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Input Control Lines
Drive select Lines
The
Drive Select lines provide a means of selecting and deselecting a
drive.
These four lines select one of the four drives attached to the
controller.
When
the
signal logic level is true (low),
the drive electronics are
activated,
and
the
drive is conditioned to respond to Step or Read/
Write
commands.
A Drive Select line must remain stable in the true
(low)
state
until
a
Step or Read/write command is completed.
When
the
si<Jnal
line logic level is false (hiCJh),
the input control lines
and output status lines are disabled.
The drive address is determined by a select shunt on the logic circuit
board.
Drive
Select
lines
0
through
3 provide a means of daisy
chaining
a
maximum of four drives to a controller.
Only one can
be
true
(low)
at
a
time.
An
undefined operation results if two or
more
drives
are
assigned
the
same address or if two or more Drive
Select lines are in the true (low) state simultaneously.
Motor On
When
this
signal
nominal
speed
of
one
second.
When
drive
decelerates
Drive Select.
is
true (low), the drive motor accelerates to its
300 RPM, and stabilizes at this speed in less than
the signal line logic level goes false (high),
the
to
a
stop.
This
signal is not gated with
Direction Select and Step Lines (Two Lines)
When
the
drive
is selected, a true (low) pulse on the Step line,
with
a
time duration greater
than
200
nanoseconds,
initiates
the
access
motion.
The direction
of motion is determined by the logic
state
of
the
Direction Select
line
when
a
step pulse is issued.
The
motion is toward the center
of
the disk if the Direction Select
line is in the true (low) state.
The direction of motion is away from
the
center
of
the disk if the Direction Select line is in the false
(high) state.
To
ensu re
stable
at
pulse, and
proper
positioning,
least 100 nanoseconds
remain true (low) 100
the
Direction Select line should be
prior to issuing a corresponding step
nanoseconds after it.
The access motion is initiated on the trailing edge of the step pulse.
The
time
period
between
consecutive
trailing edges of step pulses
should be at least 20 milliseconds.
3-4
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