A character broadcast which can insert a signal for character broadcast for a V blanking period of time of a video signal and can reproduce character data on the reception side has been put into practical use. A character multiplex broadcast will now be described hereinbelow.
At present, a character broadcast signal is, as shown in FIG. 1, multiplexed into total eight lines of 14, 15, 16, 21 H (odd number fields) and 277, 278, 279, 284 H (even number fields) in the vertical blanking period (VBL) of a TV signal and is transmitted.
One line comprises a data line (296 bits), in which data of a clock run-in CR (16 bits) for obtaining bit synchronization and a framing code FC (8 bits) for obtaining byte synchronization and a check code (82 bits) for error correction are included. When eliminating them, a data amount per one H is equal to 190 bits.
In the character multiplex broadcast, tens of different programs are transmitted with respect to one TV broadcasting channel. Generally, one character broadcasting program comprises a plurality of pages. Those programs are sent as by a batch type in which whole data (all pages) of one program is transmitted in a lump or a non-batch type in which the data is sent on a page unit basis.
One character broadcasting program needs data of the unit of kilobyte (1 kilobyte=8192 bits). However, since only 190 bits can be stored per one line as mentioned above, the data is sent by using a number of lines.
In the character multiplex broadcast, data of one character broadcast program is sent by using same H (horizontal period) line.
In case of the batch type, data can be transmitted for, for example, one second or shorter even by using the same line. In case of the non-batch type, however, since the data of the other character broadcasting program is transmitted between pages, the data of each page is sent once in a while.
In this case, when the user designates a program number which doesn't exist by using a remote controller or the like, there is no response for a long time, so that there is a remarkable inconvenience. Therefore, even in the non-batch type, data of one page is certainly transmitted at an interval of 20 or 30 seconds, thereby preventing such an inconvenience. On the other hand, it is recommended that program index data of the line is also transmitted at the same interval.
FIGS. 2A and 2B shows a hierarchy structure of the data until a character broadcast is presented on the screen. At a head position of a data packet of each data line, PFX (prefix) of 14 bits certainly exists and functions as an ID of the packet. In detail, the PFX includes:
______________________________________ SI (service ID information) 8 bits CI (packet control code) 4 bits TF (transmission control flag) 1 bit IF (error detection coding interval ID flag) 1 bit ______________________________________
176 bits subsequent to the PFX are provided as a data block.
A plurality of data blocks are collected, thereby constructing a data group. A plurality of data groups are collected and construct a program. Each program starts by program management data and comprises several page data.
FIG. 3 shows a data block of one arbitrary program. At first, there is a program management data block. The block is EQU CI=0,TF=1,IF=1
In this block, there is a program data header called a PRCI (refer to FIG. 4). A magazine number is used for expansion in the future and is set to only 0 at present. When receiving the character multiplex broadcast, it is unnecessary to especially designate the magazine number. As program numbers, decimal numbers of three digits are prepared. The total page number shows the number of all pages of the program. A function level is set to 0 when it is used as a level specified as a fundamental function and is set to 1 when it is used as a level including an additional function.
As for program forms,
0: independent type program PA1 1: complementary program PA1 2: subtitle program PA1 DGI=0 indicates program management data, page data PA1 DCI=F indicates program index data
are shown. A program contents updating flag changes from 1 to 0 or 0 to 1 when the contents are changed.
Subsequently, there is a page data header block. The block is, EQU CI=1,TF=0,IF=1
in the non-batch type; EQU CI=n,TF=0,IF=1(n=0 to F)
in the batch type.
In the block, there is a page data header called a PACI (refer to FIG. 5). The belonging program No. of the page and the page No. (decimal notation and two digits) are recorded in the PACI.
Actual character data comprises a header sentence shown in the upper portion of the screen and a text. Both of the header sentence and the text are constructed by character codes determined by JIS. Since a data packet of one H line is set as a reference, NUL data is recorded in the remaining areas and a CRC code (error detection code) is recorded so as to certainly exist at the end of the data block. In FIG. 3, "ETX" means "end of text" and "ETB" means "end of transmission block". ETB is recorded at the end of the header sentence data because the block is finished there. ETX is recorded at the end of the text. The appearance of ETX means that there are further other pages and the text still continues. An end of transmission code EOT is recorded at the end position of the actual text of the final page.
Program index data is distinguished by DGI (data group ID code) in the data group header in FIG. 3.
Since the program index data is not a program, it is handled as a mere page. At that time, a format as shown in FIG. 6 is prepared as PACI. The program Nos. of the H line are arranged as text data after PACI. It is not obviously intended to display.
Subsequently, an European character multiplex broadcasting signal (alias, TELETEXT) will now be described. It is also called as UK system or WST (World System TELETEXT). As shown in FIG. 7, the WST is a system in which the signal is multiplexed to total 25 lines of 6 H to 22 H (odd number fields) and 318 H to 335 H (even number fields) in the vertical blanking period (VBL) of a TV signal and is transmitted. In the present situation, the broadcast is performed by using at least four lines or at most 15 lines among them. However, the number of H lines which are used are also different depending on a country or a broadcasting station. One line comprises a data line (360 bits), in which data of the clock run-in CR (16 bits) for obtaining a bit synchronization and the framing code FC (8 bits) for obtaining a byte synchronization is included. A data amount per one H is equal to 336 bits. The check code for error correction for every H line existing in the Japanese character multiplex broadcast doesn't exist.
In the WST, in a manner similar to the character multiplex broadcast, tens of different programs are transmitted with respect to one TV broadcasting channel. However, there is no concept of the program number. Although one program is constructed by almost one page, there is a case where one program is constructed by a plurality of pages. On the other hand, there is also a case where one page has a plurality of subpages.
In case of the WST, a program is also sent by using a number of lines. However, it is not always limited that one page data is sent by using only the same H (horizontal period) lines as in the Japanese character multiplex broadcast but all of H lines to be used are used. This is because data is transmitted by using at most 7-bit ASCII code (1-byte code) by only the alphabets without needing Chinese characters as in Japan (a Chinese character needs a two-byte code). As mentioned above, it is based on that the total amount of data is small. That is, this is because even if the number of apparent transmitting channels is not increased by fixing the H lines, other pages can be soon successively transmitted.
FIG. 8 shows data blocks of one arbitrary page. PFX (prefix) of 16 bits exists at the head of a data packet of each data line. In FIG. 8, two bytes in which a magazine and a packet address are written correspond to the PFX. The magazine, packet address, and page will now be explained. In the diagram, "P" means a parity and "D" means data.
For instance, a 150 page in the WST means the magazine No. 1 and the page No. 50. By combining both of them, they are handled as a page. One magazine comprises packets of 0 to 29. Exceptionally, only magazine No. 8 has a packet 30. Such a state is expressed as a packet 8/30. The packet 8/30 is used as a service data packet of the broadcasting station, for example, it is used for a PCD control of timer reservation or the like. Due to this, the packet 8/30 is transmitted at an interval of about one second.
A packet X/0 is a page header packet. As contents, as shown in FIG. 8, the page number, page subcodes, control bits, and 32 characters as a header sentence are inserted. Each character is set to an ASCII code of seven bits in which an odd number parity is added to the MSB.
Packets of X/1 to X/25 are text data packets. Data itself of forty characters per one line is stored to the packets. That is, in the WST, a picture plane itself of one page is transmitted. As for a protection of each character, only the parity of at most one bit is protected, so that a change in character often occurs due to a bad state of a TV signal. Even in such a case, however, since the characters are constructed by only the alphabets, such a character change can be judged from the relation between the front and back characters. B y waiting for a little while, the same page will be transmitted, so that the character change can be corrected there.
Packets X/26 to X/29 are text auxiliary data packets. Control information indicating whether the character code sent once by the text packet is displayed by, for example, flashing or inverting black and white is stored into those packets. In the Japanese character multiplex broadcast, those control information is included in the text and is expressed by a form such that the character as a control target is sandwiched.
In the WST, as mentioned above, alphabets are fundamentally used as data and a repeating period of each page is fast, so that a waiting time for the user is not so longer than that in the Japanese character multiplex broadcast. At the lowest stage shown in FIG. 8, a case where the page subcode is equal to 3F7Eh and the page No. is equal to FEh is set to page index data. Data such as the number of subpages of each page or the like is transmitted as such page index data. On the other hand, in order to improve the use efficiency for the user, a man-machine interface called an FASTEXT (or FLOF) in England and called a TOP in Germany has already been executed, so that there is hardly a possibility such that the user erroneously operates.
In case of receiving the foregoing character broadcast program, a time which is necessary to receive the whole data of one program is at most tens of minutes, although it is different in dependence on individual program contents. Such a time also includes a transmitting time of program data except the programs which the user wants to watch. So long as such a time can be eliminated by some device, a time that is required to watch the actual character broadcasting program can be reduced.
When considering that such an improvement is performed on only the reception side, for example, a viewer previously designates a desired character broadcasting program and after all of the program data was received, the viewer watches the program, so that the waiting time for the data reception can be eliminated. Among the character broadcasting tuners which are commercially available at present, there is a tuner using a semiconductor memory which can correspond to such a problem. However, an amount of program data that can be stored is limited according to such a tuner.
On the other hand, a construction such that a conventional VCR and a character broadcasting tuner are combined and the character broadcasting picture plane itself decoded by the character broadcasting tuner recorded and reproduced is also considered. In this case, however, a consumption amount of tape is remarkably larger than the information to be recorded. This is because substantially the same picture plane is continuously recorded for about twenty to thirty seconds from a time point after one page data was transmitted until a time point when the next page data is transmitted. According to such a method, not only the consumption amount of the tape increases but also it takes a time to retrieve the page upon reproduction.
When the recording is performed by the timer reservation, there is a fear such that the whole target program cannot be recorded by only the designation of the recording start and end times of one character broadcasting program.
Further, information regarding the actual TV broadcast, for example, a subtitle broadcast or a complementary program which transmits an outline or the like cannot be simultaneously recorded.
Therefore, an object of the invention is to provide a magnetic recording and reproducing apparatus made in consideration of the above mentioned problems.