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4) Gray code area
The gray code is an encoded area which includes the head number, servo sector number and
cylinder information as gray code. Head position is recognized based on the cylinder
information embedded as a gray code pattern.
5) Position area
Information for recognizing head position is recorded in the position area. Head position in
cylinder unit is recognized by using the cylinder information in the gray code area, and head
position under one cylinder (resolution) is recognized by using the information in the position
area.
IGBDS Servo zone
Outer side of disk
Center of disk
OGB
Figure 8.5 Position of servo track
8.7.3 Servo frame format
Gap
Gray code/Position
Gap
Servo
mark
W/R recovery
Figure 8.6 Servo frame
8.7.4 Spindle motor control
The SCSI control MDU controls the senseless 3-phase spindle motor. It carries out start / normal
rotation control and spindle synch control in accordance with commands from the SCSI unit.
(1) Activation
The SCSI control MPU carries out control of the spindle motor from the stopped condition to
normal rotation by the following sequence.
1) DSP intermittently supplies current between specific phases (e.g., phases U and V) to force a
fixed motor rotation position. This operation is called alignment.
Data zone