JPS6353752B2 - - Google Patents

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. This relates to a synchronous control signal generation circuit for a CRT display.

Recently, personal computers have generally come to be used in homes. 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> Figure 1 shows a general technology in which a personal computer is connected to a color television receiver.
1 is a schematic diagram of a CRT display. First, referring to FIG. 1, when data entered from the keyboard 1 is inputted to the personal computer 2, R, G, and B signals for displaying the data on the color television receiver 3 are sent to the television circuit 31.
is applied to a signal mixing circuit 32 included in the signal mixing circuit 32 included in the signal mixing circuit 32 . Then, the R, G, and B signals are transmitted through the signal mixing circuit 32.
It is given to the CRT33 and characters or graphs are displayed.

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

In this case, horizontal and vertical synchronization control signals are provided to the personal computer 2 from the synchronization control signal generation circuit 34 in the television circuit 31 to synchronize the personal computer 2 and the color television receiver 3.

<Problems> In such a case, the personal computer 2 is normally given a horizontal synchronization signal and a vertical synchronization signal obtained within the receiver as synchronization control signals. However, 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 they are easily affected by noise especially when the electric field strength is weak, and pseudo synchronization signals may cause personal There was a risk that the synchronization operation of the computer 2 would be disturbed.

<Purpose> The present invention has been made in view of the above points, and it is an object of the present invention to obtain stable horizontal and vertical synchronization control signals regardless of the strength of received radio waves by using horizontal and vertical blanking signals in a receiver. The present invention provides a synchronous control signal generation circuit that can perform the following functions.

<Example> The present invention will be described below according to an example shown in the drawings. FIG. 2 shows a block diagram of an embodiment of the present invention, in which the synchronous control signal generation circuit is composed of waveform shaping circuits 345, 346, 347, an AND gate 348, a BCD octal counter 349, and an inverter 350; input terminal 341
A horizontal blanking signal as shown in FIG. 3a is supplied to the input terminal 342, and a vertical blanking signal as shown in FIG. 3b is supplied to the other input terminal 342.

The above horizontal blanking signal is generated by the waveform shaping circuit 34.
The horizontal blanking signal is passed through a waveform shaping circuit 346, shaped into a waveform, and taken out as a horizontal synchronization control signal from an output terminal 343.
is input. On the other hand, the vertical blanking signal is waveform-shaped through the waveform shaping circuit 347 into a pulse as shown in FIG. 3c, and this pulse is applied to the BCD octal counter 349 as a trigger pulse.
The counter 349 is reset by this trigger pulse, and the output of the counter 349 becomes "L" as shown in FIG. 3d. At this time, an "H" output is derived from the output terminal 344 via the inverter 350 as shown in FIG. 3e. This "H" output is fed back to the AND gate 348 as the other input, and since the AND gate 348 is open during this time, the horizontal blanking signal after waveform shaping is
The signals are sequentially supplied to the BCD octal counter 349. This counter 349 performs a counting operation, 9
When the horizontal blanking signal is counted, its output changes from "L" to "H", and accordingly, the output of the inverter 350 changes from "H" to "L". As a result, the AND gate 348 is thereafter closed, and the counter 349 stops its counting operation until the next vertical blanking signal is supplied to the input terminal 342 and is reset by the trigger pulse.

From such a result output terminal 344,
As shown in FIG. 2, each time a vertical blanking signal is supplied, a vertical synchronization control signal is derived which is synchronized with the blanking signal and has a pulse width of eight horizontal blanking signals.

<Effects> As described above, according to the present invention, a personal computer is connected to a television receiver, and data images from the personal computer can be simultaneously projected and displayed on the CRT screen by superimposing television broadcast images on the CRT display. , obtains a horizontal synchronization control signal for personal computer synchronization based on the horizontal blanking signal in the receiver, and obtains a vertical synchronization control signal for personal computer synchronization based on the horizontal blanking signal and vertical blanking signal. Therefore, 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 a 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 data image are superimposed will be displayed on the CRT screen. be done.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of a CRT display in which a general personal computer is connected to a color television receiver, Fig. 2 is a block diagram of an embodiment of the synchronous control signal generation circuit of the present invention, and Fig. 3 is the same embodiment. FIG. 2... Personal computer, 3... Color television receiver, 33... CRT, 34... Synchronous control signal generation circuit, 349... BCD octal counter.

Claims (1)

[Claims] 1. In a CRT display, in which a personal computer is connected to a television receiver, and data images from the personal computer can be simultaneously projected and displayed on the CRT screen by superimposing the television broadcast image, means for obtaining a horizontal synchronization control signal for personal computer synchronization, and a means for obtaining a horizontal synchronization control signal for personal computer synchronization by counting a predetermined number of horizontal blanking signals using a vertical blanking signal in a receiver as a trigger signal for starting counting. A CRT equipped with the means to obtain
Display synchronous control signal generation circuit.