W88113C Datasheet, PDF (91/102 Pages) Winbond – ATAPI CD-ROM DECODER & CONTROLLER

W88113C
5.4 Decoder Logic
5.4.1 Sync Detection/Insertion
The sync field of CD-ROM data is recorded as following: 1 (00h) bytes, 10 (FFh) bytes and 1 (00h)
byte. This sync field is detected for sector synchronization if SDEN (0Bh.w6) is enabled. To prevent
loss of synchronization caused by broken sync, an internal counter can provide inserted sync signal if
SIEN (0Bh.7) is enabled. There are no sync bytes in CD-DA format, so SDEN (0Bh.w6) should not be
set.
5.4.2 Descramble
Bytes 12 to 2351 of each CD-ROM sector is scrambled in decoding. Setting DSCREN (0Bh.5) high
enables the descramble logic. Descramble logic should be disabled while reading of CD-DA data.
5.4.3 Disk-Monitor Mode
The decoder logic is in disk-monitor mode if CTRL0 (0Ah,w) is set as 80h. In disc-monitor mode, no
ECC correction and EDC checking is carried. The sector ready interrupt flag SRIb (01h.r5) is
immediately generated when the header bytes are available in HEAD0-3 (04h-07h,r). The header
bytes in disc-monitor mode are less trustworthy than that in buffer-correction mode.
5.4.4 Parallel ECC Correction
The error correction encoding/decoding of the CD-ROM sector is carried by a Reed-Solomon
Product-Like Code (RSPC). The RSPC is a product code over GF(2⁸) field which is generated by the
primitive polynomial
P(x) = x⁸ + x⁴ + x³ + x² + 1
The primitive element α of GF(2⁸) is
α = (00000010)
where the right-most bit is the least significant bit.
The data is divided into high byte plane and low byte plane before decoding. The RSPC decoding,
operating on bytes, is then applied twice, once to the high byte plane, once to the low byte plane.
To improve the efficiency of RSPC decoding, a parallel ECC correction logic is implemented on chip.
After sync detection and descrambling, the parallel ECC correction is carried on high byte plane and
low byte plane simultaneously. This correction scheme is about 33% faster than conventional
decoder.
The Q-code correction and P-code correction are enabled by QCEN (0Ah.w1) and PCEN (0Ah.w0)
respectively. If both correction operations are enabled, Q-code correction is executed first. The
corrected data are written back to external RAM if CWEN (0Bh.w4) is high.
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Publication Release Date: Mar. 1999
Revision 0.61