Servo Control; Servo Control Circuit; Block Diagram Of Servo Control Circuit (Maj3364) - Fujitsu MAH3182MC Maintenance Manual

8.7

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 8.5).
8.7.1

Servo control circuit

Figure 8.4 is the block diagram of the servo control circuit. The following explains each function
of the servo control circuit.
Servo system block diagram
Data surface
signal
Data
Servo
head demodulator
bus8
HDC
Figure 8.4
(1) Processor-ASIC (Processor-application specific IC)
A DSP controls the spindle motor and the voice coil motor. The SCSI sends an instruction to the
DSP through the SCSI control MCU via drive interface. The Processor is a 1-chip ASIC, and also
contains an analog-to-digital converter, a digital-to-analog converter, RAM, and other logic
circuits.
(2) Servo demodulator
As explained in 8.7.2, servo signals consist of a training segment, a Servo Mark segment, a
Position segment and a Gray Code segment, and 84 frames for MAJ series and 108 frames for
MAH series are arranged around the circumference. In the servo demodulator, the Gray Code and
Position signals from the servo signal are demodulated and used to control head positioning.
8 - 10
Processor
DSP
Core
bus16
Drive
bus16 bus16
I/F LSI
MCU
FMC16

Block diagram of servo control circuit (MAJ3364)

C141-E103-01EN
DSP controlled actuator servo system
MCU controlled spindle servo system
Control signal
(PWM)
SPM/VCM
bus16
combo
Control
signal
FET
VCM
ARRY
FET × 3
Spindle
motor