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5.7 Servo Control
The servomechanism is controlled using a digital servo technique by the firmware in the digital
signal processor (DSP).
DPS carries out VCM control. Control of the voice coil motor consists of track-following
operation control and seek operation control. Track-following operation is controlled to center
the data-head-mounted actuator over the target cylinder for read/write operation. The seek
operation moves the actuator to a different target cylinder at high speed. For stable operation, a
variety of calibration is done (see Section 5.5).
5.7.1 Servo control circuit
Figure 5.5 is the block diagram of the servo control circuit. The following explains each function
of the servo control circuit.
Data surface
signal
Data
head
Drive
I/F LSI
DSP
Core
bus8 bus16
bus16
SPM/VCM
combo
Servo
demodulator
Control signal
MCU
FMC16
HDC
FET
×
2
FET
×
3
VCM
Spindle
mo to r
Servo system block diagram
bus8
bus8
Control signal
(PWM)
Processor
Notes: DSP controlled actuator servo system
MCU controlled spindle servo system
Figure 5.5 Block diagram of servo control circuit
(1) Processor-application specific IC (Processor-ASIC)
A DSP controls the spindle motor and the voice coil motor. The SCSI sends an instruction to the
DSP through the SCSI control MCU and native interface. The DSP is a 1-chip Processor-ASIC,
and also contains an analog-to-digital converter, a digital-to-analog converter, RAM, and other
logic circuits.