Output Control Signals - Tandy 2000 Service Manual

DIRECTION IN
This signal defines the direction
of
motion
of
the
read/write head when the
Step
line is pulsed. An
open
circuit or logical
false defines the direction
as
"out". If
a pulse
is
applied
to
the
Step
line,
the
read/write
heads
move away
from the center
of
the
disk.
If
this line
is
true, the direction is defined
as
"in",
and the
read/write
heads
move in toward the
center
of
the disk.
Seek Complete
must be true
prior
to
changing
directions and
the
application
of
additional
step
prulses.
REDUCED
WRITE CURRENT
The
Reduced
Write
Current
input line
is
ter-
minat€d, but
is
not
used
in the TM500
series
drives.
The
microprocessor automatically switches write
current.
DRIVE SELECT
O
THROUGH DRIVE SELECT
3
These
control
signals
enable the selected drive's in-
put
receivers
and output drivers. When
logically
false, the output
drivers are open circuits and the
input
receivers
do not
acknowledge
signals
presented
to
them.
Selecting
the
appropriate
jumper block
at
W9
through W
12
determines which select line activates
the drive.
NOTE
Only one drive may be selected
at
a time.
OUTPUT CONTROL SIGNALS
The output control
signals are
driven with an open
collector output stage capable
of
sinking
a
mELx-
imum
of
n
milliamperes
in
a true
state,
with
a
mzurimum voltage
of
0.4 volt
measured
at
the
driver. When the line driver
is
in the
false
state, the
driver transistor is
off,
and the collector
cutoff
is
a
mrurimum
of
250 microamperes.
All
Jl
output lines are enabled
by
the
respective
Drive
Select lines.
SEEK COMPLETE
The Seek Complete signal goes
true
when
the
read/write
heads
have settled
on the final track
at
the end
of
a seek.
Reading
or writing should not
be
attempted when
Seek
Complete is
false.
Seek
Complete
goes false:
l.
When a recalibration
sequence
is initiated
.
by the microprocessor at power on
because
the read/write
heads
are
not over Track
0.
2.
500
nanoseconds, maximum, after the
trail-
ing
edge
of
a step pulse
or
a
series
of
step
pulses.
3.
When power
is
momentarily
lost,
Seek
Complete
is false when power
is
restored
and
remains
false
until an
automatic
recalibration is comPleted.
TRACK
O
The Track 0 signal indicates a
true
state
only when
the drive's read/write heads are positioned at Track
0, the outermost data track.
FAULT
The Fault signal is
used
to indicate a condition
ex-
ists
in the drive that could
cause
improper writing
on the disk. When this line
is
true, further writing
is
inhibited,
&s
are other drive functions,
until
the
condition is
corrected.
This condition
is caused
by either
the
+
12
volt
or
+
5
volt
supply dropping below the specified limits,
and on power up until
a successful
recalibration
se-
quence is completed.
INDEX
The Index signal is provided once
each
revolution,
16.7
milliseconds nominal,
to indicate the beginn-
ing
of
the
track. Normally, this
signal is false and
makes
the transition
to true to indicate Index. Only
the transition
from
logical false
to
logical true
is
valid.
3-r2