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4.4
READ/WRITE HEAD PUSITIONER
The components of the drive required to position the read/write
head(s) at the desired track are:
1.
Step and direction circuits
2.
Stepper motor control circuits
3.
Stepper motor
Step and Direction
The
Step
and
Direction signals are derived from the host controller
via interface connector J8, Pin 20, and J8, Pin 18, respectively.
The
direction
line
is
buffered
and
inverted
on the control and
read/write
circuit
board and sent to the motor control circuit board
via JIO, Pin 1.
On the motor control circuit board,
it is used as the
D input of IC U6, Pin 12, the direction flip-flop;
The
step
pulses
are
buffered by IC U17, Pins 1 and 2, and gated
with
Drive Select at IC U8, Pins" and 10.
IC U8, Pin 8,
is inverted
by IC U7, Pins 1 and 2.
Test Point 11 can
be
used to monitor the step
input,
which
is
output
at JIO, Pin 3, to the motor control circuit
board.
On
the motor control circuit board, the step pulses are used to clock
the
direction
flip
flop
IC U6 at Pin 11 and the step one shot flip
flop (time is two microseconds) at IC U8, Pin 10.
Generation
of
controlling
signals
for
accomplished
via
IC
U7.
The direction
down
counting
of
the
step pulses (two
U7.
correct
stepping phases
flip flop controls the up
pulses per track) used by
is
or
IC
IC
U8,
Pin
12, when clocked by a step pulse will clock IC U7 at Pin
14,
thus
Pin
3
of IC U7 wi
11
trigger a 10-mi 11 isecond one shot at IC
U8, Pin
2, which retriggers the two microsecond step flip flop IC U8,
Pin
9.
IC U7 is clocked again to complete a single phase rotation of
the stepper motor through logic driver IC's Ul and U2.
NOTES
THE TIMES IN THE ABOVE DESCRIPTIUN ARE fUR THE
20-MILLISECOND STEPPER MOTOR.
FOR ADDITIONAL
INFORMATION, SEE TABLE 1, SHEET 1 OF
3,
MUTOR
CONTROL SCHEMATICS FOR COMPONENT VALUES AND
CHANGES fOR SIX-MILLISECOND STEPPER MUTORS.
PHASE 0 Of THE STEPPER MOTOR IS ACTIVE ON ALL
EVEN TRACKS: 0, 2, 4, 6.
4-7
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