JPH04361487A - Video signal automatic changeover circuit - Google Patents

Abstract

PURPOSE:To observe a video signal not scrambled even when a power supply for a decoder is interrupted by detecting the presence of a period signal of a video output of a decoder connecting to a re-input terminal so as to select the input of the video signal. CONSTITUTION:A video signal received by a BS tuner is given to a switch 10. Simultaneously, a bit stream output and an AFC detection output are given to an external scramble decoder 9. The video output of the decoder descrambled is given to a synchronizing signal detection circuit 8 via a re-input terminal 16. When the detection circuit 8 detects a synchronizing signal, an interface circuit 12 selects a video signal changeover circuit 10 to an input terminal 14 at the decoder side.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic video signal switching circuit for video equipment equipped with an external video signal input terminal.

0002

BACKGROUND OF THE INVENTION In recent years, private satellite broadcasting has started, and satellite broadcasting has come to play a role as a new medium. Among these, paid broadcasting channels scramble the transmitted signals, so they cannot be viewed as is. Therefore, for example, in the case of a television receiver with a built-in BS tuner, the reception system is such that the signal once received is input to the television receiver again through a dedicated decoder. It became necessary to switch between the signal and the video signal descrambled by the decoder on the television receiver side.

Conventionally, in switching in this case, a device with a mechanical interlocking switch as shown in FIG. 2 is used as the re-input terminal of the scramble signal, and when the output of the decoder is connected to the re-input terminal, A switch was mechanically switched to the output side of the decoder to switch between an unscrambled normal video signal and a video signal descrambled by the decoder.

0004

[Problem to be solved by the invention] However, when switching is performed using such a mechanical interlocking switch,
When the decoder output is connected to the re-input terminal, only the decoder output signal is always input, so when the decoder is powered off, not only the unscrambled video signal but also the scrambled video signal is input. If you want to view unscrambled video signals, you will need to turn on the decoder or disconnect the decoder output from the re-input terminal. There was a problem that operations became complicated.

[0005]

[Means for Solving the Problems] In order to solve the above problems, the present invention detects the presence or absence of a synchronizing signal for the video output of a decoder connected to a re-input terminal, and switches the input of the video signal. That is.

[0006]

[Operation] According to the present invention, when there is a synchronizing signal at the video output of the decoder connected to the re-input terminal, that is, when there is a video signal, the video signal changeover switch is switched to the output side of the decoder, and the re-input terminal is switched to the output side of the decoder. If there is no synchronizing signal in the video output of the decoder connected to the terminal, that is, if there is no video signal, or if the decoder is powered off, the video signal changeover switch will automatically switch to the internal normal video signal side. You can switch to .

Furthermore, as claimed in claims 2 and 3, forcibly switching to the decoder side even when there is no video signal corresponds to the case where there is no video signal and only the audio signal is scrambled and broadcast. This is to do so.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a schematic diagram of an automatic video signal switching circuit according to an embodiment of the present invention.

In FIG. 1, 7 is a microcomputer, 8 is a synchronization signal detection circuit, 9 is an externally connected scramble decoder, 10 is a video signal changeover switch, 1
1 is a BS tuner, 12 is an interface circuit for 7, 8, and 10, and 21 is an audio signal changeover switch that is interlocked with the switch 10.

First, the video signal received by the BS tuner is connected as is to the input terminal 2 of the changeover switch 10. At the same time, the bit stream output and AFC detection output are connected to an external scramble decoder, and the video output of the decoder, which is descrambled there, is connected to the re-input terminal 16 on the video equipment side and connected to the synchronization signal detection circuit 8. , 10 are connected to the input terminal 1 (14) of the video signal changeover switch. At this time, 16
When there is a synchronization signal in the signal connected to the circuit, the output of the synchronization signal detection circuit 8 becomes a "LOW" state in binary logic, turning off the transistor 6 and causing the output of the interface circuit 12 to become a "HIGH" state. , 10 are switched to the input terminal 1 side (14). vice versa,
If there is no synchronization signal in the signal connected to 16, the output of the synchronous signal detection circuit 8 will be in the "HIGH" state in binary logic, turning on the transistor 6 and switching on the interface circuit 1.
The output of No. 2 is set to the "LOW" state, and the video signal changeover switch No. 10 is switched to the input terminal 2 side (15). At this time, the I/O port 13 of the microcomputer 7 is an input port and is in a high impedance state, so it does not affect the above switch operation.

Next, the I/O of the microcomputer 7
If the port is an output port, in other words, the 10 video signal changeover switches are forced to the input terminal 1 side (14
), I/O port 13 is set to “LOW”.
Regardless of the state of the output of the synchronization signal detection circuit 8, the transistor 6 is turned OFF, the output of the interface circuit 12 is set to HIGH, and the video signal changeover switch 10 is set to the input terminal 1 side ( 14).

It should be noted that the present invention is not limited to the above embodiments, and various modifications can be made based on the spirit of the present invention, and these are not excluded from the scope of the present invention.

[0014]

As described above in detail, the present invention provides the following effects.

(1) Even if the power of the decoder connected to the re-input terminal of the video equipment is OFF, the presence or absence of a synchronizing signal on the video signal line input to the re-input terminal is detected and the changeover switch is activated. Since the switch is switched to the normal video signal side connected inside the video equipment, it is no longer possible to view unscrambled video signals.

(2) By providing an independent switching switch, it is possible to cope with the case where there is no video signal and only the audio signal is broadcast in a scrambled manner.

(3) By using the I/O port of the microcomputer as an independent switching switch, when independent switching is not being performed, the microcomputer can recognize the output state of the synchronization signal detection circuit, As a result, it is possible to display an appropriate operating method in the event of an erroneous operation.

[Brief explanation of the drawing]

FIG. 1 A schematic configuration diagram of an automatic video signal switching circuit showing one embodiment of the present invention.

[Figure 2] Schematic configuration diagram of a conventional switching circuit example

[Explanation of symbols]

1 to 5 Resistor 6 Transistor 7 Microcomputer 8 Synchronous signal detection circuit 9 Scramble decoder 10 Video signal switching circuit 11 BS tuner 12 Interface circuit 13 I/O port 14 Input terminal 1 15 Input terminal 2 16 Video re-input terminal 17 Audio re-input Input terminal 18 Decoder output (bit stream, AFC detection output) 19 BS video output 20 BS audio output 21 Audio signal changeover switch 22 linked to 10
mechanical interlock switch

Claims (3)

[Claims] Claim 1: Two systems of video signal input terminals (input terminal 1,
an input terminal 2), a video signal switching circuit that switches the video signal, an audio signal switching circuit that operates in conjunction with the video signal switching circuit, and a circuit that detects a synchronization signal of the video signal input to the input terminal 1. In the video equipment equipped with this, when a synchronizing signal is detected in the previous synchronizing signal detection circuit, the video signal switching circuit is switched to the input terminal 1 side, and when a synchronizing signal is not detected, the video signal switching circuit is switched to the input terminal 1 side. A video signal automatic switching circuit characterized by switching to the terminal 2 side. 2. The video signal switching circuit according to claim 1, further comprising a forced changeover switch capable of independently switching the video signal switching circuit to the input terminal 1 side even if a synchronization signal is not detected in the previous synchronization signal detection circuit. Video signal automatic switching circuit. 3. In a video device incorporating a microcomputer having an I/O port that can switch between an input mode and an output mode, the I/O port can be connected to the I/O port even when a synchronization signal is not detected in a previous synchronization signal detection circuit.
By using the video signal switching circuit as an output mode for independently switching to the input terminal 1 side,
When the I/O port is to function as the forced changeover switch, and when switching is not performed independently, the I/O port is
The configuration is such that the input mode is switched to high impedance, the output of the synchronization signal detection circuit is detected, and the microcomputer is made to recognize the presence or absence of the synchronization signal on the input terminal 1 side, and the output of forced switching and the state during automatic switching are configured. 2. The automatic video signal switching circuit according to claim 1, wherein one I/O port is used for detection.