The control output signais are gated to the interface when selected. They are:
DRIVE SELECTED, INDEX, TRACK
0,
READY, SEEK COMPLETE and
WRITE
FAULT.
5.1
DRIVE SELECTED
5.0
CONTROL
OUTPUT
SIGNALS
DRIVE SELECTED
is
a status signal transmitted over 12, which informs the
host system
of
the selection status
of
the drive. The signal
is
driven by a TTL
open collector, as illustrated in
Figure
10.
The signal goes low (true)
on
the in-
terface only when the device is correctly configured (see
Sections 3.1-3.5) and
the DRIVE SELECT line
is
activated by the host system.
5.2
INDEX
This signal
is
provided by the drive once each revolution to indicate the begin-
ning
of
a track. The nominal period
is
16.67 msec., with a typical pulse width
of
1.5 msec. Normally this signal
is
at
a nigh
level
and the transition to low indi-
cates INDEX. Only the transition from high to
low,
or the leading edge,
is
valide
5.3
TRACK
(()
This signal
is
low (true) only when the Read/Write heads are positioned at
Cylinder Zero.
Track
0
is
the only cylinder
that
provides interface recognition. The drive
is
designed to recalibrate to Track 0 during power-on and Auto-Truncation oper-
ations.
Track
0 may also be accessed via conventional Buffered-Seek
and
Slow-Step
modes. After Track
0 is true, no actions may be taken
by
the controller until
SEEK COMPLETE
is
also true.
5.4
READY
This signal, when true together with SEEK COMPLETE, indicates that the drive
is
ready to Read, Write
or
Step and that aIl control input signais are
valide
When
this line is high, aIl reading, writing and stepping are inhibited. The typical time
after power-on for READY
to
be true
is
24 seconds.
READY remains false during the power-up sequence until:
1.
The recaIibration to Track
10
is complete
2.
Spindle speed
is
stable within ±
1070
of
nominal
3. Drive initialization routines are complete
4.
DC
voltages are within tolerance.
18
ST212
PRODUCT
MANUAL/Rev.
B
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