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Functional Description
7936 and 7937
5-29. Servo Control Bus. The signals which the
servo controller exchanges with the microprocessor
in controller PCA-A6 over the Servo Control Bus
are detailed below:
SOO-S07
SBF-L
SOAV-L
SPR-L
SRO-L
SWR-L
Servo Data Bus
Servo Buffer Full
Servo Data Available
Servo Processor Reset
Servo Read
Servo Write
Servo Data Bus (SOO-S07) is an 8-bit bidirectional
bus which interconnects the microprocessor in
controller PCA-A.6 with the servo controller.
Servo Buffer Full (SBF-L) indicates that the mic-
roprocessor in PCA-A6 cannot accept any more
status bytes from the servo controller.
Servo Data Available (SOAV-L) indicates that the
microprocessor has a command byte ready for the
servo controller.
Servo Processor Reset (SPR-L) allows the micro-
processor to reset the servo controller.
Servo Read (SRO-L) permits controller PCA-A6 to
drive
the
bus
with
a
byte
of
command
information.
Servo Write (SWR-L) indicates that the servo con-
troller is driving the bus with a byte of servo
inf orma tion.
5-30. Servo Controller Input and Output Signals.
The servo controller exchanges the following sig-
nals with the drive electronics:
AGCF-L
AMPFLT-L
0100,0101
GBO-H
OFTRK-H
SPOSNS-L
SRTF-H
SSGT-L
TRKCR-H
5-16
INPUTS
AGC Fault
Amplifier Fault
Drive ID
Guard Band Detect
Offtrack Latched
Speed Sense
Servo Timing Fault
Sampled Servo Gate
Track Crossing
Signal SPOSNS-L is from the spindle drive system
(see figure
iD )
and the remainder of the signals
are from components of the servo system (see
figures
II
and
II ).
ACQUIRE-H
AMPEN-H
CLER-L
CLSER-L
FSEN-L
GOBEN-H
LCK-L
LSB-H
NACC-L
PACC-L
QUAO-H
SCAP-L
SOSEN-H
SSSL-H
OUTPUTS
Acquire
Amplifier Enable
Clear Error
Clear Servo Error
Fine Servo Enable
Guard Band Enable
Lock
Least Significant Bit
Negative Acceleration
Positive Acceleration
Quadrature
Start Capacitor
Start of Sector Enable
Sampled Servo Select
The majority of the outputs from the servo con-
troller are connected to the dedicated servo circuit,
sampled servo circuit, and servo power amplifier.
Start Capacitor (SCAP-L) is output to the spindle
drive system. See figure
iii .
The functions of the servo controller input and
output signals are described in table 5-1 and related
circuit descriptions.
5-31. 2-BIT ADC. The servo controller monitors
head shift (dedicated track/sampled track offset)
and adjusts for it. The measurement of head shift
is done while track following on the sampled ser-
vo, after a seek command has been received, but
before the seek is begun by the servo controller.
The 2-bit analog-to-digital converter (ADC) is con-
tinuously monitoring Dedicated Servo Position
Error (OPOS) to a sign and a single bit of
amplitude.
From
a
OPOS/in-phase
versus
OPOS/quad dedicated servo code measurement,
the servo controller can determine how much head
shift the present data head has (relative to the ser-
vo head), and can adjust the subsequent seek
accordingly.
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