LC78624E Datasheet, PDF (24/27 Pages) Sanyo Semicon Device – Compact Disc Player DSP

LC78624E
24. Circuit Block Operating Descriptions
• RAM address control
The LC78624E incorporates an 8-bit × 2k-word RAM on chip. This RAM has an EFM demodulated data jitter handling
capacity of ±4 frames implemented using address control. The LC78624E continuously checks the remaining buffer
capacity and controls the data write address to fall in the center of the buffer capacity by making fine adjustments to the
frequency divisor in the PCK side of the CLV servo circuit. If the ±4 frame buffer capacity is exceeded, the LC78624E
forcibly sets the write address to the ±0 position. However, since the errors that occur due to this operation cannot be
handled with error flag processing, the IC applies muting to the output for a 128 frame period.
Position
–4 or less
–3
–2
–1
±0
+1
+2
+3
+4 or more
Division ratio or processing
Force to ±0
589
589
Increase ratio
589
588
Standard ratio
587
587
Decrease ratio
587
Force to ±0
• C1 and C2 Error Correction
The LC78624E writes EFM demodulated data to internal RAM to compensate for jitter and then performs the
following processing with uniform timing based on the crystal oscillator clock. First, the LC78624E performs C1
error checking and correction in the C1 block, determines the C1 flags, and writes data to the C1 flag register. Next,
the LC78624E performs C2 error checking and correction in the C2 block, determines the C2 flags, and writes data
to internal RAM.
C1 flag
No errors
1 error
2 errors
3 errors or more
Error correction and flag processing
No correction required · Flag reset
Correction · Flag reset
Correction · Flag set
Correction not possible · Flag set
C2 flag
No errors
1 error
2 errors
3 errors or more
Error correction and flag processing
No correction required · Flag reset
Correction · Flag reset
Depends on C1 flags*1
Depends on C1 flags*2
Note: 1. If the positions of the errors determined by the C2 check agree with the C1 flags, the correction is performed and the flags are cleared.
However, if the number of C1 flags is 7 or higher, C2 correction may fail. In this case correction is not performed and the C1 flags are taken as
the C2 flags without change. Error correction is not possible if one error position agrees and the other does not. Furthermore, if the number of
C1 flags is 5 or under, the C1 check result can be seen as unreliable. Accordingly, the flags will be set in this case. Cases where the number of
C1 flags is 6 or more are handled in the same way, and the C1 flags are taken as the C2 flags without change. When there is not even one
agreement between the error positions, error correction is, of course, impossible. Here, if the number of C1 flags was 2 or under, data that was
seen as correct after C1 correction is now seen as incorrect data. The flags are set in this case. In other cases, the C1 flags are taken as the
C2 flags without change.
2. When data is determined to have three or more errors and be uncorrectable, correction is, of course, impossible. Here, if the number of C1
flags was 2 or under, data that was seen as correct after C1 correction is now seen as incorrect data. The flags are set in this case. In other
cases the C1 flags are taken as the C2 flags without change
No. 5811-24/27