CD subcode transfer system for transferring correct Q subcodes

Details CD subcode transfer system for transferring correct Q subcodes CD subcode transfer system for transferring correct Q subcodes

2000-03-15

2003-02-11

Hindi, Nabil (Department: 2753)

Dynamic information storage or retrieval

Control of storage or retrieval operation by a control...

Control of information signal processing channel

C369S047210, C369S059230

Reexamination Certificate

active

06519216

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a system (referred to as subcode transfer system) for transferring correct subcodes of a compact disk (CD) to a digital audio interface (I/F) for outputting retrieved digital CD signals.
BACKGROUND OF THE INVENTION
CD signals contain a set of 8 bit symbols called subcoding symbols, one set for each data frame in addition to synchronization signals and digital audio signals.
A block of 98 such data frames constitutes a unified frame, which is a unit for subcoding CD signals.
Included in the subcoding symbols are 8 bit symbols P, Q, R, S, T, U, V, and W. Symbols P and Q are used to search for a starting bit of a melody and an execution of a programmed operation. Symbols R through W are provided for such special functions as displaying still pictures and Kara-Oke characters on a screen.
The data retrieved from a CD is mostly demodulated and converted to analog audio signals for analog audio devices, but the demodulated signals may be output also in the digital form for use with a digital device such as an MD. For better use of the digital signals, it is necessary to attach to the digital signals appropriate subcodes.
As an example, Q channel data may be utilized in processing different requests such as a request to replay a movement of a melody as instructed by a program, and a request to display elapsed time in the movement or absolute time.
FIG. 1
shows a major portion of a conventional subcode transfer system, in which demodulated digital audio signals of a CD are output to an MD together with subcodes attached thereto to make better use of the digital signals.
As shown in
FIG. 1
, the system includes a subcode I/F block
61
which consists of a subcode buffer
62
, a register
63
, and a control circuit
64
. First, a subcode is extracted from a given block of CD data, which subcode is stored in the subcode buffer
62
. At the same time, a cyclic redundancy code (CRC) check bit included in the Q channel data of the subcode is checked to determine if the Q channel data as a whole is correct or not. The result of the CRC check is registered in the register
63
as status information of the Q channel data. This status information in the register
63
is supplied to the control circuit
64
, and if the Q channel data stored in the subcode buffer
62
is correct, the subcode is transferred from the subcode I/F block
61
to the digital audio I/F block
65
through the control circuit
64
.
The subcode transferred from the subcode I/F block
61
to the digital audio I/F block
65
is stored in a subcode buffer
66
. The subcode is then attached to the digital audio signal (not shown) as the digital audio signal is output to an external device such as MD.
In conventional CD subcode transfer systems, the subcode is transferred unless the CRC check bit is determined to be incorrect. That is, the subcode is transferred based solely on the CRC check. However, since the CRC check coding is a rather simple error detection coding, its error can be overlooked, especially in cases where many errors are involved in the data retrieved from a CD.
Consequently, it is often the case that an erroneous subcode is determined to be correct. In that case, the erroneous subcode will be transferred. That means that if the time information is in error for example, it cannot be regenerated after it is copied on an MD for example, or, if it is regenerated, it causes an error displaying erroneous time or processing the data at wrong time.
It is therefore an object of the invention to provide an improved subcode transfer system in which only correct subcodes of a CD are transferred by checking not only their CRC check bits but also the subcodes themselves. The latter check can be made by noting the characteristics of the subcodes.
SUMMARY OF THE INVENTION
In one aspect of the invention, there is provided a CD subcode transfer system, including:
means for receiving a CD signal and outputting, along with a subcode, digital data derived from the CD signal after the digital data is error corrected and demodulated;
means for determining whether a CRC check bit for Q channel data of the subcode is correct and for determining whether the Q channel data is correct upon comparison of the Q channel data with preceding Q channel data; and
means for transferring the subcode and attaching the subcode to the digital data when the CRC check bit is determined to be correct and the Q channel data is determined to be correct.
In another aspect of the invention, there is provided a CD subcode transfer system, including:
CD signal processing means for receiving a CD signal and outputting, along with a subcode, digital data derived from the CD signal, error corrected, and demodulated;
a subcode I/F block for holding a current subcode contained in the CD signal supplied from the CD signal processing means and for holding a CRC check bit for Q channel data in a current subcode as status information;
a CPU block for retrieving at least current Q channel data and status information in the form of the CRC check bit, determining whether the CRC check bit is correct, and comparing the Q channel data with the preceding Q channel data to thereby determine whether the Q channel data is correct;
a digital I/F block for receiving the digital data and the subcode and for outputting the digital data with the subcode attached thereto, wherein
the subcode to be attached to the digital data is supplied to the digital I/F block only when both of the CRC check bit and the current Q channel data are determined to be correct.
A CD subcode transfer system of the invention may be adapted to supply the subcode to be attached to the digital data provided from the CD signal processing means, from the CPU block to the digital I/F block.
Alternatively, a CD subcode transfer system of the invention may be adapted to supply the subcode to be attached to the digital data provided from the CD signal processing means, from the subcode I/F block holding the subcode to the digital I/F block directly in response to a transfer instruction received from the CPU block.
In another aspect of the invention, there is provided a CD subcode transfer system, including:
a CD signal processor for receiving a CD signal and outputting, along with a subcode, digital data derived from the CD signal after the digital data is error corrected and demodulated;
a CPU block for determining whether a CRC check bit for Q channel data of the subcode is correct and for determining whether the Q channel data is correct upon comparison of the Q channel data with preceding Q channel data; and
a digital audio I/F block for receiving the subcode and attaching the subcode to the digital data when the CRC check bit is determined to be correct and the Q channel data is determined to be correct.
Since the CD subcode is transferred on condition that said CRC check bit and the Q channel data are both correct, the CD subcode transfer system stops the transfer of the subcode to the digital I/F block, even if the subcode has many errors and an incorrect determination is made that the CRC check bit is correct. Thus, the invention may stop the erroneous display of data due to incorrect subcodes and always provides only correct subcodes.
Since the subcode retrieved in the CPU is transferred from the CPU block to the digital I/F block, no further means is required.
It would be appreciated that the entire subcode may be directly transferred from the subcode I/F block to the digital I/F block based on a data transfer instruction issued by the CPU, thereby allowing a fast subcode transfer.


REFERENCES:
patent: 5237575 (1993-08-01), Maeda et al.
patent: 5471441 (1995-11-01), Nonaka et al.
patent: 5917782 (1999-06-01), Kim et al.
patent: 5931921 (1999-08-01), Kyle

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