JP2745540B2 - Teletext receiver - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a teletext receiver for receiving a television multiplex teletext signal and displaying a text screen.

2. Description of the Related Art In recent years, a text multiplex broadcasting service has been started in which a text signal is multiplexed and broadcast in several horizontal periods within a vertical retrace period of television broadcasting.

In the text multiplex broadcasting, there are programs such as a subtitle program and a one-line horizontal scrolling program that display character information superimposed on a television image. In addition to such programs, there are also programs in which only character / graphic information is fixedly displayed on the entire surface. In the case of full-screen fixed display, flicker occurs due to interlaced scanning when display is performed in accordance with the television's original synchronization signal, and the display screen is difficult to see. Therefore, when not superimposed on a television picture, a method of generating a synchronizing signal that does not cause interlaced scanning and displaying character / graphic information according to the synchronizing signal is adopted.

Some broadcasting stations do not provide teletext broadcasting services. To determine whether teletext is multiplexed on a selected television signal, the presence or absence of teletext is determined by extracting the multiplexed horizontal period.

When a teletext program is viewed, the operation is performed by operating a key called teletext provided on an input keypad or the like, and the character / graphic information is decoded and displayed by operating the key.

In order to decode and display the character / graphic information, it takes some time to determine whether or not the character signal has been extracted or not, and a means for displaying an initial screen when the selected channel is changed is used. After the initial screen is displayed, when the teletext service is not being performed, a message of "no teletext" is displayed to inform the viewer of the fact. As a display of these messages, a teletext receiver for superimposing and displaying text information on a television image has been put to practical use. In such a teletext receiver, a display clock for presenting a teletext, a horizontal synchronizing signal, and a vertical synchronizing signal are switched between when the teletext is superimposed on the television broadcast and when the teletext is not superimposed. .

In the following, referring to the drawings, the character graphic information is superimposed on the television image of the teletext receiver described above (hereinafter referred to as superimpose), and the character graphic information is displayed independently (hereinafter referred to as full-screen fixed display). A description will be given of the synchronization signal and the switching control of the display clock.

In FIG. 3, 1 is a crystal oscillator, 2 is an internal clock generation circuit for generating a display clock using the crystal oscillator,
3 is a horizontal synchronizing signal phase-synchronized with the clock ICLK generated by the internal clock generating circuit based on the clock ICLK.
This is an internal synchronization generation circuit that generates an IHD and a vertical synchronization signal IVD. Reference numeral 4 denotes a video signal input to A, which is separated in synchronization, a horizontal synchronization signal is output as an external horizontal synchronization signal EHD controlled by a phase synchronization circuit, and a vertical synchronization signal is an external vertical synchronization signal EVD which is still separated in synchronization. This is a synchronization separation circuit. 5 is a gated oscillator for generating a display clock ECLK synchronized with the external horizontal synchronizing signal EHD, 6 is a switching circuit for switching between a display clock and horizontal and vertical synchronizing signals, and 7 is a register for controlling the switching of the switching circuit 6.

Hereinafter, the operation will be described. When the entire character / graphic information is fixedly displayed, "0" is written into the register 7 via the data line B and the register light panel C by a microprocessor (not shown) for decoding the character / graphic information, and the superimpose is performed. To do so, write "1" to register 7. When "1" is written to the register 7, ECLK, EHD, and EVD are selected as a display clock for decoding and displaying character / graphic information, a horizontal synchronizing signal, and a vertical synchronizing signal, respectively, and are output from the D, E, and F terminals. You. Since these ECLK, EHD, and EVD are all synchronized with the video signal input to A, character and graphic information can be displayed over the video signal. When "0" is written to the register 7, ICLK, IHD, and IVD are selected.

However, in the conventional teletext receiver as described above, when "1" is written to the register 7 for superimpose when a video signal is not input, decoding and display are performed. The display clock, horizontal sync signal and vertical sync signal are switched to ECLK, EHD and EVD created from the input video signal, but the screen flows because there is no video signal,
The message screen such as "There is no teletext" cannot be read, which has been a problem.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and to provide a teletext receiver capable of displaying a message without a message screen or the like even when a video signal is not input.

Means for Solving the Problems The teletext receiver of the present invention has a display clock and a horizontal synchronizing signal for presenting teletext when a teletext is superimposed on a television broadcast and when not displayed. As means for controlling the circuit for switching the vertical synchronization signal, a first counter for counting the vertical synchronization signal from the internal synchronization generation circuit, and a second counter for counting the vertical synchronization signal obtained by synchronizing and separating the video signal are provided. Resetting the first counter with the count output of the second counter, setting the set / reset circuit, and resetting the set / reset circuit with the count output of the first counter. The output of the register is controlled when the selection of superimpose or full-screen display is selected by the output of the reset circuit. You.

Operation According to the present invention, when a video signal is not input, the present invention does not switch to the ECLK, EHD, and EVD generated from the video signal. This prevents the display of the character / graphic information from flowing and being unreadable.

Embodiment Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a configuration of a switching portion between a display clock and a synchronization signal of a teletext receiver according to the present invention. 1 is a crystal oscillator, 2 is an internal clock generation circuit, 3 is an internal synchronization generation circuit, 4 is a synchronization separation circuit, 5 is a gated oscillator, 6 is a switching circuit, and 7 is a register. These are the same as those of the conventional example. Reference numeral 8 denotes a first counter for counting the vertical synchronization signal generated by the internal synchronization generation circuit 3, and reference numeral 9 denotes a second counter for counting the vertical synchronization signal synchronized and separated by the synchronization separation circuit 4.
It is a counter of. Reference numeral 10 denotes an OR circuit, to which a channel switching pulse H indicating that channel switching has been performed and the count output RC2 of the second counter 9 are input, and the output is input to the reset terminal of the first counter 8. The channel switching pulse H is also input to the reset terminal of the second counter. A set / reset circuit 11 has a reset input terminal connected to the count output RC1 of the first counter, and a set input terminal connected to the count output RC2 of the second counter. Reference numeral 12 denotes an AND circuit, to which the output of the set / reset circuit 11 and the output of the register 7 are inputted,
Is connected to the switching control terminal of

Next, the operation will be described. The first counter counts twice as much as the second counter. When the selected channel is switched, a channel switching pulse H is input,
The first counter 8 and the second counter 9 are reset.
When the selected channel is not an empty channel, a video signal exists, and the vertical synchronization signal separated by the synchronization separation circuit 4 is input to the second counter 9, and when 15 signals are input, a count output RC2 is output. , Reset the first counter. RC2 sets the set / reset circuit 11, and its output Q becomes "1". The vertical synchronization signal generated by the internal synchronization generation circuit 3 is input to the first counter. However, since the count value is twice 30, RC1 is not output, and the output Q of the set / reset circuit is “ 1 "remains. This state is shown in FIG.

Therefore, when superimposing according to the contents written in the register 7, the character / graphic information is decoded and superimposed and displayed on the video image based on the display clock and the synchronizing signal synchronized with the video signal. .

If the selected channel is an empty channel,
Since the video signal is not input, the count output RC2 is not output from the second counter. At this time, the internal vertical synchronizing signal is always output.
When the number is input, the count output RC1 is output from the first counter, the set reset circuit 11 is reset, the output Q becomes "0", and the output of the AND circuit 12 becomes "0" regardless of the contents of the register 7. As a result, the message is always displayed by the internal clock and the internal synchronization signal, and the message is displayed in a legible manner so that the message does not flow. This state is shown in FIG. 2b.

As described above, in the teletext receiver according to the present invention, the first counter that counts the vertical synchronization signal from the internal synchronization generation circuit counts the vertical synchronization signal obtained by synchronizing and separating the video signal. A reset circuit that resets with a count output of the second counter and controls an output of a register that performs switching selection between superimposition and full-screen display is reset with the count output of the first counter. When no video signal is input, superimposition does not occur, so message screens such as "No teletext" do not appear without a sync signal and are displayed well. Also, when a video signal is input, the character / graphic screen is displayed in superimpose according to the register, and the internal synchronization signal is generated. It is possible to perform a fixed display without flickering in accordance with the synchronization signal of the livestock.

[Brief description of the drawings]

FIG. 1 is a block diagram of a teletext receiver according to one embodiment of the present invention, FIG. 2 is a timing chart showing the operation of the circuit,
FIG. 3 is a block diagram of a conventional teletext receiver. 2 ... internal clock generation circuit, 3 ... internal synchronization generation circuit, 4 ... synchronization separation circuit, 5 ... gated oscillator, 6
... Switching circuit, 7... Superimpose, full-screen fixed display designation register, 8... First counter, 9... Second counter, 11.

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Toyoaki Unemura 1006 Kazuma Kadoma, Kadoma City, Osaka Inside Matsushita Electric Industrial Co., Ltd.

Claims (1)

(57) [Claims] 1. A switching means for switching between a display clock and a horizontal synchronizing signal and a vertical synchronizing signal when a text broadcast is superimposed on a television broadcast and not superimposed, and an output of a register for switching and selecting the switching means. A reset signal that outputs a pulse signal that controls the internal clock signal, an internal clock generator that generates a display clock that does not maintain the phase relationship with the input video signal, and an internal synchronization signal that is generated based on the display clock. A synchronizing / separating circuit having a horizontal oscillating circuit for phase-synchronizing a horizontal synchronizing signal synchronized with an input video signal, a gated oscillator for generating a display clock synchronized with the horizontal oscillating circuit, The internal vertical synchronizing signal reset by a pulse and output from the internal synchronizing signal generation circuit is counted and counted m times. That the counting of the first counter and is reset by the channel switching pulse sync separated vertical synchronizing signal by the synchronous separation circuit for outputting a first signal for resetting the set reset circuit, m>
a second counter that outputs a second signal that sets the set / reset circuit when counting is performed n times with an integer n of n. The count output of the second counter is controlled by the count output of the second counter. None, when there is a video signal input, the first counter is reset with the second signal and the set reset circuit is set to output a first switching signal. When there is no video signal input, the first switch is output. The set reset circuit is reset by a signal to output a second switching signal, and the switching means is operated by the first and second switching signals using the count outputs of the first and second counters. By controlling the switching, the display clock, the horizontal synchronization signal, and the vertical synchronization signal for presenting the teletext are displayed depending on whether the teletext is superimposed on the television broadcast or not. When the video signal is not input, the switching means is controlled by the second switching signal so that the selection of the display clock and the synchronization signal synchronized with the video signal is prohibited, and the video signal does not exist. A teletext receiver characterized in that the time is always displayed using an internal display clock and an internal synchronization signal.