Specifications
2.2.1
DrIve
Select
1-4
..
DRIVE
SELECT,
when logically true, connects the
drive
to the
control
Una.
Only
one
DRIVE
SELECT
line
may
be
active
at
a time.
Jumper options
051-4
are used to choose
which
DRIVE
SELECT
lin.
wID
activate
the
Interface
for that unique
drive.
See
figure
2-4
for the jumper
locations.
.
2.2.2 Direction
10
This
signal
defines the direction
of
motion
of
the read/write heads when
the
STEP
bne
Is
pulsed.
An
open ctrcult,.
or
logical
false.
defines
the
direction
as "out" and a pulse applied
to
the
STEP
lin.
wID
move the R/W head
away
from
the
center
of
the
disk.
Uthe Input is shorted to ground
(logical
true)
and a
pulse
is applied, the heads
wID
move
toward
the center
of
the
disk.
I.e. ''In.
,.
2.2.3
Step
This
line
causes the read/write heads
to
move In the direction
defined
by
the
DIRECTION
IN
line. The
motion
Is
in-
itiated
at
each
logical
true-ta-false transition.
Any
change
In
the
DIRECTION
IN
line
must
be
made before the
leading
eige
of
the
STEP
pulse. Stepping can
be
performed
in
lither
the
normal or buffered mode:
Normal
Step
Mode
In
this
mode.
the
read/write heads
will
move at the rate
of
the
Incoming
STEP
pulses. The minimum
time
between
successive steps is 3.0 msec, with a minimum pulse
width
of
500 nsec. See
figure
2-5.
)
"'
•
~
1'00
,nslC
MIN'
1
~1oon"CMIN
-DIRECTION
I
I
~I
I-
3.0maec MIN
)
-STEP
J
I
I
(5141215T5OI
TYPE
UO)
-SEEK
COMPLETE
--.,
p550nsecTYP
~·'3-A
*
FIGURE
2·5.
NORMAL
STEP
MODE
Buffered
Step
Mode
In
this
mode, the
STEP
pulses are received at a
high
rate and buffered
Into
a counter.
After
the
last
STEP pulse. the
read/write heads
will
begin
stepping the desired number
of
cylinders and
SEEK
COMPlETE (refer
to
paragraph
2.4.5)
will
go
true after the heads settle on the cylinden.
This
mode
of
operation is automatically selected when the
time between
STEP
pulses is
less
than 200
pee.
. .
The
DRIVE
SElECT
line
may
be
dropped and a different
drive
selected 500 nsec after the
last
STEP pulse has
been sent to the drive.
The
maximum
time between steps is 200 1d8C. with a
minimum
pulse
width
of
3.0
~.
See
figure
2-6.
)
2·4