JPS63296586A - Scramble circuit - Google Patents

Abstract

PURPOSE:To apply different scramble to a teletext data by inverting a digital value of the teletext data multiplexed onto a television video signal by an optional setting value given at each horizontal scanning period of a television video signal. CONSTITUTION:A counter 5 counts a sampling clock outputted from a sampling clock recovery circuit 3 and the count is outputted to a switching signal generat ing circuit 7. Moreover, a synchronizing separator circuit 2 in the setting circuit 6 outputs a synchronizing signal, which outputs an optional setting value at each horizontal scanning period to the circuit 7. In the switching signal generat ing circuit 7, the switching signal is given to a switching circuit 9 depending on the count outputted from the counter 5 and the setting value outputted from the setting circuit 6. On the other hand, an inverting circuit 8 inverts the digital value of the teletext data multiplexed on the television video signal, outputs the inverted signal to the circuit 9 and outputted to the television video signal output terminal 10.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a circuit for scrambling and transmitting teletext data multiplexed on a television video signal.

Conventional technology Teletext broadcasting, which is an example of multiplexing data onto a television video signal, is a system that multiplexes digital data such as image information consisting of text and graphics such as weather forecasts, news, and stock information, and audio information. It is a broadcasting system that transmits In this teletext, teletext data is multiplexed during the horizontal scanning period of the vertical blanking period of the television video signal. There is also full-field teletext, in which teletext data is multiplexed and transmitted not only in the vertical blanking period of a television video signal, but also in all horizontal scanning periods, including the portion where the normal video signal is present.

Problems to be Solved by the Invention In teletext broadcasting and Frere Field teletext broadcasting, when it is desired to limit the teletext data that a receiver can receive and receive the service, it is necessary to limit the teletext data except for the teletext data that is multiplexed on the transmitting side. was.

Furthermore, if it is desired to restrict the teletext data to be transmitted to a plurality of recipients differently, a transmission path for each recipient is required, which is uneconomical.

Means for Solving the Problems The present invention inverts the digital value of the teletext data multiplexed on the television video signal using an arbitrary setting value given for each horizontal scanning period of the television video signal. The teletext data can be scrambled differently for each horizontal scanning period.

According to the above, the present invention provides teletext data that the receiver can receive and receive service by giving as many of the setting values as the receiver desires as the key to unscramble the teletext data. can be freely restricted, and furthermore, confidentiality can be maintained for recipients who do not want to receive the service.

Embodiment FIG. 1 is a block diagram of a scrambling circuit which is an embodiment of the present invention. In the figure, 1 is a television video signal input terminal, and the television video signal input from 1 is input to a synchronization separation circuit 2, an inverting circuit 8, and a switching circuit 9. The television video signal input to the synchronization separation circuit 2 is separated into a synchronization signal and a data signal. The sampling clock regeneration circuit 3 regenerates the sampling clock of the teletext data according to the synchronization signal output from 2,
It is output to the teletext data detection circuit 4, counter 6, and inversion circuit 8.

4, the data signal output from the synchronous separation circuit 2,
Based on the sampling clock outputted from the counter 3, teletext data is detected and a teletext data gate signal is output to the counter 6. The counter 6 counts the sampling clock output from the sampling clock regeneration circuit 3 during the valid period of the teletext data gate signal,
The count value is output to the switching signal generation circuit 7.

Further, the setting circuit 6 outputs an arbitrary set value to the circuit 7 for each horizontal scanning period according to the synchronization signal outputted from the synchronization separation circuit 2. The switching signal generating circuit 7 outputs a switching signal to the switching circuit 9 based on the count output from the counter 6 and the set value output from the counter 6. On the other hand, the inverting circuit 8 inverts the digital value of the teletext data multiplexed on the television video signal input from 1, and outputs the inverted signal to 9. In the switching circuit 9, the television video signal input from 1 and 8 and the inverted signal input from 8 are switched by the switching signal input from 7, and outputted to the television video signal output terminal 10.

FIG. 2 shows that when the television video signal input to terminal 1 in FIG. This figure shows an example of a timing chart with respect to a television video signal C. As shown in Figure 2, the teletext data multiplexed on the television video signal a is
Teletext data can be scrambled differently for each horizontal scanning period.

Effects of the Invention As described above, the present invention can easily obtain high confidentiality using a simple η circuit, and is extremely effective when transmitting teletext data to a CATV network with a large number of receivers. be.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a scrambling circuit according to an embodiment of the present invention, and FIG. 2 is a 311PA showing an example of a timing chart of the same circuit. 1...TV video signal input terminal, 2...
・Synchronization separation circuit, 8...Inversion circuit, 10...
...TV video signal output terminal.

Claims (1)

[Claims] a circuit for reproducing, from a television video signal, a sampling clock for teletext data multiplexed on the television video signal; a circuit for outputting a gate signal indicating a multiplexing position of the teletext data; a counter that counts the sampling clock; a generator circuit that outputs a switching signal that changes according to an arbitrarily set count value for each horizontal scanning period of the television video signal; A scrambling circuit comprising a switching circuit that switches between a signal whose value is inverted and the television video signal, and scrambling the teletext data output from the switching circuit.