GB2225519A - Teletext data encoding/decoding method - Google Patents

Teletext data encoding/decoding method Download PDF

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Publication number
GB2225519A
GB2225519A GB8925340A GB8925340A GB2225519A GB 2225519 A GB2225519 A GB 2225519A GB 8925340 A GB8925340 A GB 8925340A GB 8925340 A GB8925340 A GB 8925340A GB 2225519 A GB2225519 A GB 2225519A
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United Kingdom
Prior art keywords
signal
clock
teletext
bits
bit
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Granted
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GB8925340A
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GB8925340D0 (en
GB2225519B (en
Inventor
Osamu Yamada
Toru Kuroda
Akio Yanagimachi
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Japan Broadcasting Corp
Original Assignee
Nippon Hoso Kyokai NHK
Japan Broadcasting Corp
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Priority claimed from JP28586788A external-priority patent/JPH02132985A/en
Priority claimed from JP4328389A external-priority patent/JPH02224493A/en
Application filed by Nippon Hoso Kyokai NHK, Japan Broadcasting Corp filed Critical Nippon Hoso Kyokai NHK
Publication of GB8925340D0 publication Critical patent/GB8925340D0/en
Publication of GB2225519A publication Critical patent/GB2225519A/en
Application granted granted Critical
Publication of GB2225519B publication Critical patent/GB2225519B/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00Television systems
    • H04N7/08Systems for the simultaneous or sequential transmission of more than one television signal, e.g. additional information signals, the signals occupying wholly or partially the same frequency band, e.g. by time division
    • H04N7/087Systems for the simultaneous or sequential transmission of more than one television signal, e.g. additional information signals, the signals occupying wholly or partially the same frequency band, e.g. by time division with signal insertion during the vertical blanking interval only
    • H04N7/088Systems for the simultaneous or sequential transmission of more than one television signal, e.g. additional information signals, the signals occupying wholly or partially the same frequency band, e.g. by time division with signal insertion during the vertical blanking interval only the inserted signal being digital
    • H04N7/0882Systems for the simultaneous or sequential transmission of more than one television signal, e.g. additional information signals, the signals occupying wholly or partially the same frequency band, e.g. by time division with signal insertion during the vertical blanking interval only the inserted signal being digital for the transmission of character code signals, e.g. for teletext
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04NPICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N7/00Television systems
    • H04N7/025Systems for the transmission of digital non-picture data, e.g. of text during the active part of a television frame
    • H04N7/035Circuits for the digital non-picture data signal, e.g. for slicing of the data signal, for regeneration of the data-clock signal, for error detection or correction of the data signal

Abstract

A TELETEXT clock signal in simple frequency relation with the color subcarrier fsc of the PAL color television system is generated from the subcarrier, and the block length of a signal section of each packet is set to 272 bits, thereby making applicable the (272, 190) code which is the same error-correcting code as in the Japanese system (Fig 1). At receiving apparatus (Fig 7), a color subcarrier signal is extracted from the PAL color television signal, and is used to generate a signal of the same frequency and the same phase as the clock run-in signal such as for TELETEXT broadcasting by an APC circuit or the like. With this signal as a clock signal, the scanning line number is counted from the first field of the television signal and at the same time, if TELETEXT signals or the like are multiplexed, the framing code is detected thereby to reproduce the framing code timing by front and back protection.

Description

METHOD OF TRANSMITTING TELETEXT SIGNALS AND APPARATUS FOR RECEIVING THE SAME The present invention relates to a method of transmitting TELETEXT signals and an apparatus for receiving such signals, or more in particular to a method of transmission and an apparatus for reception in which the ability of correcting an error in a TELETEXT boradcasting of the PAL color television system is strengthened.
The TELETEXT broadcasting means a broadcasting in which signals are sent superimposed or multiplexed on the television wave and information including characters, simple patterns, etc. are displayed on the cathode ray tube separately from a television program.
The conventional TELETEXT broadcasting of the PAL color television system employs a British method called System B as determined by CCIR (comity Consultatif International des Radiocommunication). This method placing no great emphasis on the error correstion is not suitable for a receiving apparatus in an area severe in receiving conditions or for a system using the ideogram like the one in China.
The Japanese system, on the other hand, which has been under development with primary emphasis placed on the error correction from the very beginning, has been completed as a very strong system against an error by employing a (272, 190) code.
In the Japanese system, the continuity of clock signal and the phase of a framing code are held between packets, and therefore the framing code is received so weakly under normal receiving conditions that full ability of correction of subsequent (272, 190) code could not be achieved. The ability to correct the (272, 190) code, however, has since been improved by means of detecting a framing code timing through front and back protection.
It is therefore possible to secure a framing code timing as long as there occurs no continuous detection errors even if a detection error is caused in the framing code by an impulse or random noise.
In contrast, British or other foreign systems process signals only within a single packet, and therefore the clock frequency has not even a simple relationship with the color subcarrier frequency. In the event that a framing timing cannot be taken by an error caused in the framing code, therefore, all the signal in the particular packet would be lost. As to the error correction code, on the other hand, only the (8, 4) enlarged code is employed with the ability to correct an error of one out of eight bits, while only an error detection code for detecting an error of one out of eight bits is used for other code portions.
As a result, the problem has been posed that an erroneous character is reproduced or important information cannot be transmitted in an area severe in receiving conditions.
The disadvantages of the above-mentioned method of TELETEXT broadcasting of the PAL color television system will be described in detail below.
The characters broadcasting multiplexed on the television signal of the PAL color television system conventionally known includes a character braodcasting developed in England and called "Ceefax". In this system as shown in Fig. 6, TELETEXT signals are multiplexed as 360 bits for each packet with the bit rate of 6.9375 Mbps, including the leading 16 bits as a clock run-in signal for securing bit synchronism, followed by eight bits of a framing code signal made up of a predetermined pattern for discriminating a signal boundary, further followed by information section of 336 bits providing the substance of the signal.
Exactly 444 bits are represented by a 1H period.
As a result, according to the Brithish system, there is no direct frequency relationship designated between the clock rate and the color subcarrier.
Also, in spite of a predetermined frequency relationship held between the clock rate and the horizontal sync signal frequency, it is difficult to reproduce the clock signal from the horizontal sync signal due to the facts (1) that the gain cannot be secured from an APC circuit and (2) that a phase jitter is liable to be caused by the horizontal sync timing imemdiately after vertical synchronization.
For these reasons, the Ceefax does not take the frequency relations with the television signal into consideration, but employs a receiving apparatus for processing signals for each packet. This eliminates the need of phase coincidence of the leading bit of the packet signal for each scanning line (H) as a transmission signal, and there is posed no problem at all by multiplexing in different phases.
Specifically, at the receiving end, clock synchronization is assured by the leading 16 bits of a packet singla to extract a framing pattern. If the framing pattern has an error of a bit, it is possible to extract the timing thereof. If there is an error of two or more bits, however, the extraction of timing is impossible, and the particular packet signal becomes unusable.
The Ceefax system thus has a serious disadvantage in that the framing code is received only weakly as compared with the Japanese system in which the framing code is received with front and back protection. In the case where the ability of receiving the framing code is low, the system is useless no matter how strong is the subsequent ability of correcting signal errors.
As mentioned above, the Ceefax system fails to take the error correction into full consideration, and the character code subsequent to the framing code has only a 7-bit code with a 1-bit parity added thereto.
The function is thus limited to the error detection.
As will be seen from the foregoing description, the method of the television multiplex TELETEXT braodcasting (Ceefax) of the PAL color television system easily succumbs to a bit error, and is not suited to a system for sending an ideogram such as Japanese or Chinese having a great amount of information for each character or a system for transmitting a great amount of information (such as a tele-software for sending a computer program).
The object of the present invention is to provide a method of transmitting TELETEXT signals of the PAL color television system and an apparatus for receiving the same with an improved error correction ability.
In order to achieve this object, there is provided a transmission system according to the present invention, comprising means for extracting a color subcarrier signal from a television signal of the PAL color television system, means for generating a clock signal for TELETEXT signals in a simple integral ratio with the color subcarrier signal, and means for sequentially transmitting signals of a total of 296 bits including a 16-bit clock run-in for clock synchronization, an 8-bit framing code for framing timing, a 190-bit information and an 82-bit parity signal computed from the 190-bit information, from a specific vertical blanking period.
According to another aspect of the present invention, there is provided a receiving apparatus comprising reproduction means for reproducing a signal of the same frequency as TELETEXT signals from a color burst signal thereby to reproduce a signal of the same phase as the multiplexed clock run-in and protective means for detecting a framing code and providing front and back protection utilizing the fact that the framing code is multiplexed at each predetermined timing, thereby receiving a framing code securely against a receiving error.
As seen from above, according to the present invention, a clock signal having a predetermined frequency relationship with the color subcarrier of the television signal of the PAL color television system is used, and while maintaining the continuity of the clock signal, the clock frequency is determined in such a manner that the same (272, 190) code as employed in the Japanese TELETEXT broadcasting is superposed on line 1H of the PAL signal, thereby providing the same powerful error-correcting ability as in the Japanese TELETEXT broadcasting.
The above and other objects, features and advantages will be made apparent by the detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a block diagram showing an example of a circuit for generating a television signal according to the present invention; Fig. 2 is a diagram showing an example of packets multiplexed at intervals of 362 bits; Fig. 3 is a diagram showing an example of packets multiplexed at intervals of 361 bits; Fig. 4 is a diagram showing a vertical blanking period of a PAL color television signal; Fig. 5 shows relative positions of packet signals; Fig. 6 is a diagram showing TELETEXT signals called "Ceefax"; Fig. 7 is a block diagram showing an embodiment of a TELETEXT signal-receiving apparatus according to the present invention; and Fig. 8 is a block diagram showing a framing code generation circuit.
Now, the present invention will be described in detail with reference to an embodiment.
First, reference is had to the basic principle of a tranmission system.
The frequency fSC of the color subcarrier of the PAL color television system is defined as fSC = 4433618.75 Hz On the other hand, the clock frequency fCL of the TELETEXT signals is given preferably in the form of CL in fSC where m and n are simple integral numbers. In the PAL color television system, the period T of a frame is expressed as T = 1 = 40 x 10-3 (secs) 25 The condition required for maintaining the continuity of the clock signal is TCL x N = M x 40 x 10 where N is the number of clock pulses in the period involved and M the number of frames considered in terms of full frames.Thus N = M x 40 x 10 TCL x fsc x M x 40 x 10-3 = m = n x M x 177344.75 m The number N is required to be an integral number satisfying this equation.
If the clock signal is to maintain continuity when M is unity, that is, when the number of frame is one, m/n takes the value of 12/11, 16/11, 20/11 or the like. Under this condition, the bit rate is 4.836675 MHz, 6.44890 MHz, 8.061125 MHz or the like respectively. It is thus impossible to multiplex 296 (= 272 + 8 + 16) bits in a period of about 54 microseconds where the PAL color television signal may be multiplexed.
In the case where M is two, on the other hand, the number of rames is two, and the relationship m/n = 12/11, 14/11, 16/11 or the like must be held for securing the continuity of the clock signal. Except for m/n = 14/11, the condition is the same as when continuity is maintained for a single frame mentioned above. The bit rate for m/n = 14/11 is 5.6427875 MHz, which is substantially equal to the bit rate of 5.727 MHz for the Japanese TELETEXT braodcasting system.
Also, the number of bits that may be multiplexed during the period of about 54 microseconds is 304.7 bits, which is sufficient for multiplexing 296 bits as required.
The length 1H of the PAL color television signal represents exactly 64 microseconds. Therefore, the number of bits that can be multiplexed in 1H is 361.1384 (= 64 x 5.6427875), which is substantially equal to the number 364 for the Japanese version. If the clock of continuous phases is multiplexed by 296 bits for each 1H at this bit rate, the phase of the leading bit is displaced by about a bit slightly after 8H. The number of bits one frame later is 225711.5, so that the phase in the second and subsequent frames is displaced by 0.5 bits as compared with the first frame, while phase is matched in the third and subsequent frames.
As mentioned above, if an error-correcting ability as strong as that of Japan is to be secured in a system for multiplexing TELETEXT signals on the PAL color television signal, a method is recommended in which the frequency 14/11 of the color subcarrier is used as a bit rate.
In the PAL color television system, TELETEXT signals may be multiplexed during the vertical blanking period of 8H to 25H and mating fields thereof. Therefore, if packet signals of 272 bits are multiplexed sequentially from 8H, the multiplexing position is displaced for each H by setting the packet period to 362 bits (See Fig. 2). The amount of this displacement is equivalent to 0.8616 bits. The amount of displacement up to 25H, therefore, is given as 14.6472 (= 0.8616 x 17) bits. The length of time corresponding to this amount is 2.595738365 (used) (= 14.6472 x 1/5.6427875).
Handling at the receiving end will be facilitated, therefore, if a time margin as much as this is given at the last portion of the packet signal multiplexed in the first line 8H and a packet signal associated with each H is multiplexed every 362 bits.
In this case, however, as viewed on the same H from the leading bit multiplexed in line 8H to the last bit multiplexed in line 25H, the total length is given as (296 + 14.6472)/5.6427875 = 55.05208197 (psec) since each packet signal multiplexed in each line H has a multiplexed position displaced each other little by little.
On the other hand, there is ten microseconds available till the end of the color burst of the PAL color television signal, and 64 microseconds is represented by 1H. Therefore, a multiplexable period available is at most 54 microseconds. Since the amount of displacement is more than 54 microseconds, multiplexing is impossible under this condition.
Now, if a packet signal is multiplexed in cycles of 361 bits (Fig. 3), the phase is advanced by 0.1384 bits for each H. In this case, the length of 18H from lines 8H to 25H is given as (296 + 17 x 0.1384)/5.6427875 = 52.87330065 (used) which is covered by the time length 54 ps. Since there is available 10 microseconds till the last portion of the color burst, however, the time margin available for multiplexing is 54 - 52.8978275 = 1.1021725 (used) This time margin is very limited although multiplexing is not impossible.
The original length 296 bits of one packet covers 296 x 1/5.6427875 = 52.45634361 (used) In the case shown in Fig. 3, on the other hand, difference is 52.87330065 - 52.45634361 = 0.41695704 (psec) As seen from this, the time becomes only slightly longer in this case.
As compared with "Ceefax" shown in Fig. 6.
52.87330065 - 51.89189189 = 0.98140876 (used) The extension of data length is less than one microsecond, thereby leading to substantially the same packet length as Ceefax.
Further, the packet head may be changed from one packet to another. Assuming that the clock run-in begins from the 361st bit in line 9H following 8H, for example, 10H may start with the 362nd bit.
As compared with when the clock run-in is assumed to start every 361 bits, the phase displacement from the clock run-in first multiplexed is six or seven times large when the clock run-in is assumed to begin every 362 bits. Therefore, a packet with the clock run-in having 362-bit cycles may be inserted 362 bits after every 6 or 7H where the clock run-in starts every 361 bits.
The foregoing explanation involves all multiplexable lines during the vertical blanking period, and therefore the multiplexing for every 361 or 362 bits may of course be effected if multiplexable lines H are limited.
Even in the method mentioned above, the information block of 272 bits may be shortened in the absence of a margin with the color subcarrier. For example, the block length of 264 (= 272 - 8) or 256 (= 272 - 16) bits may be considered. Also, the information bits of the (272, 190) code is 190, which is not given in bytes, and therefore, if the number 266 (= 272 - 6) or 258 (= 272 14) is used as bits, the information bits involved may be expressed as 184 bits = 23 bytes and 176 bits = 22 bytes respectively, thus facilitating the handling of data. Even in this case, the signal starting from the clock run-in may be arranged for each H at the intervals of 361 or 362 bits.
A method of multiplexing in the vertical blanking period at the starting point of a frame is mentioned above. Apart from this, consideration must also be given to the vertical blanking period of the next field. Assuming that the first line number of the next field is 313H, the multiplexable lines are 17H from the 321st line. This relationship is shown in Fig. 4.
If a packet arrives for each 361 or 362 bits, however, a considerable displacement would occur inconveniently at the line 321H. Arrangement is made, therefore, to multiplex after every predetermined clock length from line 8H. Further, in the next field, multiplexing is made from line 633H, after another predetermined clock length. In this case, however, the phase of the clock signal is displaced from the first field by 0.5 bits. This is because two frames of 14/11 x fSC defined herein provides one period.
In Fig. 4, consider on the basis of 8H. The displacement in bit clock at line 321H of the next field is given as 313 x 64 x 5.6427875 = 113036.3192 bits Further, after 312H in the next field, the figure is 312 x 64/5.6427875 = 112675.1808 bits At the point of the same timing after one frame, the displacement is 113036.3192 + 112675.1808 = 225711.5 bits The displacements in a fraction of a bit at these timings are 0.05656778675 microseconds, 0.03204090177 microseconds and 0.08860868852 microseconds respectively.
As a result, if the phase of clock run-in of the packet signal multiplexed on line 313H is the 113036th clock, and the corresponding phase on the line which is 312 after (which is equivalent to one frame after) is the 112674.5 bit, (which means that the phase is displaced by half of a bit after one frame), then the phase becomes continuous in cycles of one frame.
Fig. 5 is a diagram showing relative positions of packet signals.
A circuit for generating a television signal according to the present invention is shown in Fig. 1.
In Fig. 1, reference numeral 101 designates a color subscarrier signal (4.43361875 MHz), numeral 102 a frame pulse for shifting the clock phase by half bit for each frame, numeral 103 a horizontal sync signal for counting the number of lines H, numeral 104 a character data sent from the computer, numeral 105 a normal PAL color television signal, numeral 106 a line number designation signal for designating the multiplexing lines H, numeral 107 a frequency divider circuit, numeral 110 a voltage controlled oscillator (VCO), numeral 111 a phase control circuit for controlling the clock phase, numeral 112 a phase shifting circuit for shifting the clock phase by half bit for each frame, numeral 113 a DMA controller for reading data out of a memory 114 at a timing explained above, numeral 114 a memory for storing the sent data temporarily, numeral 115 and address and a control signal for controlling the memory 114, numeral 116 a multiplexing packet data, and numeral 117 a multiplexer for multiplexing the television signal on a designated line.
Now, the operation of this signal generator will be explained.
A PAL circuit made up of a color subcarrier frequency divider 107 and the VCO 110 for the PAL color television signal provides a signal of 5.6427875 MHz as intended. This signal is regulated by the phase controller 111 to produce a data output signal in right phase. This signal is also displaced by half bit for each frame by a frame pulse, so that a packet signal for each frame is produced at the same timing as the horizontal sync signal.
With this output as a clock signal, the DMA controller 113 is controlled by frame timing and H sync signal, and an address signal and a control signal are produced from the DMA controller 113 in such a manner as to produce the data at the timing described above.
The signal from the DMA controller 113 causes the data already stored in the memory 114 to be produced and multiplexed on a designated line of the television signal by the multiplexer 117. The clock run-in and the framing code are of course predetermined signals, and therefore they may be produced from a fixed memory region such as ROM instead of from the memory 114.
A basic configuration is shown in Fig. 1, and the memory output data 116 is naturally subjected to band limitation due to a cosign roll-off filter or the like (not shown) at the input of the multiplexer 117.
Now, a receiving apparatus will be explained.
An embodiment of the TELETEXT signal-receiving apparatus according to the present invention is shown in Fig. 7. In Fig. 7, numeral 201 designates a PAL color television signal on which TELETEXT signals are multiplexed by the aforementioned method according to the present invention. Specifically, the bit rate is (14/11) x fSC, where fSC is the color subcarrier frequency of the PAL color television signal and is given as fSC = 4.43361875 MHz The bit rate of the TELETEXT signals is 5.6427875 Mbps.
Numeral 202 designates a color subcarrier reproduction circuit for producing a color subcarrier signal of 4.43361875 MHz reproduced as a continuous signal by an APC circuit from the color burst signal multiplexed on each line H.
Numeral 203 designates a frequency divider circuit for dividing the color subcarrier frequency into components of one eleventh. The output signal of the frequency divider circuit 203 thus has a frequency of 0.40305625 MHz.
Numeral 204 designates a phase comparator circuit for generating an input signal to the VCO 205.
The output frequency of the VCO 205 is 5.6427875 MHz, which is divided into components of one fourteenth (1/14) by the frequency divider circuit 206. The frequency of the output signal of the frequency divider circuit 206 is the same 0.40305625 MHz as the output signal frequency of the frequency divider circuit 203.
The output signal of the VCO 205 is applied to a phase selection circuit 207 to prepare signals of various phases. The phase may be displaced, for example, by 10 ns for each signal.
Numeral 208 designates a clock run-in extraction circuit. The frequency of the clock run-in signal 209 is the same as the output signal frequency of the VCO 205, and a signal nearest to the phase of the clock run-in signal 209 is selected out of the signals of various phases prepared at the phase selection circuit 207 and is produced as a signal 210. More specifically, the signal 210 and the clock run-in signal 209 are substantially phase-locked with each other.
Numeral 211 designates a vertical sync signal detection circuit, which detects only the first field in particular. A multiplexing timing signal for the second field is produced from the framing code generation circuit 214 through an H counter 213.
Numeral 212 designates a horizontal sync timing signal generation circuit for generating a signal for counting H pulses.
Numeral 215 designates a circuit for detecting the framing code of an input signal as an input signal to the framing code generation circuit 214. This framing code generation circuit 214 is for providing front and back protection of the framing code by a signal for designating the line H of the output signal 217 of the H counter 213, a clock signal 210, an identification signal 209 for deciding whether a multiplexing H exists or not, a framing code detection signal 215 and the like.
On the basis of the timing of the output 216 of the framing code generation circuit 216, only the data section (data train subsequent to the framing code) of the packet signal (output of the packet signal detection circuit 217) is extracted accurately through a data extraction circuit 218.
The phase selection circuit 207 should be reversed in phase by 1800 automatically in the first field by the configuration shown in Fig. 7. The output of the vertical sync signal detection circuit 211 may be used, however, to shift forcibly to a signal 1800 different in phase.
A detailed circuit configuration of the framing code generation circuit 214 in Fig. 7 is illustrated in Fig. 8. Numeral 301 designates a PAL color television signal, numeral 302 a signal 210 generated in Fig. 1 (clock signal reversed in phase by 1800 for each first field), numeral 303 a gate signal indicating the periods of 8 to 25H and 312 to 329H where TELETEXT signals may be multiplexed, numeral 304 a gate signal for only 8H, numeral 305 a framing code detection signal, numeral 306 a 361-bit counter, numeral 307 an AND circuit, numeral 308 a 113036-bit counter, numeral 309 an AND circuit, numeral 310 a coincidence detection circuit, numeral 311 a non-coincidence detection circuit, numeral 312 a coincidence pulse, numeral 313 a noncoincidence counter, numeral 314 a coincidence counter, numeral 315 a non-coincidence counter output signal, numeral 316 a coincidence counter output signal, numeral 317 an AND circuit, numeral 318 an AND circuit, numeral 319 a framing timing signal from the internal counter, numeral 320 a 113036-bit counter output signal, and numeral 321 a framing timing output signal.
The operation of the circuit shown in Fig. 8 will be described below from one part to another.
In initial stages, the timing signal detected by the framing code detection circuit 305 is passed through the gate 309 to reset the 361-bit counter 306. After that, the clock signal 302 is counted by the 361-bit counter 306 thereby to generate an internal framing code signal 319. This counter 306 is adapted to be operated only during the period from 8 to 25H or from 312 to 329H where signals are multiplexed.
The output signal 319 of the internal counter is always compared with the output of the framing code detection circuit 305. A signal indicating whether the TELETEXT signal 303 is multiplexed or not is produced by detecting a clock run-in or the like.
An output signal compared at the coincidence detection circuit 310 makes up a non-coincidence signal 311 and a coincidence signal 312. Until the coincidence counter 314 counts up, the coincidence counter 314 is reset by the signal 317 always with the arrival of the non-coincidence signal 311. Specifically, the coincidence counter 314 is for counting the number of continuous coincidences and normally produces a count-up signal 316 when three framing code signals 316 are received in a row in the same phase. The other noncoincidence counter 313 is for counting the number of continuous non-coincidences and clears the coincidence counter 314 when the signal 315 is produced.
The head of the second field is reset by the timing of the framing code of the leading multiplexing line H of the first field of the gate signal 304 to count 113036 bits, the output of which resets the 361bit counter 306 again, thus generating an internal framing code.
The line 8H or 312H of the gate signals 303, 304 shown in Fig. 8 may be interpreted as the leading H in a field having a multiplexed signal.
The configuration of Fig. 8 permits accurate reception of the framing code of 296-bit TELETEXT signals multiplexed on the PAL color television signal.
It is assumed, however, that the line number such as 8H in the foregoing description is counted by the method shown in Fig. 4.
The TELETEXT signal train shown in Fig. 7 is decoded by the (272, 190) code and retrieved as a 190-bit data free of error. The CPU displays characters and patterns on the CRT by interpreting the 190-bit data.
As will be understood from the foregoing description, according to the present invention, the clock frequency of the TELETEXT signals multiplexed on the PAL color television signal is related to the color subcarrier frequency, thereby assuring the reproduction of the clock signal and the framing timing signal in the receiving apparatus.
If the clock signal frequency is set to (14/ll)fsc and the clock phase is reversed for each framing timing (40 msec) of the television signal, for example, the timing of the head of the packet signal may be rendered coincident sequentially for each time length of 40 msec displaced by half bit, thus facilitating the signal handling at the receiver.
In this way, 296 bits can be multiplexed for each pakcet in the same manner as the Japanese TELETEXT signals, thereby making applicable the (272, 190) code in a strong error-correction system. Also, the receiver, the only difference of which lies in the method of signal retrieval, is usable with the IC developed for the Japanese TELETEXT signal broadcasting.
Further, the coding system may be used directly.

Claims (6)

CLAIMS:
1. A method of transmitting TELETEXT signals comprising the steps of extracting a color subcarrier signal from the PAL color television signal, generating a clock signal for the TELETEXT signals in a simple integral ratio with the color subcarrier signal, and sequentially transmitting a 16-bit clock run-in for assuring clock synchronization, an 8-bit framing code for taking framing timing, a 190-bit information and an 82-bit parity signal computed from the 190-bit information for a total of 296 bits.
2. A method according to Claim 1, wherein the integral ratio is 14/11.
3. An apparatus for receiving the TELETEXT signals transmitted according to Claim 1, comprising means for reproducing a signal of the same frequency and the same phase with the clock run-in for TELETEXT braodcasting from a color subcarrier signal.
4. An apparatus for receiving the TELETEXT signals according to Claim 3, further comprising means for detecting a framing code by using the fact that the framing code is multiplexed at each predetermined timing, providing thereby a reliable reception of the framing code.
5. A method of transmitting teletext signals substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
6. An apparatus for receiving teletext signals constructed and arranged to operate substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.
GB8925340A 1988-11-14 1989-11-09 Method of transmitting teletext signals and apparatus for receiving the same Expired - Fee Related GB2225519B (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
JP28586788A JPH02132985A (en) 1988-11-14 1988-11-14 Transmitting system for character broadcasting signal
JP4328389A JPH02224493A (en) 1989-02-27 1989-02-27 Data signal receiver

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GB8925340D0 GB8925340D0 (en) 1989-12-28
GB2225519A true GB2225519A (en) 1990-05-30
GB2225519B GB2225519B (en) 1993-03-31

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GB8925340A Expired - Fee Related GB2225519B (en) 1988-11-14 1989-11-09 Method of transmitting teletext signals and apparatus for receiving the same

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GB (1) GB2225519B (en)
HK (1) HK132193A (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2229890B (en) * 1989-03-03 1993-09-01 Sanyo Electric Co Text broadcasting signal generating apparatus and text broadcasting signal receiving apparatus
WO1994017633A1 (en) * 1993-01-21 1994-08-04 Scientific-Atlanta, Inc. Apparatus and methods for providing close captioning in a digital program services delivery system
EP0660607A1 (en) * 1993-12-22 1995-06-28 Deutsche Thomson-Brandt Gmbh Method of receiving teletext data, which are transmitted in a television signal
US5629738A (en) * 1994-06-10 1997-05-13 Samsung Electronics Co., Ltd. Apparatus for generating a detection clock for detecting digital data contained in a composite video signal and a data detector using detection clock

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2229890B (en) * 1989-03-03 1993-09-01 Sanyo Electric Co Text broadcasting signal generating apparatus and text broadcasting signal receiving apparatus
WO1994017633A1 (en) * 1993-01-21 1994-08-04 Scientific-Atlanta, Inc. Apparatus and methods for providing close captioning in a digital program services delivery system
US5438370A (en) * 1993-01-21 1995-08-01 Scientific Atlanta Apparatus and methods for providing close captioning in a digital program services delivery system
EP0660607A1 (en) * 1993-12-22 1995-06-28 Deutsche Thomson-Brandt Gmbh Method of receiving teletext data, which are transmitted in a television signal
US5629738A (en) * 1994-06-10 1997-05-13 Samsung Electronics Co., Ltd. Apparatus for generating a detection clock for detecting digital data contained in a composite video signal and a data detector using detection clock

Also Published As

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HK132193A (en) 1993-12-10
CN1016552B (en) 1992-05-06
CN1043053A (en) 1990-06-13
GB8925340D0 (en) 1989-12-28
GB2225519B (en) 1993-03-31

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