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Section 23 CD-ROM Decoder
R01UH0134EJ0400 Rev. 4.00 Page 1191 of 2108
Sep 24, 2014
SH7262 Group, SH7264 Group
Section 23 CD-ROM Decoder
The CD-ROM decoder decodes streams of data transferred from the CD-DSP. When the medium
is CD-DA*
1
, the data stream is not input to the CD-ROM decoder because it consists of PCM data.
In the case of CD-ROM*
2
, the stream of data is input and the CD-ROM decoder performs sync
code detection and maintenance, descrambling, ECC correction, and EDC checking, and outputs
the resulting stream of data.
However, since the stream received by the CD-ROM decoder is assumed to consist of data from a
CD-ROM transferred via the serial sound interface, the decoder does not bother with the subcodes
defined in the CD-DA standard.
Notes: 1. Compliant with JIS S 8605 (Red Book)
2. Compliant with JIS X 6281 (Yellow Book)
23.1 Features
Sync-code detection and maintenance
Detects sync codes from the CD-ROM and is capable of providing sync-code maintenance
(automatic interpolation of sync codes) when the sync code cannot be detected because of
defects such as scratches on the disc.
Five sector-synchronization modes are supported: automatic sync maintenance mode, external
sync mode, interpolated sync mode, and interpolated sync plus external sync mode.
Descrambling
ECC support
P-parity-based correction, Q-parity-based correction, PQ correction, and QP correction are
available.
PQ correction and QP correction can be applied repeatedly up to three times. This, however,
depends on the speed of the CD. For example, three iterations are possible when the CD-ROM
decoder is operating at 60 MHz with a double-speed CD drive.
Two buffers are provided due to the need for ECC correction. This allows parallel operation,
where ECC correction is performed in one buffer while the data stream is being received in the
other.
EDC checking
The EDC is checked before and after correction based on the ECC. Furthermore, an operating
mode is available in which, if the result of pre-correction EDC checking indicates no errors,
ECC correction is not performed regardless of the result of syndrome calculation.