JPH02203477A - Data reproducing method for optical recording medium - Google Patents

Abstract

PURPOSE:To decide the quality of the write data with a simple circuit constitution by correcting the erasion in a normal read state and performing no correction of data in a read state which is set right after a writing operation. CONSTITUTION:An optical card 1 includes plural tracks 2 extending in the lengthwise direction of the card 1 in parallel with each other in the card width direction. The data on a sector of each track 2 includes the information data 11, a check word 12 of a 1st code series (C1 code series), and a check word 13 of a 2nd code series (C2 code series). In a normal read state the erasion is corrected with higher correcting ability and no correction is given to the erasion in a read state set right after a writing operation. then a normal error correction is carried out based on an error position detected by a syndrome arithmetic. Thus it is possible to strictly check the write data obtained right after a writing operation in a simple way just by adding some change to the decoding algorithm at a normal reproduction state. Then the reliability is more improved for the written data.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for reproducing data from an optical recording medium.

[Conventional technology]

Conventionally, when writing data to an optical recording medium such as an optical card, the data is read immediately after writing to check whether it was written correctly or not, and if it is not written correctly, an alternative data area is secured and the data is written there. Writing is generally performed again.

By the way, compared to magnetic recording media, optical recording media have
Generally, since the error rate is high, strong error correction encoding is applied to the data to be written so that errors can be sufficiently corrected at the expected error rate of the recording medium, and error correction is performed during reading. However, since the recording medium changes over time, the error rate increases as time passes from immediately after recording. Therefore, in Japanese Patent Application Laid-Open No. 62-88176, even if the error is within the correctable range immediately after recording,
In order to prevent the error rate from deteriorating due to subsequent changes over time and becoming uncorrectable during subsequent reading, a flag indicating the number of errors that have occurred in the error correction code is counted, and the count value is A system has been proposed in which if the value exceeds a predetermined value, it is determined that the write is defective and the data is rewritten.

[Problem to be solved by the invention]

However, in the recording and reproducing apparatus disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 62-88176, there is no means for generating a flag indicating the number of errors occurring in the error correction code, which is unnecessary in normal reproduction. Since a means for counting the flag is required, the circuit configuration becomes complicated and the decoding algorithm becomes complicated.

This invention was made by focusing on the above-mentioned problems.
Without changing the decoding algorithm during normal playback,
Therefore, it is an object of the present invention to provide a data reproducing method for an optical recording medium that can determine the acceptability of written data with a simple circuit configuration.

[Means and operations for solving the problem] In order to achieve the above object, the present invention includes information words arranged in a matrix, a check word of a first error correction code in a first direction, and a check word of the first error correction code in a first direction. The data written on the optical recording medium is read by adding a check word of the second error correction code in a second direction different from the first direction, and the read data is added to the check word of the second error correction code in a second direction different from the first direction. In decoding using the check word and the check word of the second error correction code, erasure correction is performed during normal reading, and erasure correction is not performed during reading immediately after writing.

In this way, during normal readout, erasure correction with higher correction ability is performed, and during readout immediately after writing, normal error correction is performed based on the error position by syndrome calculation without using erasure correction, so that during normal playback, By just making a slight change to the decoding algorithm, written data can be easily and strictly checked immediately after writing, and the reliability of written data can be further improved.

〔Example〕

The present invention will be described below with reference to the case where an optical card is used as the optical recording medium. FIG. 1 shows the configuration of an example of an optical card. This optical card 1 is formed by forming a plurality of tracks 2 extending in the card longitudinal direction and parallel to the card width direction. FIG. 2 shows an example of the data structure of one sector within the trunk 2. As shown in FIG. 111 is information data, 12 is a check word of the first code sequence (hereinafter referred to as ci code sequence), and 13 is a check word of the second code sequence (hereinafter referred to as ci code sequence).
This is called a 2-code sequence. ) is the test word. In this example, up to two errors can be corrected in each code word in both the CI and C2 code series, and furthermore, in the C2 code series, up to four errors can be corrected by performing erasure correction. Note that when performing error correction on a medium with a high raw error rate, such as an optical card, erasure correction is usually performed in order to further improve the correction ability. The l sector data shown in FIG. 2 is generated as follows.

■ (MXN) pieces of information data, DI, 1, D2
゜1, -..., DM, l, 01.2, ・
Arrange them in a matrix in the order of...

■ One row of data blocks arranged in a matrix (
Dl, 1 , D2.1 , ...-1 Kano, 1) is subjected to C2 encoding and C2 test data (PL, 1 ,
..., PI, 4) and repeat this sequentially N times for each column.

■ One row of data block generated by C2 encoding (D
l, 1, Dl, 2, -・-1Di, N) vs.
C1 encoding is performed and C1 check data (Ql, 1, Ql
, 4) and sequentially apply this to each row M+4)
Repeat times.

In the manner described above, one sector of write data can be generated. Writing this data is usually done in the second
The data is sequentially read and executed from the first row to the (M+4)th row in the figure.

FIG. 3 shows the configuration of essential parts of an example of an optical card recording/reproducing apparatus embodying the present invention. The optical card 1 is attached to a predetermined position on a conveyor belt 22 that is passed between pulleys 21a and 21b, and is driven by a motor 2 by a motor drive circuit 23.
4, the optical card 1 is transported back and forth in the track direction. The optical head 25 projects writing light or reading light from the diode 25a onto the optical card 1 via the optical system 25b, and the reflected light is transmitted to the detector 25.
It is configured so that it is incident on c. Detector 25c
The output of controller 26 is supplied to controller 26.
After being demodulated and converted into a read data signal within 6, it is temporarily stored in the RAM 27a in the error correction circuit 27.

The output of the detector 25c is also supplied to the focus/track servo circuit 28, where a focus error signal and a track error signal are detected, thereby driving the optical head 25 in the focusing and tracking directions to drive the optical card 25. The incident light is controlled so that it always follows the track in a focused state. The controller 26 controls a laser drive circuit 29, a motor drive circuit 23, a focus/track servo circuit 28, and an error correction circuit 27.
L. When recording data, it operates to error-correct encode data from a host computer (not shown), perform modulation, and write to a desired track of the optical card L. When reproducing data, the optical card 1 reads data on a desired track of the optical card 1, performs demodulation, and then transfers the error-corrected reproduced data to a host computer (not shown).

Next, the operation of the error correction circuit 27 will be explained. When recording data, first, data from the host computer is temporarily stored in the RAM 27a via the controller 26. After that, the interleave address generation circuit 27c
RAM2 according to the interleaved address generated by
Data is read out from 7a in an order suitable for error correction encoding and sent to the encoding/decoding circuit 27b, where it is subjected to error correction encoding and then stored again in the RAM 27a. After all the data in the data is processed, the data is sent to the controller 26 again and the error correction encoding is completed. When reproducing data, error correction is performed using the same procedure as when recording data. That is, first, read data demodulated within the controller 26 is temporarily stored in the RAM 27a. After that, the interleave address generation circuit 27c
RAM2 according to the interleaved address generated by
Data is read from 7a in an order suitable for error correction and sent to the encoding/decoding circuit 27b, where error correction is performed and then stored in the RAM 27a again. After the above processing is performed on all data in the RAM 27a, the data is sent to the controller 26 again and decoding is completed.

FIG. 4 is a flowchart showing the decoding operation of one sector worth of data shown in FIG. 2, which is executed by the error correction circuit 27 shown in FIG. First, normal error correction is performed on the code word of the 01 code series in the first row of FIG. 2 based on the error position obtained by syndrome calculation (step 1), and it is checked whether the result is uncorrectable. (Step 2). If the error is not uncorrectable, c
Check whether error correction has been completed for all code words of one code series (step 3). If there are still more, the code word pointer is incremented by 1 (step 4) and the process returns to step 1. If the error cannot be corrected in step 2, it is checked whether the currently executed decoding is checking the written data immediately after writing (step 5). As a result, if the write data is checked immediately after writing, the process directly proceeds to step 3. Otherwise, it is regarded as normal decoding, and an erasure flag for erasure correction is set in that line (step 6), and the process proceeds to step 3.

The above is the decoding operation for the CI code sequence. When the error correction of the CI code sequence is completed in step 3, the process proceeds to step 7, and then the decoding for the c2 code sequence begins.

First, for the code word of the 02 code series in the first column of Figure 2,
Ordinary error correction is performed based on the error position obtained by syndrome calculation (step 7). Check whether the result is an uncorrectable error or not (step 8).
If error correction is not possible, check whether error correction has been completed for all codewords of the c2 code series (step 9); if not yet, increment the codeword pointer by 1 (step 1o) and return to step 7. . When the error correction of the 02 code series is completed in step 9, it is assumed that the error correction has been successfully performed for the target sector, and the decoding is terminated. If the error cannot be corrected in step 8, it is checked whether the decoding currently being performed is checking the write data immediately after writing (step 11). As a result, if it is checking the write data immediately after writing, the target 02
The codeword is flagged as uncorrectable (
Step 12''), at that point the sector is considered uncorrectable and the decoding is terminated.

If not, check whether the number of erasure flags set during decoding of the CI code sequence is within the erasure correction range (step 13), and if it is within the erasure correction range, the number of erasure flags set during decoding of the CI code sequence is Erasure correction is performed on the data (step 14) and the process proceeds to step 9. If it is not within the erasure correction range, the target C2 code word is determined to be uncorrectable and an uncorrectable flag is set (step 12), and at that point, the sector is determined to be uncorrectable and decoding is terminated.

This completes the decoding of one sector. Here, the quality of the written data immediately after writing is determined based on the uncorrectable flag. That is, when the uncorrectable flag is set, it is determined that the writing is defective, and when the uncorrectable flag is not set, it is determined that the writing is good.

Note that in the above example, if even one codeword in the C2 code series is uncorrectable, decoding for that sector is finished at that point, but even if there is an uncorrectable codeword, decoding is still performed for all codewords. It may also be possible to determine whether the sector is uncorrectable based on whether the uncorrectable flag is set at that time.

〔Effect of the invention〕

As described above, according to the present invention, in normal reading, erasure correction with higher correction ability is performed, and in reading immediately after writing, normal error correction is performed based on the error position by syndrome calculation without using erasure correction. By making a slight change to the decoding algorithm during normal playback, it is possible to easily and strictly check the written data during read-after-write, further improving the reliability of the written data. It becomes possible to do so.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of an optical card as an optical recording medium used in the present invention, Fig. 2 is a diagram showing an example of the data structure of one sector of the track shown in Fig. 1, and Fig. 3 is a diagram showing an example of the data structure of one sector of the track shown in Fig. 1. FIG. 4 is a flowchart showing a decoding operation executed by the error correction circuit shown in FIG. 3. 1... Optical card 2... Track 11.
...Information data 12...Test word 13 of C1 code series...Test word 21a, 21b of C2 code series...Pulley 22...Transport belt 23...Motor drive circuit 24...Motor 25 ...Optical head 25a...Laser diode 25b...Optical system 2
5c...Detector 26...Controller 27...Error correction circuit 27a...RAM2
7b... Encoding/decoding circuit 27c... Interleave address generation circuit 2B...
- Focus/track servo circuit 29...laser drive circuit.

Claims (1)

[Claims] 1. A check word of a first error correction code in a first direction and a check word of a second error correction code in a second direction different from the first direction in information words arranged in a matrix. When reading the data written on the optical recording medium by adding , and decoding the read data using the check word of the first error correction code and the check word of the second error correction code, normally 1. A method for reproducing data from an optical recording medium, characterized in that erasure correction is performed when reading data, but erasure correction is not performed when reading immediately after writing.