830D
To
prevent removal
of
a cartridge during unsafe conditions, the cartridge lock arm will
be
locked whenever the drive is not in a Safe condition.
In
addition to the
electro~mechanical
interlock protection, additional interlocking is
provided via certain logic within the disk drive.
If the operator should actuate the
RUN
I
STOP
switchl
indicator, or
if
the interface should command a Stop sequence as a result of
a change
of
state on the START I
STOP
DISK
DRIVE
line during the time that a Write
andlor
Erase operation is in progress, the heads will not
be
unloaded immediately from
the storage surfaces
even
though the disk drive prepares to execute a Stop sequence.
Only when the controller has completed the current Write
and/or
Erase operation will the
heads
be
unloaded from the storage surface. This prevents the loss
of
data in the event
that the operator attempts to stop the disk drive during the time that a write data transfer is
in progress.
An
additional interlock prevents changing the Write Protect status during a Write
andlor
Erase operation. If either a Write
and/or
Erase operation is in progress, the status
of
the
write protection cannot
be
changed electrically regardless of the pOSitions of the
WRITE
PROTECT
switches.
Only after completion of the current Write and I or
Erase
operation will the write protection
status change to agree with the particular switch setting.
This is primarily applicable to top load models, although the same logic is present
In
all
machines.
The
purpose
of
this arrangement is to prevent loss of data in the event
an
operator should change the condition of the WRITE
PROTECT
switches during the time
the controller is in the process
of
a write data transfer.
3.12 SAFE CONDITION
The
Safe condition for both front and top load models is indicated by Illumination of the
SAFE indicator
and
is defined by:
(1)
Power correctly applied.
(2)
Disk not rotating.
(3)
Heads retracted.
(4)
Emergency
or
fault conditions not being detected
by
the logiC.
(5)
Disk drive not executing a brake cycle or a stop sequence.
It should
be
noted that although the disk drive is in a Safe condition,
it
is not necessarily
enabled
to
respond
to
start commands.
The
conditions which inhibit starting the disk drive
are:
(1)
The cartridge Is not properly Inserted.
(2)
Power
is
not applied.
(3)
An
internal emergency or fault condition exists
and
is being detected.
(4)
The ACTIVATE EMERGENCY UNLOAD line is being asserted.
3-10
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