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nsTPo,NT7-nl....------1L
1.-4 MIWaCONDS AV!IIAGI
~-------200 MILUaCONDS--------I-l
FIGURE 4-5
SOfT SECTORED INIJEX PIJLSE
Write Protect Switch
The
Write
Protect
signal
is
derived
from
a
mechanical
switch
integrated
into
the drive,
the switch is deactivated, causing a high
signal
on
,Jll,
Pin 5.
Then,
it is buffered and inverted to disable
the
Write
Enable
signal.
It
is
also
gated
with
drive select,
producing an output signal on the interface.
Track 0 Sensor
The
Track
0
sensor
signal is derived from an infrared L. E. D. and
phototransistor
internal
to
the
drive.
As the head carriage moves
back toward Track 0,
the sensor is activated between Tracks 0 and
2.
This
low
active
signal
comes
in via
J~,
Pin
4.
It is inverted by
IC
U~.
The combination of the Track 0 sensor being activated and the
proper
stepper
motor phase (Phase 0) produces a
low output at IC UH,
Pin 6 (Test Point 10).
This signal is buffered through IC U17,
Pins
~
and H, to be gated with drive select at IC UlH, Pins
~
and 10,
to give
a
Track
0
output
to Pin 26 of the interface.
After IC U17, Pin R,
this
signal is gated with direction (IC U7,
Pin 12) at Ie U6, Pins 12
and 13.
IC U6, Pin II, when true low inhibits stepping to Track 0 mInus 1.
4-5
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