User's Manual

4.7 Servo Control
4.7.3 Servo frame format
As the servo information, the IDD uses the phase signal servo generated from the
gray code and servo EVEN and ODD. This servo information is used for
positioning operation of radius direction and position detection of circumstance
direction.
Basically, the servo frame consists of 5 blocks; write/read recovery, servo mark,
gray code, Burst EVEN1, Burst ODD, Burst EVEN2, and PAD. Figure 4.8 shows
the servo frame format.
Write/read
recovery
Servo
mark
Gray code Burst
EVEN1
Burst
ODD
Burst
EVEN2
Post
code
(particular
models
only)
PAD
Figure 4.8 Servo frame format
(1) Write/read recovery
This area is used to absorb the write/read transient and to stabilize the AGC.
(2) Servo mark
This area generates a timing for demodulating the gray code and position-
demodulating the burst signal by detecting the servo mark.
(3) Gray code (including sector address bits)
This area is used as cylinder address. The data in this area is converted into the
binary data by the gray code demodulation circuit.
(4) Burst Even1, Burst Odd, Burst Even2
These areas are used as position signals between tracks and the IDD control so that
target phase signal is generated from Burst Even and Burst Odd.
(5) Post code (particular models only)
This area is used for the precise correction of the servo information which is
recorded on the media.
(6) PAD
This area is used as a gap between servo and data.
C141-E259 4-17