10. Text circuit

The text function decodes and outputs the song titles and other text data written to the subcode R through W channels

in the compact disc read entry area.

A single pack, which is the subcode R through W data for 24 symbols (18 bytes = 144 (24

× 6 = 18 × 8) bits),

consists of 4 bytes of ID data, 12 bytes of text data, and 2 bytes of CRC data. The data that can be read out from the

LC78628E consists of a result flag for the CRC check (1 bit) and the 16 bytes of the ID and text data. When the IC is

in a state where the data can be read out, it outputs a low-level pulse (minimum: 60 µs, maximum: 150 µs) from the

DQSY pin and outputs, from the SRDT pin, the CRC check result flag (OK: high, NG: low) for the one pack of data

that can be read out. After the control microprocessor detects the low level on the DQSY pin, it can read out the data

serially from the SRDT by applying 128 transfer clock pulses to the SCLK pin. The application must complete the

readout of one pack of data within 3.3 ms in normal-speed playback mode, and within 1.5 ms in 2

× -speed playback

mode. Since the type and other information concerning the following text data is encoded in the ID data, the control

microprocessor must interpret the text data according to the ID data.

No. 6329-21/40

LC78628E

Data for one pack

1 packet = 4 packs

SBSY

DQSY

SCLK

SRDT

DQSY

SCLK

SRDT

CRC D0 D1 D2 D3 D4 D5 D6

D127

D0 D1 D2 D3 D4 D5

D126

•••••••••

•••••••••

•••••••••

•••••••••

CRC

•••••••••

A12819

: Correct data

: Flagged data

: Linearly interpolated data

: Data converging

to the mute level

A12820

Code

Command

RES = low

$01

MUTE

0 dB

$02

MUTE

–12 dB

$03

MUTE

–

∞ dB

q

q

An attenuation of 12 dB (MUTE –12 dB) or full muting (MUTE –

∞ dB) can be applied by issuing the appropriate command from the table. Since zero cross

muting is used, there is minimal noise associated with this function. Zero cross is defined for this function as the top seven bits being all ones or all zeros.

Caution: Note that it may become impossible to detect HDCD discs if either the $02 or $03 instruction is executed.

11. Muting control circuit

12. Interpolation circuit

The output of incorrect audio data that could not be corrected by the error detection and correction circuit would

result in loud noise in the output. To minimize this noise, the LC78628E replaces the incorrect data with linearly

interpolated data based on the correct data on either side of the incorrect data. More precisely, the LC78628E uses

this technique if C2 flags occurred up to three times in a row. If C2 flags occurred four or more times in a row, the

LC78628E converges the output level to the muting level. However, when correct data is finally output following

four or more C2 flag occurrences, the LC78628E replaces the 3 data items between the data actually output at the

fourth preceding item and the correct data with data linearly interpolated between those two values.