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3.3.4
Fault
The
Fault line indicates to the host system that a condition
exists
on
the
disk
drive
that is going to cause improper
writing on the disk.
When this line is logically low (true),
Write
Data
is
inhibited and further writing on the disk is
pro-hibited
until the condition is corrected.
The condition
under
which
the
Fault line goes true is that D.C. voltages
are grossly out of tolerance.
3.3.5
Line Ready
In
conjunction
with
the Seek Complete line, the Line Ready
line
indicates
to
the
host system that the disk drive can
read, write or seek, and that all I/O signals are valid.
The
Line
Ready
line
goes logically low (true) approximately 15
seconds
after
power
on. The Line Ready line goes logically
high
(false) if the drive is not selected or if the speed of
the
motor
is too slow. When this line is false, all writing
and seeking is inhibited.
3.3 .. 6
Index
An
index
pulse is provided
once every revolution (16.67 ms
nominal)
to
indicate
the
beginning of a track to the con-
troller.
The
transition
from
logically
high (false) to
logically
low
(true)
is
the
only
valid transition.
The
leading
edge
of
the
pulse must be used to ensure accurate
timing.
3.4
DATA TRANSFER LINES
The Data Transfer lines transfer information between the host
system
and the disk drive when the drive is selected.
These
lines
are
differential
in nature.
They may be multiplexed
when us ing Drive Se lect
.0
The
MFM
Write Data pair of lines and the MPM Read Data pair
of
lines
are provided for the transfer of data.
Figure
9
contains
q
typical
driver/receiver
circuit combination used
for data transfer signals.
3.4.1
The
MFM
provide
on
the
MFM Write Data
Write
Data
lines
are
the differential pair that
the data to be stored on the track.
A flux reversal
track
to be written is caused When the plus
(+)
MFM
3-6
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