6300
The normal front-loading cartridge has sector slots for the purpose of sectoring and a
Single index slot in the sector ring for purposes of mechanical sectoring. Special
front-load cartridges may
be
designed with only
an
index slot.
Referring to Figure 4-12, the Upper Sectorllndex
Sensor is a photoelectric type of sensor
for front load models
and
a magnetic transducer for top load models.
The
Lower
Phase/Index Sensor is a magnetic transducer on all 03000 models. This magnetic
transducer senses the notches in the
Phase Lock Ring mounted
on
the spindle. The Phase
Lock Ring is used for electronic sectoring
and
for speed control of the spindle. The slots
or notches in the removable cartridge are sensed
by
the appropriate sensor type and the
signal is fed to the Upper
Sensor Detector which converts the analog Signal from the
sensor to a digital pulse train.
The
pulse train, however, contains either all the pulses for
the sector slots, or notches, and
in
addition a pulse for the index slot or notch,
or
in the
case
of
index-only cartridges
just
a single pulse
for
the index notch.
In
the event that pulses for the sector slots
or
notches and the index slot or notch is
present, these
will be separated by the Upper Time Demultiplexer. The pulse representing
the index
will
be
output
on
one line from the Upper Time Demultiplexer and the sector
pulses
will
be
output
on
another line. Therefore,
it
can
be
said that the Upper Time
Demultiplexer functions to separate the index pulse from the
~ector
pulse. It
is
important
to note that these pulses
are
pulses representative of sensing of the slot and are not the
Signals fed
to
the interface. The specific gate time required
by
the Upper Time
Demultiplexer is programmed
by
a Programming Array, and the basic time reference used
is obtained from a clock
Signal generated in the Clock Countdown portion of the
Start / Stop Control logic.
In
the case when
an
index-only cartridge is being used, a single pulse per revolution is
applied to the input
of
the Upper Time Demultiplexer. The output
of
the Upper Time
Demultiplexer
will
be
a single pulse
on
the same line that
was
used for outputting the
demultiplexed sector information in the previously mentioned case.
The Lower
Sensor Detector is a circuit similar to the Upper Sensor Detector except that
it
has a variable threshold. The circuit converts the analog signal from the Phase Lock Ring
magnetic transducer to a digital signal which is applied to the Lower Time Demultiplexer.
The
purpose
of
the Threshold Control for the Lower Sensor Detector is to provide a means
for changing the sensitivity of the Lower
Sensor Detector. When executing a stop
sequence, or when the disk drive is in the
Safe condition,
it
Is desirable to
be
able to detect
any rotation
of
the spindle; this is accomplished by causing the Lower Sensor Detector to
operate
in
a high sensitivity mode via the Threshold Control logic. This high sensitivity
threshold is enabled when Drive Motor Enable (LDMEG) is not asserted. When Drive Motor
Enable is asserted, the threshold is changed to a threshold similar to that used in the
Upper
Sensor Detector. Drive Motor Enable is asserted whenever the disk drive is in the
Run
condition.
The Lower Time Demultiplexer functions
in
a manner similar to the Upper Time
Demultiplexer except that the
Phase Lock Ring always has a single index notch per
revolution which is interposed between the phase lock notches. The Lower Time
Demultiplexer will output the
Index pulse
on
one line and all the other phase lock notch
pulses
on
the other line. Thus, the Lower Time Demultiplexer separates the pulses
obtained from the phase-lock notches from the single index notch. The value of the gate
time required
by
the Lower Time Demultiplexer is programmed by the Programming Array.
The
time reference for the Lower Time Demultiplexer is obtained from a clock signal
generated by the Clock Countdown Circuitry
in
the Start/ Stop Control logic.
4-28
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