Method for recording (sending) /reproducing (receiving) data, apparatus thereof and data recording medium

A C2 encoder encodes data of 24 symbols supplied from a two-symbol delaying/scrambling circuit and generates a Q parity of four symbols. Data and Q parity are supplied to a interleaving circuit. The interleaving circuit adds delays that vary for a unit delay amount D each as in 0, D, 2D, . . . , and so forth to individual symbols so as to interleave the data. In this case, since D=7, the maximum delay amount becomes 7.times.27=189. Thus, the total interleave length becomes 190. The total interleave length is slightly smaller than twice the unit of sub codes (98 frames). A C1 encoder encodes 28 symbols that have been interleaved and generates a P parity of four symbols.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a method for recording/reproducing 
(sending/receiving) data as a modification of a CD (compact disc) or the 
like, an apparatus thereof, and a data record medium thereof. 
2. Description of the Related Art 
Audio CDS (CD-DAs) that digitally and optically record audio signals are 
well known. A CD-DA has a diameter of for example 12 cm and a storage 
capacity of 600 MB or more. Thus, the CD-DAs can be used for external 
record mediums for computers as well as audio units. 
CD-ROMs that record digital data other than audio data in an audio data 
record region of the CD-DA have been standardized. The CD-ROMs are 
read-only record mediums. For the CD-ROMs, the same recording/reproducing 
processes as those of the CD-DAs are performed. In other words, digital 
data that has been error-correction-code encoded by the CIRC (Cross 
Interleave Reed-Solomon Code) encoding process as a folding type dual code 
encoding process and that has been modulated by the EFM (Eight to Fourteen 
Modulation) method is recorded on the CD-ROMs. 
In the folding type dual code encoding process, 24 symbols (bytes) of 12 
words are encoded with the Reed-Solomon code (C2 code) and thereby a 
parity of four symbols (Q parity) is generated. An interleaving process is 
performed for the data of 28 symbols and the Q parity. The resultant data 
is encoded with the Reed-Solomon code (C1 code) and thereby a parity of 
four symbols (P parity) is generated. A total of 32 symbols that are data 
of 24 symbols, Q parity of four symbols, P parity of four symbols, and a 
sub code of one symbol are sent as one frame. 
A sub code is composed of eight channels P to W. One symbol (one byte) 
composed of eight bit of the channels is placed in each frame. One unit is 
composed of sub codes for 98 frames. For example, the channels P and Q of 
each sub code are used for detecting the top position of a program. The 
other channels are used to record a still picture and character data. The 
access unit of the CD-ROM is 2,352 bytes (=24 bytes.times.98) that are 
data contained in 98 frames that are the unit of sub codes. This access 
unit is also referred to as a block. However, in the following 
description, the access unit is referred to as a sector. 
In the interleaving process of the CD-DA, 28 symbols are delayed with an 
amount that varies by a unit delay amount one after the other such as 0, 
D, 2D, . . . , and 27D (where D is the unit delay amount, D=four frames). 
Thus, the maximum delay amount is (4.times.27=108 frames). A frame is a 
block of data of 28 symbols that are encoded with the C1 code. Now, the 
total frame length between the symbol with the delay amount of 0 and the 
symbol with the maximum delay amount (27D) is referred to as the total 
interleave length (thus, 4.times.27+1=109 frames). Consequently, to 
correct an error, data of 109 frames should be read. 
The total interleave length defines the correction performance against a 
burst error of which errors sequentially take place in data due to a 
finger print on the disc, a scratch thereon, and so forth. The strength of 
the correction performance against the burst error is proportional to the 
total interleave length. Unlike with audio data, computer data cannot be 
interpolated. Thus, when computer data is used, the total interleave 
length is preferably increased. 
In addition, as in the above-described CD-ROMs, it is defined that one 
sector is composed of 98 frames. Thus, the size of one sector does not 
accord with the total interleave length. On the other hand, data is 
recorded and reproduced, sector by sector. Consequently, to rewrite or 
read data of one sector, data of adjacent sectors should be also read. 
Thus, data is wastefully accessed. 
OBJECTS AND SUMMARY OF THE INVENTION 
Therefore, an object of the present invention is to provide a method for 
recording/reproducing (sending/receiving) data of which the relation 
between the length of the unit of sub codes and the total interleave 
length is defined so as to improve the correction performance against a 
burst error and thereby preventing data from being wastefully accessed. 
The invention of claim 1 is a data recording apparatus for recording a 
predetermined number of frames on a record medium at a time, one frame 
being composed of information data and a sub-code corresponding to the 
information data, additional information corresponding to a predetermined 
number of frames being composed of a predetermined number of sub-codes, 
the data recording apparatus comprising: interleaving means for 
interleaving each of the frames with an interleave length that is a 
multiple of the predetermined number and forming interleaved frames; 
encoding means for encoding the interleaved frames with an error encoding 
code and for forming encoded interleaved digital data; and recording means 
for recording the encoded interleaved frames on the record medium. 
The invention of claim 2 is a data reproducing apparatus for reproducing 
data from a record medium on which a predetermined number of encoded 
interleaved frames have been recorded, the encoded interleaved frames 
being generated by interleaving and encoding frames, one frame being 
composed of information data and a sub-code corresponding to the 
information data, additional information corresponding to a predetermined 
number of frames being composed of a predetermined number of sub-codes, 
the data recording apparatus comprising: reproducing means for reproducing 
the encoded interleaved frames from the record medium and outputting the 
encoded interleaved frames; decoding means for decoding the encoded 
interleaved frames so as to form interleaved frames; and deinterleaving 
means for deinterleaving the interleaved frames with an interleave length 
that is a multiple of the predetermined number and for forming frames. 
The invention is claim 3 is a data recording method for recording a 
predetermined number of frames on a record medium at a time, one frame 
being composed of information data and a sub-code corresponding to the 
information data, additional information corresponding to a predetermined 
number of frames being composed of a predetermined number of sub-codes, 
the data recording method comprising the steps of: interleaving each of 
the frames with an interleave length that is a multiple of the 
predetermined number and forming interleaved frames; encoding the 
interleaved frames with an error encoding code and for forming encoded 
interleaved digital data; and recording the encoded interleaved frames on 
the record medium. 
The invention is claim 4 is a data reproducing method for reproducing data 
from a record medium on which a predetermined number of encoded 
interleaved frames have been recorded, the encoded interleaved frames 
being generated by interleaving and encoding frames, one frame being 
composed of information data and a sub-code corresponding to the 
information data, additional information corresponding to a predetermined 
number of frames being composed of a predetermined number of sub-codes, 
the data reproducing method comprising the steps of: reproducing the 
encoded interleaved frames from the record medium and outputting the 
encoded interleaved frames; decoding the encoded interleaved frames so as 
to form interleaved frames; and deinterleaving the interleaved frames with 
an interleave length that is a multiple of the predetermined number and 
for forming frames. 
The invention of claim 16 is a record medium for recording two or more 
units of a predetermined number of frames on a record medium at a time, 
one frame being composed of information data and a sub-code corresponding 
to the information data, additional information corresponding to a 
predetermined number of frames being composed of a predetermined number of 
sub-codes, each of the frames with an interleave length that is equal to 
or smaller than a multiple of the predetermined number being interleaved 
so as to form interleaved frames, the interleaved frames being encoded 
with an error encoding code so as to form first encoded interleaved 
digital data, the first encoded interleaved frames being recorded on the 
record medium, each of the frames with an interleave length that is larger 
than a multiple of the predetermined number being interleaved so as to 
form interleaved frames, the interleaved frames being encoded with an 
error encoding code so as to form second encoded interleaved digital data, 
the second encoded interleaved frames being recorded on the record medium. 
The above, and other, objects, features and advantage of the present 
invention will become readily apparent from the following detailed 
description thereof which is to be read in connection with the 
accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Next, an embodiment of the present invention will be described. FIG. 1 
shows the structure of a recording side according to an embodiment of the 
present invention. In FIG. 1, a disc 1 can record data. More practically, 
the disc 1 is a master disc for use with a CD-ROM mastering system, a 
read-once type CD (CD-WO), an erasable CD (CD-E), or the like. As an 
example, in this embodiment, a CD-ROM mastering system will be considered. 
Data to be recorded (referred to as record data) is supplied from a host 
computer 2 to a CD-ROM formatting circuit 4 through an interface 3. The 
formatting circuit 4 formats digital data as the record data corresponding 
to a CD-ROM format. As the CD-ROM format, mode 0, 1, 2, or the like is 
used. 
The output data of the CD-ROM formatting circuit 4 is supplied to a CD 
format encoder 5 (denoted by a dot-lined box in the drawing). The encoder 
5 is composed of a RAM 6, an interleaving circuit 7, a P parity, Q parity 
generating circuit 8, and an EFM modulating circuit 9 so as to generate 
record data in the same format as that of a CD-DA. As will be described 
later, the RAM 6, the interleaving circuit 7, and the parity generating 
circuit 8 perform a CIRC encoding process. The interleaving process is 
performed by controlling a write address and a read address of data 
to/from the RAM 6. The record data is supplied from the EFM modulating 
circuit 9 to an optical pickup 10 through a drive circuit (not shown). The 
optical pickup 10 records data on the disc 1 that is rotated by a spindle 
motor 11 at CLV (Constant Linear Velocity). In addition, a system 
controller 12 is disposed. The system controller 12 controls the 
formatting circuit 4, the CD format encoder 5, the optical pickup 10, and 
the spindle motor 11. 
With the disc 1 as a master disc, a CD-ROM is produced by the same 
duplicating process as that of a CD. FIG. 2 shows a structure for 
reproducing this CDROM. In FIG. 2, reference numeral 21 is the CD-ROM. A 
spindle motor 22 rotates the CD-ROM 21 at CLV. An optical pickup 23 reads 
data of the CD-ROM 21. A servo circuit 24 is disposed for controlling the 
optical pickup 23. The servo circuit 24 includes a focus servo that 
controls the focus of the optical pickup, a tracking servo that controls 
the tracking thereof, and a positioning servo that controls the radius 
position of the disc. 
Data that was reproduced (hereinafter referred to as reproduction data) is 
supplied from the optical pickup 23 to an EFM demodulating circuit 26 of a 
CD format decoder 25 (denoted by a dot-lined box in the drawing). A CLV 
controlling circuit 27 is disposed for controlling the EFM demodulating 
circuit 26. The CLV controlling circuit 27 controls a spindle motor 22 so 
that it rotates at CLV. The output data of the EFM demodulating circuit 26 
is supplied to a deinterleaving and interpolating circuit 28. In 
association with the deinterleaving and interpolating circuit 28, a RAM 29 
and an error correcting circuit 30 are disposed. As will be described 
later, the deinterleaving process is the reverse process of the 
interleaving process that is performed on the recording side. In other 
words, the deinterleaving process is a process for canceling a delay added 
to each symbol. By controlling a write address and a read address to/from 
the RAM 29, the deinterleaving process is accomplished. The interpolating 
process is a process for substituting an error symbol (that cannot be 
corrected) with the average of symbols that just follow and just precede 
in the time sequence. 
Reproduction data that has been error corrected is supplied from the CD 
decoder 25 to a sync, header detecting circuit 32 of a CD-ROM deformatting 
circuit 31 (denoted by a dot-lined box in the drawing). The sync, header 
detecting circuit 32 separates a sync (sync signal) and a header from each 
sector of the record data on the CD-ROM. The circuit 32 performs a 
descrambling process that is the reverse process of the scrambling process 
performed on the recording side. 
The header detecting circuit 32 is connected to a RAM controller 34 and an 
error correction and system manager 35. The RAM controller 34 controls a 
write operation and a read operation of the RAM 33. The error correction 
and system manager 35 detects an error for each sector, decodes an error 
correction code, and controls the operation of the deformatting circuit 
31. User data is supplied from the RAM controller 34 to a host computer 38 
through an interface 36. Likewise, an address, an error flag, and so forth 
are supplied from the error correction and system manager 35 to the host 
computer 38 through the interface 36. In addition, a system controller 37 
is disposed. The system controller 37 controls the CD-ROM decoder 25 and 
the CD-ROM deformatting circuit on the reproducing side. 
In addition to the recording/reproducing apparatus, the present invention 
can be applied for the case of which data is transmitted to a 
communication path. In this case, on the sending side, the output data of 
the EFM modulating circuit 9 is supplied to a modem. On the receiving 
side, the demodulated output data of the modem is supplied to the EFM 
demodulating circuit 26. 
FIG. 3A shows data structure of one frame of a CD-DA of which data has not 
been FFM modulated. On the disc, data that has been EFM modulated and a 
frame sync has been added is recorded. As shown in FIG. 3A, one frame is 
composed of data bits (24 symbols) (of which audio data is sampled with 16 
bits, left audio data and right audio data each being equivalent to six 
samples), a Q parity (four symbols), a P parity (four symbols), and a sub 
code (one symbol). One symbol is composed of the half of 16 bits, namely 
eight bits. 
Each frame recorded on the disc is composed of: 
______________________________________ 
Frame sync 24 channel bits 
Data bit 14 .times. 24 = 336 channel bits 
Sub code 14 channel bits 
Parity 14 .times. 8 = 112 channel bits 
Margin bits 3 .times. 34 = 102 channel bits 
______________________________________ 
Thus, the number of the total channel bits of one frame is 588 channel 
bits. 
The sub code (one symbol) of each frame includes one bit of each of eight 
channels P to W. As shown in FIG. 3B, one sector is composed of data of 
one unit of sub codes (namely, 98 frames). The first two sub codes of the 
98 frames are sub code frame syncs S and S.sub.1. 
FIG. 4 shows an outline of a CIRC encoding process performed by the CD 
format encoder 5. FIG. 5 shows a detail of the CIRC encoding process. 
FIGS. 4 and 5 are block diagrams that successively show steps of the 
encoding process. In the description for the CIRC encoding/decoding 
process, for simplicity, it is assumed that audio data is encoded. 24 
symbols of which one word of an audio signal is divided into high order 
eight bits and low order eight bits (W.sub.12 n,A, W.sub.12 n,B, . . . , 
W.sub.12n+11,A, and W.sub.12n+11,B where high order eight bits are denoted 
by A and low order eight bits are denoted by B) are supplied to a 
two-symbol delaying circuit/scrambling circuit 41. The two-symbol delaying 
process is performed for even-word data L.sub.6n, R.sub.6n, L.sub.6n+2, 
R.sub.6n+2, . . . , and so forth. Thus, even if an error takes place in 
all a sequence encoded by a C2 encoder 42, the error of the sequence can 
be interpolated. The scrambling process is performed for obtaining the 
maximum burst error interpolating length. 
The output data of the two-symbol delaying circuit/scrambling circuit 41 is 
supplied to the C2 encoder 42. The C2 encoder 42 performs a (28, 24, 5) 
Reed-Solomon code encoding process on GF(2.sup.8) and generates four Q 
parity symbols Q.sub.12n , Q.sub.12n+1, Q.sub.12+2, and Q.sub.12n+3. 
28 symbols as the output data of the C2 encoder 42 are supplied to an 
interleaving circuit 43. The interleaving circuit 43 adds delay amounts 0, 
D, 2D, . . . and so forth (that vary corresponding to the relation of an 
arithmetic sequence and that D is a unit delay amount) to the individual 
symbols so as to convert a first array of the symbols to a second array. 
In the conventional CD-DA format, D is four frames. Thus, adjacent symbols 
are spaced by four frames. The interleaving circuit 43 disperses a burst 
error. The maximum delay amount is 27D (=108 frames). The total interleave 
length is 109 frames. As will be described later, the total interleave 
length is allocated to a multiple of 98 frames or a value slightly smaller 
than the multiple thereof. 
The output data of the interleaving circuit 43 is supplied to a C1 encoder 
44. The C1 encoder 44 performs a (32, 28, 5) Reed-Solomon code encoding 
process on GF(2.sup.8) and generates four P parity symbols P.sub.12n, 
P.sub.12n+1, P.sub.12n+2, and P.sub.12n+3. The minimum length of each of 
the C1 code and the C2 code is five. Thus, a two-symbol error can be 
corrected. In addition, (provided that the positions of error symbols are 
known), a four-symbol error can be erased for a correction. 
32 symbols as the output data of the C1 encoder 44 are supplied to a 
one-symbol delaying circuit 45. The one-symbol delaying circuit 45 
separates adjacent symbols from each other so as to prevent a two-symbol 
error due to an error of a symbol or an error at the boundary of adjacent 
symbols from taking place. The Q parity symbols are inverted. Thus, even 
if all data symbols and parity symbols become zero, an error can be 
detected. 
FIG. 6 shows an outline of the CIRC decoding process performed by the CD 
format decoder 25. FIG. 7 shows a detail of the CIRC decoding process. 
FIGS. 6 and 7 are block diagrams that successively show steps of the 
decoding process. The decoding process is the reverse process of the 
encoding process. First, reproduction data is supplied from an EFM 
demodulating circuit 26 to a one-symbol delaying circuit 51. The 
one-symbol delaying circuit 51 cancels delays of symbols added in the 
one-symbol delaying circuit on the encoding side. 
32 symbols as the output data of the one-symbol delaying circuit 51 are 
supplied to a C1 decoder 52. The output data of the C1 decoder 52 is 
supplied to a deinterleaving circuit 53. The deinterleaving circuit 53 
adds delay amounts 27D, 26D, . . . , D, and 0 (that vary corresponding to 
the relation of an arithmetic sequence) to the individual 28 symbols so as 
to cancel the delay amounts added by the interleaving circuit 43. 
The output data of the deinterleaving circuit 53 is supplied to a C2 
decoder 54. The C2 decoder 54 decodes the C2 code. 24 symbols as the 
output data of the C2 decoder 54 are supplied to a two-symbol delaying 
circuit/descrambling circuit 55. The circuit 55 outputs decoded data of 24 
symbols. In FIG. 7, an error flag (not shown) generated by the C1 decoder 
52 is deinterleaved as with data symbols and supplied to the C2 decoder 
54. An interpolation flag generating circuit 56 generates an interpolation 
flag with the error flags supplied from the C1 decoder 52 and the C2 
decoder 54. With this interpolation flag, data that represents an error is 
interpolated. 
In the CD-ROM format, instead of 12 words (24 symbols) of the 
above-described audio samples, digital data (computer data, still picture 
data, text data, and so forth) are used. In the CD-ROM format, one sector 
is composed of 98 frames (2,352 bytes) that are one unit of sub codes. 
FIG. 8 shows the data structure of one sector in for example the mode 1 of 
the CD-ROM format. 
At the top of one sector, a synchronous signal of 12 bytes is placed. 
Thereafter, a header of four bytes is placed. The three bytes of the 
header represent a sector address (minute, second, and sector). The 
remaining bit of the header represents a mode. The sector address is a 
value that has a predetermined offset against an address contained in the 
Q channel of a sub code. The header is followed by user data of 2,048 
bytes. Auxiliary data of 288 bytes is added to the user data of 2,048 
bytes. The auxiliary data is composed of an error detection code (four 
bytes) for user data, a space (eight bytes), and a parity (276 bytes) for 
the error correction code. 
Next, the interleaving process as a feature of the present invention will 
be described. As shown in FIG. 9, the total interleave length of each of 
the conventional CD-DA format and the conventional CD-ROM format is 109 
(=108+1) frames. Thus, in FIG. 9, data at the sector m is placed as 
hatched lines. When the data at the sector m denoted by the hatched lines 
is rewritten, all the C1 sequence at the sector (m+1) and part of the C1 
sequence at the sector (m+2) are affected. In addition, all the C1 
sequence at the sector (m-1) and part of the C1 sequence at the sector 
(m-2) are affected. Thus, when the data at the sector m is rewritten, the 
parities of the C1 sequences at the sectors (m+1), (m+2), (m-1), and (m-2) 
should be changed. 
On the other hand, when data at the sector m is decoded and then 
reproduced, part of data at the sector (m-2), all data at the sector 
(m-1), all data at the sector (m+1), and part of data at the sector (m+2) 
are required along with all data at the sector m. Since the minimum unit 
of data being reproduced is a sector, data of five sector should be read. 
Thus, sectors that are not required should be wastefully read along with a 
required sector. 
FIG. 10 shows an example of an interleaving process according to the 
present invention. In this example, the total interleave length is equal 
to 98 frames. This total interleave length cannot be accomplished by an 
interleaving circuit that adds delays that vary by the unit delay amount D 
to individual symbols. Instead, by adding delay amounts of frames (0, 4, 
7, 11, 14, 18, 21, 25, 28, 32, 35, 39, 42, 46, 49, 53, 56, 60, 63, 67, 70, 
74, 77, 81, 84, 88, 91, and 95) to individual symbols, the total 
interleave length becomes equal to 96 frames. In this example, three 
frames and four frames are alternately allocated as the difference of 
delay amounts between adjacent symbols. 
In the interleaving process shown in FIG. 10, when one sector n is 
rewritten, after the sector n is read until it is decoded, sectors that 
are affected are only the sectors (n-1), n, and (n+1). Thus, the number of 
sectors to be accessed can be reduced and thereby data can be accessed at 
high speed. 
FIG. 11 shows another example of the interleaving process according to the 
present invention. In the example shown in FIG. 11, the unit delay amount 
D is allocated to seven. In the interleaving circuit 43 shown in FIG. 5, 
the minimum delay amount is 0. The maximum delay amount is (27.times.7=189 
frames). The total delay amount is 190 frames. The total interleave length 
is slightly smaller than twice the unit of sub codes (98 frames). 
In the interleaving process shown in FIG. 11, when one sector n is 
rewritten, the C1 parities of the C1 code sequences at the sectors (n+2), 
(n-1), (n+1), and (n+2) should be changed along with that at the sector n. 
Likewise, when the data at the sector n is decoded, the sectors (n+2), 
(n-1), n, (n+1), and (n+2) are required. That is the same as numbers of 
the sector required for the interleaving process of the conventional CD-DA 
and CD-ROM as shown in FIG. 9. However, the total interleave length is as 
large as 190 frames. Thus, the protection against a burst error can be 
enhanced comparing with the conventional method. 
In addition, according to the present invention, an interleaving process 
can be performed with D=14 or D=28. In this case, the total interleave 
lengths of these cases are (27.times.14+1=379&lt;98.times.4) and 
(27.times.28+1=757&lt;98.times.8), respectively. In each case, the total 
interleave length becomes slightly smaller than a multiple of the unit of 
sub codes. 
As described above, when the interleaving process of which the total 
interleave length is nearly a multiple of 98 frames where the multiple is 
larger than 2 is performed, the correction performance against a burst 
error can be improved. In addition, with a modulo (a multiple of 98) 
against the delay amount for the interleaving process and the 
deinterleaving process, the sector completion type encoding process can be 
easily accomplished. In the sector completion type interleaving process, 
diagonal lines that connect C2 code sequences fold back at multiples of 98 
frames. When the maximum delay amount is smaller than the unit of sub 
codes (for example, 196 frames) by nearly the unit delay amount (for 
example, 7-1=6), no folding deterioration takes place. Thus, the sector 
completion type encoding process can be properly performed. In this case, 
as in 28.times.7=196=98.times.2, 28.times.14=392=98.times.4, and 
28.times.28=784=98.times.8, the relation of multiples of 98 frames can be 
accomplished. 
In this embodiment, the total interleave length is allocated to a value 
slightly smaller than a multiple of 98 frames. However, part of the delay 
amounts may be increased so that the total interleave length becomes a 
multiple of 98 frames. In addition, according to the present invention, 
data of which the folding type dual code encoding process including the 
interleaving process with the total interleave length of 109 frames has 
been performed as in the conventional CD-DA format, CD-ROM format, and so 
forth or data of which the folding type dual code encoding process 
including the interleaving process with the total interleave length 
according to the present invention has been performed may be selected 
corresponding to the type of data or the like. Moreover, although the 
folding type dual code encoding process including the interleaving process 
with the total interleave length according to the present invention is 
performed, data may be recorded corresponding to the total interleave 
length being selected. 
The total interleave length can be selected corresponding to the record 
density of the record medium, the transmission rate of the transmission 
path, the type of the record data, and so forth. When the record density 
is high, since the length of a burst a error caused by the same defect on 
the record medium is long, the total interleave length is preferably long. 
On the other hand, when a large amount of data is sequentially accessed as 
in audio data and picture data, the conventional interleaving process can 
be used without a problem. 
Next, another embodiment of the present invention will be described in 
detail. In the present invention, data of which two types of interleaving 
processes have been performed is present on the same record medium or on 
the same transmission path. For example, with a unit of an area, a track, 
or a sector, data of which the two types of interleaving processes have 
been performed is present on the same disc. 
FIG. 12 is a block diagram showing the structure of the recording side of 
another embodiment of the present invention. In FIG. 12, for simplicity, 
similar portions to those in FIG. 1 are denoted by similar reference 
numerals and their description is omitted. 
An encoder 65 is composed of a RAM 66, a first interleaving circuit 67, a 
second interleaving circuit 69, a switching circuit 64, a P/Q parity 
generating circuit 68, and an EEM modulating circuit 70. The encoder 65 
generates record data in the same format as the CD-DA. 
The RAM 66, the first interleaving circuit 67, and the parity generating 
circuit 68 perform the above-described CIRC encoding process. The 
interleaving process is performed with a first interleave length by 
controlling a write address and a read address of the RAM 66. 
Likewise, the RAM 66, the second interleaving circuit 67, and the parity 
generating circuit 68 perform the CIRC encoding process. The interleaving 
process is performed with a second interleave length by controlling a 
write address and a read address of the RAM 66. 
The output data of the first interleaving circuit 67 or the output data of 
the second interleaving circuit 69 is selected by the switching circuit 
64. 
An ID that represents one of the first interleave length and the second 
interleave length is supplied from the host computer 2 to the switching 
circuit 64 through the interface 3, the CD-ROM formatting circuit 4, and 
the system controller 12. 
In this case, the ID for identifying the interleave length should be 
recorded on the tape along with data. More practically, the ID is recorded 
at the header of each sector of the data structure of the CD-ROM. 
The selected output data is EFM modulated by the EFM modulating circuit 70 
and supplied to the optical pickup 10. 
Next, with reference to FIG. 13, the structure of the reproducing side of 
this embodiment will be described. For simplicity, in FIG. 12, similar 
portions to those in FIG. 2 are denoted by similar reference numerals and 
their description is omitted. 
Data reproduced from an optical pickup 23 is supplied to an EFM 
demodulating circuit 28 of a CD format decoder 75 denoted by dotted lines 
of FIG. 13 through a waveform shaping circuit (not shown). 
The output data of the EFM demodulating circuit 26 is supplied to a first 
deinterleaving/interpolating circuit 73 and a second 
deinterleaving/interpolating circuit 78. 
In association with the first deinterleaving/ interpolating circuit 73 and 
the second deinterleaving/ interpolating circuit 78, a RAM 79 and an error 
correcting circuit 74 are disposed. 
As described above, the first deinterleaving process and the second 
deinterleaving process are reverse processes performed on the recording 
side. In other words, in the first deinterleaving process and the second 
deinterleaving process, delays applied to symbols are canceled. The 
deinterleaving processes are performed by controlling a write address and 
a read address of the RAM 79. Each of the interpolating processes corrects 
an un-correctable error of a symbol with the average of the preceding and 
following symbols on the time axis. 
The output data of the first deinterleaving/interpolating circuit 73 and 
the output data of the second deinterleaving/interpolating circuit 78 are 
input to the switching circuit 72. 
The switching circuit 72 selects the output data of the first 
deinterleaving/interpolating circuit 73 or the output data of the second 
deinterleaving/interpolating circuit 78 corresponding to the ID for 
identifying the interleave length. The ID is recorded at the header of 
each sector in the data structure of the CD-ROM. The ID is input to the 
switching circuit 72 through the EFM demodulating circuit 26 and the 
system controller 37. 
The reproduced data selected by the switching circuit 72 is supplied to a 
sync/header detecting circuit 32 of a CD-ROM deformatting circuit 31 
denoted by dotted lines of FIG. 13. The sync/header detecting circuit 32 
performs the above-described process. 
In the above-described embodiments, a structure of which data that has been 
interleaved with two types of interleave lengths is recorded/reproduced. 
However, the present invention can be applied for a structure of which 
data that has been interleaved with three or more types of interleave 
lengths is recorded/reproduced. 
Moreover, the present invention can be applied for the case that a 
semiconductor memory is used as a record medium as well as the 
above-described disc-shaped record mediums. 
According to the present invention, since the relation of the unit of sub 
codes and the total interleave length is defined, data that is accessed 
can be used without a loss. In addition, according to the present 
invention, the total interleave length can increased so as to improve the 
correction performance against a burst error. Moreover, according to the 
present invention, when the total interleave length is allocated to a 
multiple of the unit of sub codes, hardware resources of encoders and 
decoders in the conventional CD format and software resources thereof can 
be used. In addition, the total interleave length can be changed and the 
sector completion type encoding process can be easily accomplished. 
Moreover, data with different interleave lengths can be recorded on the 
same record medium and data can be easily reproduced therefrom. 
Having described specific preferred embodiments of the present invention 
with reference to the accompanying drawings, it is to be understood that 
the invention is not limited to those precise embodiments, and that 
various changes and modifications may be effected therein by one skilled 
in the art without departing from the scope or the spirit of the invention 
as defined in the appended claims.