3.13 EMERGENCY AND FAULT DETECTION
When power
to
a disk drive Is lost when the disk Is spinning,
it
is impossible
for
the disk
drive
to
maintain disk speed at a value which assures that the heads
will
continue
to
fly
above the surface of the disk.
In order
to
protect the data and the cartridge,
as
well
as
the
disk
drive, It Is necessary to
remove the heads from the surface
of
the
disk
as fast as possible when a power fault Is
detected. The process
of
removing the heads from over the
disk
in
an emergency situation
is referred
to
as Emergency Unload. Additionally, there are other conditions which are
undesirable, either from the standpoint
of
potential hazard
to
data
or
to
the
disk
drive.
It is also important
to
be able to communicate emergency conditions
to
the disk drive via
the
ACTIVATE EMERGENCY UNLOAD interface line and cause the
disk
drive
to
enter
an
Emergency Unload mode. This is appropriate in situations when a fault or the failure of
power to the computer
and/or
controller could result
In
a situation where the controller
can no longer maintain control
of
the interface lines. All of these conditions are sensed by
the disk drive logic and one
or
more
of
these conditions may cause the
disk
drive to
perform an emergency unload.
Notwithstanding conditions communicated via the
ACTIVATE EMERGENCY UNLOAD
Interface line, the conditions which can cause
an
emergency unload are summarized as
follows.
(1)
Loss of ac
or
de power.
(2)
Disk speed does not remain within tolerance or is at
an
incorrect speed at the time
it
is tested.
(3) Positioner error
Is
detected.
(4) Write
circuit
faults that could affect the stored data are detected.
3.14 MANUAL
CONTROLS
The operational controls and indicators are located on the front panel
of
the
disk
drive;
additionally, one
or
two
rocker-type switches may be located Inside the drive which
provide protection from inadvertent write operations. The following paragraphs describe
the functions
of
these controls.
3.14.1
ON/OFF
The
ON/OFF
power
control/s
a rocker-type
swltchlindicator
which provides the operator
a means
of
energizing and de-energizing the power
to
the drive. The indicator
is
illuminated when power is ON and the internal
+5v
power Is operational.
3.14.2 RUN/STOP
The RUN/STOP control
Is a momentary action
switchllndicator
which provides a means
for selecting the operational status
of
the drive. The alternate action arrangement is
provided by the
disk
drive logic. The control will
be
illuminated when actuated and the
drive has been properly conditioned to
allow the disk to
be
brought to operating speed.
When the
illuminated
switchlindlcator
is depressed again, a Stop sequence
will
be
entered and the disk
will
decelerate to a stop. The cartridge may be unloaded at
this
time.
If
a cartridge has been incorrectly inserted
or
an emergency condition exists, the operation
of the RUN/STOP
control
is
inhibited. Under
this
condition, the control
will
not
become
illuminated and the Run status
will
not be achieved.
~11
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