LC78624E Datasheet, PDF (20/27 Pages) Sanyo Semicon Device – Compact Disc Player DSP

LC78624E
16. Interpolation Circuit
Outputting incorrect audio data that could not be corrected by the error detection and correction circuit would result
in loud noises being output. To minimize this noise, the LC78624E replaces the incorrect data with linearly
interpolated data based on the correct data on either side of the incorrect data. If one set of C2 flags indicate errors,
the above replacement is performed, and if two or more sets of C2 flags indicate errors, the IC holds the previous
value. However, when correct data is output following two or more consecutive C2 flags indicating errors, the data
point between the correct data and the data output two points previously (the held value) is replaced with a value
computed by linearly interpolating those two values.
Data holding the
previous value
17. Audio Data Output; Pin 42: LRSY, Pin 43: CK2, Pin 44: ROMXA
A09918
The ROMXA pin provides the interpolated audio data, MSB first, synchronized with the edges of the LRSY signal
using the following timing.
18. Text Block
The text block decodes the song titles and other text data stored in the Subcode R through W channels of the compact
disc’s read-in area.
A data pack consists of 24 symbols (24 × 6 = 144 bits) or 18 bytes (18 × 8 = 144 bits). These 18 bytes consist of a 4-
byte ID field, 12 bytes of text data, and a 2-byte CRC. The 1-bit result of the CRC check (“H” for OK, “L” of NG)
for the pack plus the 16 bytes of ID and text data are available to the microcontroller. The chip indicates the
availability of this data with a “L” level pulse (min. 60 µs, max. 150 µs) from the DQSY pin. When the DQSY pin
goes to “L” level, the microcontroller reads this data by supplying 128 clock pulses to the SCLK pin. The time limit
for reading this data is 3.3 ms for normal playback and 1.5 ms for double-speed playback. The ID bits tell the
microcontroller how to interpret the text data that follows.
No. 5811-20/27