BBK PV420S, Service Manual

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CXD3068Q
§ 4-6. Servo Auto Sequence
This function performs a series of controls, including auto focus and track jumps. When the auto sequence
command is received from the CPU, auto focus, 1-track jump, 2N-track jump, fine search and M-track move
are executed automatically.
The servo block operates according to the built-in program during the auto sequence execution (when
XBUSY = low), so that commands from the CPU, that is $0, 1, 2 and 3 commands, are not accepted. ($4 to
E commands are accepted.)
In addition, when using the auto sequence, turn the A.SEQ of register 9 on.
When CLOK goes from low to high while XBUSY is low, XBUSY does not become high for a maximum of
100µs after that point. This is to prevent the transfer of erroneous data to the servo when XBUSY changes
from low to high by the monostable multivibrator, which is reset by CLOK being low (when XBUSY is low).
In addition, a MAX timer is built into this LSI as a countermeasure against abnormal operation due to
external disturbances, etc. When the auto sequence command is sent from the CPU, this command
assumes a $4XY format, in which X specifies the command and Y sets the MAX timer value and timer
range. If the executed auto sequence command does not terminate within the set timer value, the auto
sequence is interrupted (like $40). See [1] "$4X commands" concerning the timer value and range. Also, the
MAX timer is invalidated by inputting $4X0.
Although this command is explained in the format of $4X in the following command descriptions, the timer
value and timer range are actually sent together from the CPU.
(a) Auto focus ($47)
Focus search-up is performed, FOK and FZC are checked, and the focus servo is turned on.
If $47 is received from the CPU, the focus servo is turned on according to Fig. 4-6. The auto focus starts
with focus search-up, and note that the pickup should be lowered beforehand (focus search-down). In
addition, blind E of register 5 is used to eliminate FZC chattering. Concretely, the focus servo is turned on
at the falling edge of FZC after FZC has been continuously high for a longer time than E.
(b) Track jump
1, 10 and 2N-track jumps are performed respectively. Always use this when the focus, tracking, and sled
servos are on. Note that tracking gain-up and braking-on ($17) should be sent beforehand because they
are not involved in this sequence.
• 1-track jump
When $48 ($49 for REV) is received from the CPU, a FWD (REV) 1-track jump is performed in
accordance with Fig. 4-7. Set blind A and brake B with register 5.
• 10-track jump
When $4A ($4B for REV) is received from the CPU, a FWD (REV) 10-track jump is performed an
accordance with Fig. 4-8. The principal difference from the 1-track jump is to kick the sled. In addition, after
kicking the actuator, when 5 tracks have been counted through COUT, the brake is applied to the actuator.
Then, when the actuator speed is found to have slowed up enough (determined by the COUT cycle
becoming longer than the overflow C set with register 5), the tracking and sled servos are turned on.