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LOWER SURFACE OF
BOTTOM DISK
I
I
I
I
I
rot~
rot.]
rotc"
rot,
rot.
I
FIGURE 1-18
SERVO WEDGES
1 DF
5~
SERVO
WEDGES ON DISK
..-... -
DISK 10
~
.....
-~-
TRACK
Ii.
. - - - - DISK 00
The servo read and conversion circuits detect the servo bursts and convert this analog information into digital
values that are used by the microprocessor to position the heads on the track center. Figure 1-19 shows a functional
block diagram of , the servo circuits. The actual circuitry is found in Figure 2-6.
Consult the block diagram to reference the following summary of the servo circuitry. The servo head reads ser-
vo bursts and sends the signal through an amplifier on the encoder board. Next, a filter attenuates the high frequen-
cy noise, which then passes through a second stage amplifier on the main board. The filtered and amplified signal is
peak detected with timing controlled by the microprocessor. Finally, an AID converter transforms the AB peak
detected bursts from an analog signal to an 8 line digital signal that goes to the microprocessor.
The microprocessor reads the A burst and compares it to the last B burst using the formula:
32 (A-B), if on an odd track
A+B
32 (B-A), if on an even track
A+B
The microprocessor outputs digital values to the D I A converter, which converts them to an analog voltage.
Finally, the actuator driver converts the analog voltage signal to a current to move the actuator.
PI
~
DISK
ANALOG
SERVO
SERVO
SECOND
TPf
PEAK
SWITCH
BURSTS
SERVO
READ
DETEC
STAGE
HEAD
AHP
&
I
TOR
F I L TER
A.'IP
1
ENABLE
FROM MiCROPROCESSOR'!
AID
8
M I CRO-
CONV[H
....
TER
,
PROCESSOR
FIGURE 1-19
SERVO CIRCUITRY BLOCK DIAGRAM
REV A (01/84)
1-20
B
TO
DIA
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