LC78681E Datasheet, PDF (11/23 Pages) Sanyo Semicon Device – Digital Signal Processor for Compact Disc Players

LC78681E
Note: * For constant linear velocity servo control commands, the TOFF pin is low only in the CLV mode; otherwise it is high. Control of the TOFF pin by
command is effective only in the CLV mode.
1. CLV Mode
• In the CLV (constant linear velocity) mode, the LC78681E detects disc speed from the HF signal and switches the
internal DSP mode to perform various types of control for maintaining the correct linear velocity. The pulse-width
modulation cycle is 7.35 kHz, and the 1/64 duty cycle is 1.114 s. V/P outputs high during rough servo and low
during phase control.
Internal mode
Rough servo (velocity too low)
Rough servo (velocity too high)
Phase control (PLCK locked)
CLV⁺
High
Low
PWM
CLV^–
Low
High
PWM
V/P
High
High
Low
2. CLV Control Gain Switching
MSB
LSB
10101000
10101001
Command
DISC 8 set
DISC 12 set
RES = low
CLV control gain during rough switching for 8-cm discs can be set at 8.5 dB lower than for 12-cm discs.
3. Internal Brake Mode
MSB
LSB
11000101
11000100
10100011
Command
Internal brake on
Internal brake off
Internal brake control
RES = low
• The internal brake mode is enabled when an Internal Brake On command (C5H) is input. Executing a Brake
command (06H) in this mode allows the deceleration of the disk to be monitored at the WRQ pin.
• In this mode, the EFM signal density per frame can be counted to determine the status of disc deceleration. When
there are fewer than four EFM signals, CLV^– falls to low, and the WRQ pin simultaneously goes high to indicate that
brakes is completed. The microprocessor issues a Stop command when it senses that the WRQ pin is high, thereby
completing the stopping of the disc.
No. 4521-11/23