Note: Descriptions are shown in the official language in which they were submitted.
3~)
DATA TRANSMISSION METHOD SUITABLE FOR A DISC
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates generally to a data
transmission method, and more particularly to a method
of this kind which is suitable for transmitting blocks
of data, each of which comprises a predetermined
quantity of data, to a transmission path, for example,
on a disc-shaped recording medium such as a magneto-
optical disc, in the form of a track which is dividedinto a plurality of sectors into which the blocks of
data are respecti~ely written or recorded.
Description of the Prior Art
It is known to add an error correcting code and an
error detecting code to data to be transmitted so as to
detect and correct errors occurring in the data while
the data is transmitted through a transmission path (or
a recordin~ medium). In this technique, the error
correcting code (ECC), e.g., a b-adjacent code, for
correcting errors occurring in a predetermined quantity
of data to be transmitted i5 first produced and then
added to the predetermined guantity of data. Next, the
error detecting code (EDC) is produced on the basis of
the error correcting code and the predetermined quantity
of data to be transmitted. Then, the data with the
error correcting code and the error detecting code is
transmitted to the transmission path (or the recording
medium). The data with the error correcting code and
the error detecting code received through the
transmission path is processed to correct a possible
error thereof which may occur in the transmitted dataO
To ~e specific, by the use of the error detecting code,
it is first detected whether or not a possible error
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exists in the received data and the error correcting
code is added thereto. If it is detected that any error
exists in the above data, the error in the transmitted
data is corrected by the use of the error correcting
code. That is, the error detecting code of the data is
used to check the error before the error correcting
process of the received data. Further, there is a
product code which is also used to correct a possible
error in data. This product code is to produce an error
correcting code for each row and column of data of a
rectangular array comprising a predetermined quantity of
data. A known code, e.g., Reed~Solomon code, is
employed as the error correcting code thus produc~d.
These data and error correcting codes are successively
transmitted in a predetermined order to the transmission
path. The predetermined quantity of data with the error
correcting code received through the transmission path
is again arranged into a rectangular array. Then, the
possible errors in the data are corrected by the use of
the error correcting codes generated for each of the
data in the row and column directions.
However, according to the prior art, the above-
mentioned rectangular array of product code is
constructed for only one kind of a recording medium.
Therefore, if the data is to be recorded on a plurality
of different types of recording media, each of which has
a different data capacity, the data processing procedure
cannot be commonly utilized for different kinds of
recording media which constitutes a great inconvenience
in the data processing.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is the object of the present
invention to provide a data transmission method which
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can be commonly utilized when data is recorded on a
plurality of kinds of recording media.
To achieve the above object, the present invention
provides a data transmission method for data formed as a
S rectangular array comprising a block of data formed of n
words, supplementary data associated with said block of
data and an error detecting code for detecting possible
errors which may occur in said block of data and said
supplementary data. The method comprises the steps of:
producing and adding a first error correcting
code for and to each row of data of the rectangular
array in which n words of data are sequentially
arranged;
producing and adding a second error correcting
code for and to each column of data of the
rectangular array in which words of data are
written to thereby ~orm a product-coded data from
the block of data, the supplementary data, the
first error correcting code and the second error
correcting code;
fetching and transmitting the product-coded
data along the rows of the array;
when the block o~ data is changed in word
number from the number n to a number _, varying the
number of data words in the column direction of the
rectangular array in response to the above change
while keeping the number of data words in the row
direction fixed so as to form a new rectangular
array to comport with the increase in the quantity
of data; and
sequentially fetching and transmitting the new
product-coded data forming the new rectangular
array along the row direction.
The above and other objects, features and advan-
tages of the present invention will become apparent from
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the following detailed description of the preferred
embodiment taken in conjunction with the accompanying
drawings, throughout which like reference numerals
designate like elements and parts.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. lA is a diagram showing a first example of the
construction of a product code according to the present
invention;
Fig. lB is a diagram showing a modification of Fig.
lA in which the quantity of data to be transmitted is
different from that shown in Fig. lA;
Fig. 2A is a diagram showing a second example of
the construction of a pxoduct code according to the
present invention;
Fi~. 2B is a diagram showing a modification of Fig.
2A in which the quantity of data to be transmitted is
different from that shown in Fig. 2A:
Fig. 2C is a diagram showing a modification of Fig.
2B;
Fig. 3 is a diagram showing a sector format in the
case where the product coded data according to the
invention is recorded in each sector of a disc-shaped
recording medium; and
Fig. 4 is a block diagram showing the construction
of an apparatus for recording and reproducing the
product-coded data on a disc-shaped recording medium,
according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
This invention provides a data transmission method
in which a product code is formed for blocks of data and
the product-coded data is successively transmitted via a
transmission path. The method is suitable for the case
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where the quantity of data forming the above block of
data may be varied and then transmitted.
Disc-shaped recording media are used for data
storage for computers. The disc-shaped recordiny media
can be provided with one spiral track or a plurality of
cylindrical tracks, the track or tracks being divided
into a plurality o~ sectors. Examples o~ this kind of
recording media are floppy discs, magnet~-optical discs,
worm (write once read many) discs, and so on.
Fig. 3 shows an example of a sector format for a
magneto-optical disc. Referring to Fig. 3, a track 12
formed on a magneto-optical disc 11 is divided into a
plurality of sectors in its circumferential direction,
on each of which is recorded a predetermined quantity of
data with an error correcting code ECC, an error
detecting code EDC and so on.
As shown in Fig. 3A, one track comprises ~n+1)
sectors. In this embodiment, one track is formed of 32
sectors.
A format of data to be recorded on one sector is
arranged, for example, as shown in Fig. 3B. To be
specific, each sector comprises a header portion, a data
portion, and gap portions GAP provided behind each of
the header portion and the data portion.
At the head of the header portion, preamble data
are recorded and following the header portion there are
twice recorded an address signal ADD, comprising track
address data TA and sector address da~a SA, ~ollowed by
an error correcting code ECC and an address
synchronizing signal ASYNC.
Further, in the data portion, there are recorded at
the head, preamble data and data added with an error
correcting code ECC and so on to be transmitted.
In general, 512 bytes of usable data are recorded
in one sector in the track formed on a floppy disc.
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However, other media, e.g., a magneto-optical disc, worm
disc, or the like, from which data is optically
reproduced, have a much larger data capacity than that
of the floppy disc. For such mass data storage media,
the capacity of one sector, i.e., the quantity of data
which can be recorded in one sector, can be considered
as set at a product value obtained by multiplying 512-
bytes by a certain integer, ~.g., 1024 (e.gn, 512 X 2)
bytes, in plac~ of 512-bytes.
The present invention provides a data transmission
method suitable for the case where data is ~ransmitted
to more than two different kinds of media which have
different sector capacities set, respectively, at 512
bytes and a product value obtained by multiplying S12
bytes by a certain integer.
Figs. lA and lB are drawings showing examples of
the construction of the product codes.
In Fig. lA, 512-bytes of serial data Do ~ D511 form
a block of data to be transmitted (or recorded). There
is provided supplementary data SUPD having a length of
12-bytes which is required to transmit the 512-bytes of
data. The supplementary data SUPD comprises information
relative to the data to be transmitted (or recorded),
e.g., in~ormation indicative of whether the data is to
be processed by, for example, a computer, or is to be
processed in real time such as audio signals,
information indicative of a data transmission rate,
information indicative of the destination of the data,
information indicative of data allocation, i.e., track
numb2r, sector number, and so on, when the data is to be
recorded on a disc-shaped recording medium, and
information about the link between respective sectors.
Further, there is provided an error detecting code EDC
formed of 4 bytes, e.g. a cyclic redundancy code CRC for
detecting possible errors which may occur in the block
3LX81~3~t
of 512-bytes of data to be transmitted and the
supplementary data SUPD formed of 12-bytes. Then, the
512-bytes of data to be transmitted, the 12-bytes of
supplementary data SUPD, and the 4-bytes of error
detecting code are rearranged in the digital memory of
the transmitting apparatus (not shown) into the form of
a rectangular array which has a 33-byte length in the
row direction and a 16-byte length in the column
direction. A first error correcting code Cl, e.g., (37,
33) Reed-Solomon code is produced and added to each 33-
bytes of data in the row direction. And a second error
correcting code C2, e.g., (20, 16) Reed-Solomon code is
produced and added to each 16-bytes of data in the
column direction. Thus, a product code is form~d. The
product coded-data comprising 740 (37 X 20) bytes is
fetched from memory and transmitted to or recorded in
each sector of a disc-shaped recording medium beginning
with the data located at the first column and the first
row and successively along the row direction, in the
form of serial data. The 740-bytes of serial data thus
transmitted or recorded is again transformed into the
original product code. Then, possible errors introduced
into the product code during transmission are corrected
in the row direction and in the column direction,
respectively, by the use of a Cl parity and a C2 parity,
that is, first and second error correcting codes C1 and
- C2. Next, the 512-bytes of data and the 12-bytes of
supplementary data SUPD which are subjected to error
correction by the use of the C1 and the C2 parities are
finally checked by the use of the error detecting code
EDC to determine whether or not the data contains
possible errors.
Fig. lB shows the construction of a product code
when the capacity of one block of data to be transmitted
is increased from 512 bytes to 1024 (512 X 2) bytes. It
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will be assumed that product-coded data having 1332 (37
X 36) bytes is recorded, e.g., in each sector of the
track, on a disc-shaped recording medium.
The present invention deals with this increase of
data contained in one block by changing the number of
data words in a direction different from the sequential
order in which the data is written in the rectangular
array. To be specific, in Fig. lB, the number of data
in the column direction of the rectangular array is
increased from 16-bytes to 32-bytes to cope with the
above data increase. The product code shown in Fig. lB
is composed by stacking in memory two 528-byte
rectangular arrays of Fig. lA, each comprising 512-bytes
of data, 12-bytes of supplementary data SUPD, and 4-
bytes of error detecting code EDC, and the errorcorrecting codes C1 and C2' are produced and added to
each of the rows and columns of data, respectively, of
the stacked rectangular array.
As shown in Fig. lB, for the C1 parity, the same
~37, 33) Reed-Solomon code is used whi~h was used for
the array of Fig. lA, and for the C2' parity, a t36, 32)
Reed Solomon code is used. Each of 12-bytes of
supplementary data SUPD contains information indicative
of the quantity of data contained in one block to be
transmitted (102~-bytes), information indicative of
which of the two blocks each of the 512-bytes of data is
located in, information indicative of the transmission
rate of the data, and so on.
Figs. 2A to 2C show the construction of product
codes in which the supplementary data SUPD in the
examples of Figs. lA and lB is placed after the data to
be transmitted, that is, in front of the error detecting
code EDC.
Referring to Fig. 2A, added after the 512-bytes of
data to be transmitted is the supplementary data SUPD
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having 12-bytes which is required to transmit the 512-
bytes of data. Further, the 4-bytes of error detecting
code EDC, such as cyclic redundancy code CRC, for
detecting possible errors in the 512-bytes of data and
the supplementary data SUPD of 12-bytes is produced and
added to the above-mentioned data. The 528-bytes of
data is formed into a rectanyular array which has a 48-
byte length in the row direction and an ll-byte length
in the column direction. Then, a Cl parity having 4-
bytes, e.g., a (52, 4~3) Reed-Solomon code, is produced
and added to each row of 48-bytes of data of the
rectangular array. Also, a C2 parity having 2-bytes,
e.g., a (13, ~1) Reed-Solomon code, is produced and
added to each ll-bytes of data arranged in the column
direction of the rectangular array. Data in the product
code thus constructed is successively fetched and
transmitted from the first column, first row along the
row direction.
Fig. 2B shows the construction of a product code in
which one block of data to be transmitted in Fig. 2A is
increased from 512-bytes to 1024 (512 X 2) bytes. As is
clear from Fig. 2~, a second block of 512-bytes of data
is placed after a first block of 512-bytes of data.
Placed after the second block of 512-bytes of data are
the 12-bytes of supplementary data SUPD and the error
detecting code EDC for the first block of data followed
by the SUPD and ~DC for the second block of data, to
thereby form a rectangular array having 1056 (48 X 22)
bytes of data. Next, in the same manner as shown in
Fig. lA, a C1 parity, e.g., a (52, 48) Reed-Solomon
code, is produced and added to each row of the
rectangular array of the 48 bytes in the row direction.
Then, a C2 parity, e.g., a (24, 22) Reed-Solomon code,
is produced and added to each column of 22 data bytes of
the rectangular array~ Finally, a product code having
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1248 (52 x 24) bytes is thus produced. The data in the
product code is successively fetched and transmitted
beginning with the first column, first row and then
along the row direction.
Incidentally, in Fig. 2B, the 512-bytes of data is
taken as a fundamental unit and the 12-bytes of
supplementary data SUPD and the 4-bytes of error
detecting code EDC to be added to each block of the 512-
bytes of data are located close to each other after the
1024-bytes of data. However, in Fig. 2C, 1024-bytes of
data is specified as a fundamental unit and, for
example, 28-bytes of supplementary data SUPD and 4-
bytes of error detecting code EDC are produced to detect
the possible errors of the former. In this case, a
rectangular array having a 48 byte row length and a 22-
byte column length is produced. Therefore, in Fig. 2C
the numb~r of data words in the row direction is the
same as that of the rectangular array shown in Fig. 2A,
while the number of data words in the column direction
is increased. Note that the same Cl parity can be used
for each array.
Fig. 4 is a block diagram showing the construction
of a recording and reproducing apparatus for recording
the above described product-coded data on and
reproducing the same from a disc-shaped recording
medium.
Reference numeral ll designates a magneto-optical
recording disc incIuding, e~g., a spiral-shaped track on
which the above data is recorded. A recording and
reproducing head (not shown) in the apparatus is
controlled such that the head correctly scans the
previously formed track.
Reference numeral 21 designates a disc driving
motor and the disc 11 is controlled by the driving motor
21 such that the disc 11 is rotated at a predetermined
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speed, i.e., at a constant angular velocity. The
driving motor 21 is provided with a frequency generator
22 which generates a frequency signal FG proportional to
the rotational speed of the driving motor 21. The
frequency signal FG is supplied to a phase comparator
circuit 23. The phase comparator circuit 23 is also
supplied with one of two speed reference signals REF
selected by a switch 26. Although this speed reference
signal REF can be varied according to the transmission
rate of data to be recorded or reproduced, as will later
be described in detail, on playback tPB) it has a
frequency equal to that of the output signal FG from the
frequency generator 22 when the disc 11 is rotated at a
desired rotational speed. The speed reference signal
REF can be substituted by a frequency signal which can
be obtained by dividing the frequency of the signal FG.
In this case the output signal FG should also be divided
by the same dividing ratio before being supplied to the
comparator circuit 23.
An output signal from the phase comparator circuit
23, i.e., the comparison result, is integrated by an
integrator circuit 24 to be a speed error signal
indicative of the difference betwaen the speed reference
signal and the actual rotational speed of the motor 21.
The signal is fed back to the motor 21 through a motor
drive 25 so that the motor 21 rotates at an angular
velocity corresponding to the speed reference signal
REF.
Reference is now made to a recording system
arranged in the apparatus according to the invention.
Reference numeral 3lD designates an input terminal to
which are inputted digital signals such as data from a
computer, time sampled analog data, for example, analog
audio data sampled at various predetermined sampling
frequencies with each value being sampled as one word
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made of a predetermined number of bits, digital data atvarious transmission rates of data, and so on.
Reference numeral 31A designates an input terminal to
which are supplied analog signals, e.g., audio signals.
Digital data inputted to the terminal 3lD are
supplied to a selector 33 while analog signals inputted
to the terminal 31A are first supplied ko an A/D
converter 32 to be converted into corresponding
digital signals. The sampling frequency of the A/D
converter 32 can be changed to various values, e.g., 32
kHz, 44.1 kHz, 48 kHz, and so on. Further, it is
possible that the sample can be selected from various
numbers of bits, e.g., 8-bits, 12-bits, 16-bits and so
on. In the case of such digitally converted analog
signals, particularly in the case of digitally
converted audio signals, the resulting signal has a
correlation among data words so that an erroneous word
can be interpolated by words located at the vicinity of
said erroneous word. This is because the changes in
amplitude of an analog signal are not as likely to be
abrupt as in the case of a digitally generated signal.
The digital signal from the A/D converter 32 is
supplied to the selector 33.
The selector 33 selects, by manual operation or a
control signal supplied thereto from an external
circuit (not shown), either the digital signals from
the input terminal 31D or the A/D converter 32. The
digital signal selected by the selector 33 is then
supplied to an ECC encoder 34, wherein the data are
transformed into a product-coded block of data (e.g.,
512-bytes) to be recorded in one sector on the track of
the disc-shaped recording medium 11 according to the
method heretofore described. The data processed by the
ECC encoder 34 is supplied to recording means 35 to be
adequately modulated. The output of the recording
means is supplied to the head as serial data and is
then recorded on the magneto-optical disc 11.
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At that time, the rotational speed of the disc 11
is controlled so as to be synchronized with the
transmission rate of the digital data to be recorded.
The switch 26 is changed over to a REC terminal side so
that the speed reference signal generated from a speed
reference signal generator circuit 36 is supplied to the
phase comparator circuit 23 as the speed reference
signal REF~
If data to be recorded is the digital signal from
the input terminal 31D and if the data is self-clocking
data, the data from the input terminal 31D is supplied
to the speed reference signal generator circuit 36,
wherein a clock signal is extracted from the data, the
transmission rate is calculated on the basis of the
clock signal, and a speed reference signal corresponding
to the transmission rate calculated is generated by the -
circuit 36~
On the other hand, if data from the input terminal
31D is not self-clocking data, that is, if a signal
indicative of the transmission rate of the data, e.g~, a
clock signal is separately sent from the data, the
signal indicative of the transmission rate is supplied
through an input terminal 31R to the speed reference
signal generator circuit 36 which generates a speed
reference signal corresponding to the transmission rate
obtained from the signal indicative of the transmission
rate~
If the data to be recorded is an analog signal
inputted from the input terminal 3lA and converted into
digital data by the A/D converter 32, a switch 37 is
changed over according to the aforementioned sampling
frequency and the bit number of one word length is
selected, so that a speed reference signal corresponding
to the transmission rate is generated by the speed
reference signal generator circuit 36.
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Assume, for example, that non-self-clocking,
digital signal having a known transmission rate is
inputted to the terminal 3lD but the signal indicative
of the transmission rate is not transmitted. In this
case a speed reference signal corresponding to the known
transmission rate can be selected by the switch 37.
The motor 21 is driven in a manner such that the
phase (frequency) of the speed reference signal
corresponding to the transmission rate of the inputted
data and that of the frequency signal generated by the
frequency generator 22 coincide with each other, and
thereby the disc 11 is rotated at a rotational speed in
- synchronism with the transmission rate of the inputted
data.
The signal indicative of the transmission rate of
the data from the signal generator circuit 36 is
supplied to the ECC encoder 34 and then recorded on the
disc 11 as a portion of the supplementary data SUPD.
Also recorded as a portion of the supplemen~tary data
SUPD are the sampling fre~ency and the bit number
forming one word length of the data.
If an ECC-encoded digital signal with parity and
other redundancy bits is inputted to the terminal 3lD,
it is necessary to decode the signal to make it only
inherent digital data.
The data indicative of the transmission rate of the
- recorded data may be recorded in a directory area which
is allocated in the most inner track or the most outer
track of the disc.
Next, a reproducing system of the apparatus
according to the invention will be hereinafter described
with reference to Fig. 4.
The digital signal reproduced from the disc 11 by
an optical reproducing head (not shown) is supplied to a
reproducing means 41 to be demodulated. The digital
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signal from the reproducing means 41 is then supplied to
a supplementary data decoder 46 wherein the signal
indicative of the transmission rate, recorded in the
supplementary data area of each sector, is decoded. A
speed reference signal generator circuit 47 is now
supplied with the decoded signal indicative of the
transmission rate, allowing a corresponding speed
reference signal to be generated. The speed reference
signal in turn is supplied to the phase comparator
circuit 23 through a playback terminal side PB of the
switch 26. Thus, the disc 11 is rotated at a rotational
speed in synchronism with the transmission ratP of the
recorded data.
The speed reference signal for controlling the
rotation of the disc upon playback or reproduction can
be generated by previously reading, prior to the data
reproduction, the data indicative of the transmission
rate which is recorded in the directory area of the
disc. Moreover, if the transmission rate recorded on
the disc is known by a memory or the like, it is of
course possible to manually change tne spePd reference
signal.
The data thus reproduced from the disc rotating at
a rotational speed in synchronism with the data
transmission rate is supplied to an ECC decoder 42
through the reproducing means ~1. The ECC decoder
carries out error correction and so on for each sector
and then makes the data only inherent data, i.e., with
redundancy data removed. If the reproduced data thus
processed is digital data, the data is delivered to an
output terminal 45D by a multiplexer 43. On the other
hand, if the reproduced data is digital data converted
from an analog signal, the data is supplied to a D/A
converter 44 to be reconverted into an analog signal
before being delivered to an output terminal 45A.
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The data required to effect D/A conversion, e.g.,
the sampling frequency and the bit number of one word of
data in the D/A converter 44, can be previously known by
decoding the supplementary data or reading the data
recorded in the directory area. The D/A conversion in
response to this known data can then be effected.
In this embodiment, the driving motor 21, i~e., the
rotation of the disc 11, is controlled to rotate at a
constan~ angular velocity. However, the above described
technique can be applied to the case where the driving
motor 21 is conkrolled to rotate the disc 11 at a
constant linear velocity.
As described above, when the size of a block
containing data to be transmitted is varied, the present
invention adjusts to this variation in the block size by
altering the number of data words in one direction (in
the column direction) of the rectangular array while
keeping the number of data words in the other direction
(in the row direction) the same. According to this
method, although different sizes of blocXs are to be
transmitted, these blocks are reformed into blocks
containiny the same quantity of data and some of the
same error correcting codes (Cl parity) are generated
for each reformed block. It is therefore possible to
utilize in common the same hardware, such as the Cl
error code gènerator, when different sized blocks of
data are to be transmitted. Also, when the transmitted
data are decoded, it is possible to commonly utilize an
error correcting process in which possible errors
occurring in the transmitted data are corrected by the
use of the same error correcting codes (Cl parity).
Further, while in all of the above examples the
number of data words has been increased, it should be
apparent that the reverse process is also possible
~5 utilizing the teachings of the invention. Thus, an
1~8~
array of 1056-bytes of data (Fig. lB) can be reformed as
two 740-byte arrays (Fig. lA).
The above description is given on a single
preferred embodiment of the invention, but it will be
apparent that many modifications and variations coul~ be
effected by one skilled in the art without departing
from the spirit or scope of the novel concepts of the
invention so that tha scope of the invention should be
determined by the appended claims only.
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