1. Field of the Invention:
This invention relates to an optical card reproducing apparatus which generates a pseudo synchronizing pattern detecting signal ensuring against a failure of the detection of a synchronizing pattern of a top portion of a recording region divided into a plurality in a recording medium.
2. Description of Related Art;
It is well-known to use an optical data recording and reproducing apparatus which can record and reproduce data by the radiation of a light beam instead of a magnetic system type data recording and reproducing apparatus which can record information data in a recording medium by using a magnetic head and reproduce the recorded information data.
An optical disk or optical card is used for the recording medium of the above mentioned optical data recording and reproducing apparatus.
In such recording medium, many tracks are formed on the recording surface, information data are recorded along the respective tracks and the recorded information data are reproduced.
The respective tracks are divided into a plurality of recording regions generally called sectors.
FIG. 1 shows an example of a sector format in an optical card of a generally used prior art.
Bit synchronizing patterns 51 and 52 for synchronizing signal recording regions for generating self clocks are provided at both ends of each sector so that self clocks may be generated by using a PLL (Phase Looked Loop) circuit from bit patterns obtained by scanning the synchronizing patterns 51 and 52.
In the top portions of the first block 53, second block 54, . . . and nth block 55 in which data are actually recorded, there are provided byte synchronizing patterns 56, 57, 58, 59 and 60 as information recording regions representing the top portions of these first block 53, second block 54, . . . and nth block 55. Thus, each sector is divided into n blocks.
In FIG. 1, the synchronizing patterns 51 and 52 are provided on both sides so that the data may be read out of either of the right and left sides
FIG. 2A shows an arrangement of data as stored in a memory so that an error correction may be made for the data in case the data can be normally read out. The data of the first block 53 enter the first line, the data of the second block 54 enter the second line and the data of the nth block 55 enter the nth line.
FIG. 2B shows an arrangement of read-out data as stored in a memory in case the byte synchronizing pattern cannot be detected by the influence of a dust or flaw on the optical card in case the data are to be read out of the left side, for example, in FIG. 1.
In such case, the second block 54 will enter the first line which the first block 53 should inherently enter, the third block 54 will enter the second line which the second block should enter, the nth block 55 will enter the (n-1)th line which the (n-1)th block should enter and nothing will enter the nth line which the nth block 55 should enter.
In a data recording and reproducing apparatus using such recording medium as an optical card, a Lead Solomon product sign is often used as an error correcting sign. In such case, as shown in FIG. 2C, first of all, the first error correction (C1 correction) will be made in each line, then, as a result of the C1 correction, the second error correction (C2 correction) will be made in each line.
In the data obtained where the byte synchronizing pattern at the top of the first block cannot be detected as in FIG. 2B, if the C1 correction is made, errors will be able to be corrected as usual except in the nth line but, in case the C2 correction is made, all the data in the respective lines will be erroneous, the error correction will be impossible to carry out and, as a result, this sector will be unable to be read out.
As shown in FIG. 1, in the ordinary sector format, the byte synchronizing patterns are inserted into the data at fixed intervals. Therefore, if only the first byte synchronizing pattern can be correctly detected, even if the subsequent byte synchronizing patterns fail to be detected, in consideration of the periodicity, a pseudo byte synchronizing pattern detecting signal will be produced and, if the data are demodulated by this signal, the data will be able to be correctly read out.
However, as described above, in the conventional data recording and reproducing apparatus, there are problems that, in case the first byte synchronizing pattern can not be detected due to the influence of a dust or flaw, the reference point of the periodicity will not be able to be obtained, therefore no pseudo byte synchronizing pattern detecting signal will be able to be produced and, even if there is no error in any other part of the sector, it will be impossible to read out this sector.