JP3670758B2 - CD-ROM decoder - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a CD-ROM decoder that changes digital data read from a disk medium into a predetermined format and supplies the digital data to a computer device or the like.
[0002]
[Prior art]
In a CD player that reproduces a compact disc (CD), the rotation of the disc and the control of the pickup position with respect to the disc are performed so that the data recorded on the disc can be read at a constant speed. Since these controls are performed mechanically precisely, they are easily affected by vibration, and the pickup position may be shifted by slight vibration. When such a positional shift occurs, the continuity of data read from the disk is lost, and sound skip occurs in the audio signal generated based on the data. Therefore, a CD player for a specific application that often receives vibrations requires a so-called shock proof function that allows data to be continuously extracted even if the pickup position is shifted due to vibrations.
[0003]
FIG. 3 is a block diagram showing a configuration of an audio CD player having a shock proof function.
The CD pickup unit 1 receives the reflected light of the light irradiated on the disk 2 and extracts the intensity of the light as a change in voltage value. The pickup control unit 3 controls the pickup position of the CD pickup unit 1 with respect to the disc 2 so that the pickup unit 1 can read the data stored on the disc 2 in the correct order. The analog signal processing unit 4 reads a change in voltage value extracted by the CD pickup unit 1 and shapes the waveform to generate an EFM (Eight to Fourteen Modulation) signal. The digital signal processing unit 5 receives the EFM signal generated by the analog signal processing unit 4, performs signal processing based on a predetermined CD format such as EFM demodulation and CIRC (Cross-Interleave Reed-Solomon Code) decoding, and performs audio processing. Generate data. The shock proof control unit 6 receives the audio data generated by the digital signal processing unit 5, temporarily writes the audio data to the buffer RAM 7, and then continuously reads out the audio data at a constant cycle, and sends it to the next stage circuit. Supply. The audio data output from the shock proof control unit 6 is converted into an audio signal by a D / A conversion circuit and reproduced, for example. The control microcomputer 8 is composed of a one-chip microcomputer with a built-in memory, and controls the operation of each unit in accordance with a control program stored in the memory. At the same time, when it is detected that the pickup position of the CD pickup unit 1 has shifted, an instruction is given to the pickup control unit 3 to return the pickup position to the position before the shift. Thereby, the operation of each part is synchronized with each other so that the shock proof function operates correctly.
[0004]
FIG. 4 is a block diagram showing a configuration of the shock proof control unit 6.
The shock proof control unit 6 includes a DSP interface circuit 6a, a reproduction circuit 6b, and an address management circuit 6c. The DSP interface circuit 6 a interfaces with the digital signal processing unit 6, takes audio data output from the digital signal processing unit 6 sequentially, and writes it in the buffer RAM 7. The reproduction circuit 6b reads out and outputs the audio data stored in the buffer RAM 7 at a constant cycle. Then, the address management circuit 6c maintains the amount of audio data stored in the buffer RAM 7 within a certain range by managing the write address and the read address of the buffer RAM 7. That is, when the buffer RAM 7 is full, the control microcomputer 8 is instructed to stop reading data from the disk 2, and when the audio data stored in the buffer RAM 7 becomes smaller than a predetermined amount. An instruction is provided to resume reading data.
[0005]
The speed at which the CD pickup unit 1 reads data from the disk 2 is set to be several times the speed at which the reproduction circuit 6 c reads audio data from the buffer RAM 6. As a result, the data read from the disc 2 to the CD pickup unit 1 precedes the audio data output from the reproduction circuit 6c by the amount of data stored in the buffer RAM 6. Therefore, when the data read from the disc 2 becomes discontinuous due to the positional deviation of the CD pickup unit 1, the reading operation of the CD pickup unit 1 is stopped and control is performed so that the CD pickup unit 1 is returned to the correct position. Is called. Meanwhile, since the audio data is continuously read from the buffer RAM 7 by the reproduction circuit 6c, the audio data is output from the shock proof control unit 6 without interruption.
[0006]
[Problems to be solved by the invention]
By the way, in a CD-ROM system that utilizes a CD as a read-only memory (ROM) for a computer, there is an increasing demand for reproducing an audio CD. In addition, it is also considered that digital data for CD-ROM system and digital data for audio are stored on the same disk, and these data are read while being switched. Sharing with audio players is an issue.
[0007]
In the case of a normal CD-ROM system, compatibility from an audio CD player is maintained from data reading to EFM demodulation and CIRC decoding processing. Therefore, an audio disk is reproduced by the CD-ROM system. This can be easily realized by adding a D / A conversion circuit or the like.
However, when it is necessary to provide a shockproof function as described above, it is necessary to greatly increase the circuit scale. In particular, for the memory portion, several M bits are required for the error correction portion and the shock proof function portion of the CD-ROM system, which causes an increase in cost.
[0008]
Accordingly, an object of the present invention is to make it possible to reproduce an audio disc without skipping sound in a CD-ROM system while preventing an increase in circuit scale.
[0009]
[Means for Solving the Problems]
The present invention has been made in order to solve the above-described problems. The feature of the present invention is that the digital data read from the disk medium is subjected to correction processing of a code error included in the data, and the computer equipment side In a CD-ROM decoder that transfers data to a disk medium, an input interface circuit that captures digital data read from a disk medium and sequentially writes it in a memory circuit provided therein, and correction processing of a code error for the digital data written in the memory circuit An error correction circuit for performing the processing, an output interface circuit for reading the digital data from the memory circuit in response to an instruction from the computer device and transferring the digital data to the computer device, and reading the digital data from the memory circuit at a constant cycle. An audio playback circuit that outputs audio data; The provided, when the digital data read from the disk medium is associated with the audio information is to read the digital data written in the memory circuit from the input interface circuit directly to the audio reproduction circuit.
[0010]
According to the present invention, audio data and CD-ROM data are commonly taken into the input interface circuit and written to the memory circuit, the CD-ROM data is read from the memory circuit by the output interface, and the audio data is read by the reproduction circuit. As a result, a memory for storing CD-ROM data by error correction and a memory for storing audio data by shock proof control are commonly used. Therefore, it is possible to prevent the circuit scale from increasing.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing the configuration of a CD-ROM system employing a CD-ROM decoder of the present invention.
In the CD pickup unit 11, the pickup position with respect to the disc 12 is controlled by the pickup control unit 13, receives the reflected light from the disc 12, and extracts the intensity of the light as a change in voltage value. The analog signal processing unit 14 reads a change in the voltage value extracted from the CD pickup unit 11 and generates an EFM signal having 588 bits as one frame. As shown in FIG. 2, in the EFM signal, the 24 bits at the beginning of each frame are assigned to the synchronization signal, and then 14 bits are repeatedly assigned to the data bits with 3 connection bits interposed therebetween. The digital signal processing unit 15 takes in the EFM signal generated by the analog signal processing unit 14, performs EFM demodulation, and converts 14 bits into 8 bits as shown in FIG. In this EFM demodulation, 8-bit subcode data is extracted from the first data bit following the synchronization signal, and 32-byte symbol data is generated from the remaining data bits. Further, CIRC decoding is performed on the 32-byte symbol data to generate CD-ROM data of 24 bytes per frame or audio data of 12 words per frame. Here, in the case of CD-ROM data (mode 1), as shown in FIG. 3, a total of 2352 bytes of 24 bytes × 98 frames are handled as one block, a synchronization signal (12 bytes), a header (4 bytes), User data (2048 bytes), error detection code EDC (4 bits), and error correction code ECC (276 bytes) are respectively allocated. Further, the CD-ROM data is scrambled to 2340 bytes of the data of one block excluding the synchronization signal 12 bytes, and is descrambled at the time of reproduction to be returned to the original state.
[0012]
The CD-ROM decoder 16 includes a DSP interface circuit 16a, an error correction circuit 16b, a host interface circuit 16c, and a reproduction circuit 16d. The DSP interface circuit 16a forms an interface with the digital signal processing unit 15 and generates a system clock for detecting the synchronization signal of the captured data and determining the operation timing of each unit. Further, when the data input from the digital signal processing unit 15 is CD-ROM data, the descrambling process is performed to restore the original state, and then the data is written in the buffer RAM 17 connected to the CD-ROM decoder 16. If the data input from the digital signal processing unit 15 is audio data, it is written in the buffer RAM 17 as it is. The error correction circuit 16b takes in the CD-ROM data written in the buffer RAM 17 from the DSP interface circuit 16a for each block (98 frames), performs correction processing based on the error detection code EDC and the error correction code ECC, and performs the buffer RAM 17 Of the data stored in the data, the erroneous data is rewritten with correct data. The error correction circuit 16b stops operating when audio data is input from the digital signal processing unit 15. Then, the host interface circuit 16 c reads out the CD-ROM data subjected to the error correction processing by the error correction circuit 16 b from the buffer RAM 17 and outputs it to the host computer, takes in various commands from the host computer, and gives them to the control microcomputer 18. The reproduction circuit 16d continuously reads out audio data from the buffer RAM 17 at a constant cycle and outputs the audio data to the reproduction device including the D / A converter.
[0013]
The control microcomputer 18 sets the operation timing of each unit according to a built-in processing program, and controls so that data read from the disk 12 is processed correctly in any case. The control microcomputer 18 differs from the CD-ROM decoder 16 when handling CD-ROM data and when handling audio data, depending on the determination of the flag attached to the subcode data read by the digital signal processing unit 15. Execute the process. That is, when CD-ROM data is input from the digital signal processor 15, the DSP interface circuit 16a, the error correction circuit 16b, and the host interface circuit 16c are operated, and the input CD-ROM data is sequentially input to the buffer RAM 17. In addition to writing, the CD-ROM data is subjected to code error correction processing and then output to the host computer. At this time, the control microcomputer 18 responds to an instruction from the host computer side taken into the host interface circuit 16c, and picks up the control unit 13 so as to selectively take out the CD-ROM data stored at the target position of the disk 12. Give instructions to. As a result, the desired CD-ROM data is read from the disk 12, subjected to a second code error correction process by the CD-ROM decoder 16, and transferred to the host computer. On the other hand, when audio data is input from the digital signal processing unit 15 to the CD-ROM decoder 16, the DSP interface circuit 16a and the reproduction circuit 16d are operated to write the audio data sequentially into the buffer RAM 17 and to buffer the audio data. It is read out from the RAM 17 at a constant cycle and output. Here, the speed at which the CD pickup unit 11 reads data from the disk 12 is set to be several times the speed at which the playback circuit 16d reads audio data from the buffer RAM 17, and the audio data written from the DSP interface circuit 16a to the buffer RAM 17 is written. However, the audio data read from the buffer RAM 17 to the reproduction circuit 16d precedes the audio data stored in the buffer RAM 17. At this time, the control microcomputer 18 maintains the amount of audio data stored in the buffer RAM 7 within a certain range by managing the write address and the read address of the buffer RAM 17, and the data read by the CD pickup unit 11 is invalid. When it becomes continuous, reading is temporarily stopped, and an instruction is given to the pickup control unit 13 to return the CD pickup unit 11 to the correct position. Thereby, even when the pickup position of the CD pickup unit 11 is deviated and the data read from the disk 12 becomes discontinuous, it is possible to achieve a shock proof function for extracting audio data without interruption.
[0014]
In addition, since the time axis of audio data can be extended by using this shock proof function, even a disc in which digital data for CD-ROM system and digital data for audio are mixed in a CD-ROM system compatible with double speed. Can be easily reproduced. In the case of a CD-ROM system that supports double speed such as 8 × speed and 12 × speed that rotates the disk at several times the standard speed (for example, 8 times, 12 times, etc.), even if audio data is stored in the same disk Audio data cannot be played back at 8x speed or 12x speed. Therefore, it is necessary to switch the rotational speed of the disk, but switching between the rotational speed of 8 times or more and the standard rotational speed increases the burden on the spindle motor and the servo system control tends to become unstable. It is difficult to actually operate. Therefore, it is necessary to switch the rotation speed between the reading of the digital data for the CD-ROM system and the reading of the digital data for audio by using the time axis expansion process achieved by the shock proof function using the buffer RAM 17. Disappear. Therefore, the digital data for the CD-ROM system and the digital data for audio can be continuously read while maintaining the rotational speed of the disk at 8 × speed or 12 × speed.
[0015]
According to the CD-ROM decoder 16 described above, the buffer RAM 17 connected to the CD-ROM decoder 16 can be shared by the code error correction processing and the shock proof control. In the CD-ROM decoder 16, the code error correction process and the shock proof control are not performed simultaneously, so there is no need to increase the memory capacity. In normal operation, about 1 to 2 Mbits are required for the correction process of the code error and about 2 to 4 Mbits are required for the shock proof control. Therefore, a maximum of 4 Mbits is sufficient for the buffer RAM 17. is there.
[0016]
【The invention's effect】
According to the present invention, the DSP interface circuit is compatible with both audio data and CD-ROM data, and the host interface circuit and the reproduction circuit are provided in parallel to the buffer RAM, thereby connecting to the CD-ROM decoder. The buffer RAM can be used in common for correction of code errors for CD-ROM data and shockproof processing for audio data. Accordingly, it is possible to prevent an increase in the circuit scale of the peripheral circuit of the CD-ROM decoder having a shock proof function for reproducing audio data, and it is possible to suppress an increase in cost of the CD-ROM system.
[0017]
Also, even when playing a disc that contains a mix of digital data for CD-ROM systems and digital data for audio, it is not necessary to switch the rotational speed of the disc by reading both data. The burden on the driving spindle motor can be reduced. Further, since the servo control of the spindle motor can be simplified, the effect of cost reduction is great.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a CD-ROM system using a CD-ROM decoder of the present invention. FIG. 2 is a diagram showing a state of data read from a disk.
FIG. 3 is a diagram showing a format of CD-ROM data.
FIG. 4 is a block diagram showing a configuration of a conventional CD-ROM system.
FIG. 5 is a block diagram showing a configuration of a shock proof control unit.
[Explanation of symbols]
1, 11 CD pickup unit 2, 12 Disc 3, 13 Pickup control unit 4, 14 Analog signal processing unit 5, 15 Digital signal processing unit 6 Shockproof control unit 7, 17 Buffer RAM
8, 18 Control microcomputer 6a, 16a DSP interface circuit 6b, 16d Reproduction circuit 6c Address control circuit 16b Error correction circuit 16c Host interface circuit

Claims (4)

In a CD-ROM decoder that corrects a code error included in data and transfers the digital data read from the disk medium to the computer equipment side, the digital data read from the disk medium is captured and the memory circuit provided therewith An input interface circuit for sequentially writing, an error correction circuit for performing a code error correction process on the digital data written to the memory circuit, and the memory connected to the memory circuit and in response to an instruction from a computer device An output interface circuit that reads out the digital data from the circuit and transfers it to a computer device; and an audio reproduction circuit that is connected to the memory circuit and that reads out the digital data from the memory circuit at a constant period and outputs it as audio data. Provided with the above disk medium CD-ROM characterized in that when the digital data read out from is associated with audio information, the digital data written in the memory circuit is directly read out from the input interface circuit and supplied to the audio reproduction circuit decoder. When continuity is interrupted by digital data associated with audio information read from the disk medium and taken into the input interface circuit, it is stored in the memory circuit until the next continuous digital data is received. 2. The CD-ROM decoder according to claim 1, wherein the digital data is continuously read out to the audio reproduction circuit and the continuity of the audio data reproduced by the audio reproduction circuit is maintained. 2. The CD-ROM decoder according to claim 1, wherein one of the output interface circuit and the audio reproduction circuit is selectively operated, and the operation of the error correction circuit is stopped when the audio reproduction circuit is in operation. In a CD-ROM decoder that corrects a code error included in data and transfers the digital data read from the disk medium to the computer equipment side, the digital data read from the disk medium is captured and the memory circuit provided therewith An input interface circuit for sequentially writing, an error correction circuit for performing a code error correction process on the digital data written to the memory circuit, and the memory connected to the memory circuit and in response to an instruction from a computer device An output interface circuit that reads out the digital data from the circuit and transfers it to a computer device; and an audio reproduction circuit that is connected to the memory circuit and that reads out the digital data from the memory circuit at a constant period and outputs it as audio data. Provided with the above disk medium When the digital data read from the voice information is associated with the audio information, the digital data written in the memory circuit from the input interface circuit is read out in a cycle longer than the cycle at the time of writing, and the time axis is expanded. A CD-ROM decoder which is supplied to an audio reproduction circuit.

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