter 3g 2. This counter 3g2 performs a counting operation, and when the second horizontal blanking signal is counted, its output changes from 11 L 11 to 'H', and accordingly, the output of In and Bark 35θ becomes °'H
” to L2”. As a result, the AND gate 3g♂ is thereafter closed, and the counter 34t2 is supplied with the next vertical blanking signal to the input terminal 3g, and its counting operation is stopped until it is reset by the trigger pulse.

Every time a vertical blanking signal is supplied from such a result output terminal 3, as shown in Figure 3 (el), it synchronizes with the blanking signal and calculates the pulse width of r horizontal blanking signals. A vertical synchronization control signal having a vertical synchronization control signal is derived.

<Effects> As described above, according to the present invention, a personal computer is connected to a television receiver, and a data image from the personal computer can be simultaneously projected and displayed by superimposing the television broadcast image on the CRT screen. Based on the display number, a horizontal synchronization control signal for personal computer synchronization is obtained based on the V-blanking signal in the receiver, and a horizontal synchronization control signal for personal computer synchronization is obtained based on the horizontal blanking signal and vertical blanking signal. Since the vertical control signal is obtained, a stable synchronization control signal with a constant pulse width can be obtained without being affected by the strength of received radio waves or noise.

Therefore, if the personal computer is synchronized using the synchronization control signal obtained by the circuit of the present invention, there will be no malfunction, and a stable image in which the broadcast image and the data image are superimposed will be displayed on the CRT screen-4. Is displayed.

[Brief explanation of drawings]

Fig. 1 is a diagram of a CRT display in which a general personal computer is connected to a color television receiver, and Fig. 2 is a block diagram of an embodiment of the synchronous control signal generation circuit of the present invention. FIG. 3 is an input/output signal waveform diagram of each part in the same embodiment. 2...Personal computer, 3...Color television receiver, 33...CRT, , 3'l.
...Synchronous control signal generation circuit, 3-ctor...B
C0g hex counter.

Claims (1)

[Claims] 1. In a CRT display where a personal computer is connected to a television receiver and data images from the personal computer can be simultaneously displayed on the CR1 screen by superimposing them on television broadcast images, means for obtaining a horizontal synchronization control signal for personal computer synchronization, and a means for counting a predetermined number of horizontal blanking signals using a vertical blanking signal in the receiver as one signal to start counting, and for vertical synchronization for personal computer synchronization. A synchronous control signal generation circuit for a CRT display, comprising means for obtaining a control signal.