The following actions will clear (or prevent)
an
illegal address indication.
(1)
An address within the legal range is present with the strobe.
(2)
A RESTORE INITIAL CYLINDER operation is commanded.
(3)
The disk drive becomes not-ready as the result
of
an
operator-initiated Unload or
Emergency Unload operation.
3.17.9
FILE PROTECTED
The level on
this
line indicates the selected platter is protected from a Write operation.
When the
FILE PROTECTED line is low,
it
indicates that the drive
will
not
perform a Write
or Erase operation regardless
of
a command on the WRITE ENABLE or ERASE ENABLE
lines; when the FILE PROTECTED line is high,
it
indicates that the selected platter is not
protected and data may be written.
Depending upon the configuration of the disk drive, write protection may be provided
for
either or both platters.
Changes
of
state on
this
line,
as
applicable,
will
occur within 1.0
fJ.sec
of
a platter select
change (assuming the unit is selected).
It is recommended that the controller test the state of the line prior
to
attempting a Write
operation.
3.17.10 MALFUNCTION DETECTED
This is a plse which, when low, indicates detection
of
one
of
the
following
malfunctions.
(1)
Loss
of
ac or
dc
power.
(2)
Disk speed does not remain within tolerance.
(3)
Positioner error is detected.
(4)
Write circuit faults that could affect stored data.
Any
of
the above items listed necessitate unloading the heads and the drive will
commence
an
emergency unload sequence coinCident with the trailing edge
of
the
malfunction pulse; duration
of
the pulse is between 0.2
fJ.sec
and 2.0
IJ.sec.
Any disk drive on the
I/O
bus can pulse
this
line regardless
of
whether
or
not it is selected.
The line
will not be pulsed
if
the malfunction is detected before the drive achieves a Ready
condition. The drive
will
become not-ready within 5.0
IJ.sec
after the leading edge
of
the
pulse
on
the MALFUNCTION DETECTED line. Software diagnostics can determine which
drive has detected a malfunction by selecting one drive at a time, determining
its
ready
status, and comparing the results with the previous status.
As all disk drives on the
1/0
bus could pulse the MALFUNCTION DETECTED line
asynchronously and independently, the time between pulses in a group may become
arbitrarily
small.
I
n the case
of
power fai lures, etc., the pulses may overlap or occur simultaneously.
NOTE
It
is recommended that the leading edge
of
a malfunction
pulse be used to initiate diagnostic action and that once
the condition has been flagged,
additional
pulses can be
disregarded
until
after the flag
is
cleared.
The
flag need
not
be cleared before diagnostic action is commenced.
3-22
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