1.4
FUNCTIONAL OPERATIONS
1.4.1
Power
Sequencing
Applying dc power to the
SA455/465
can
be
done
in
any
sequence. However, during power up, the WRITE
GATE line must be held inactive or at
4;\
high level. This
wlll
prevent possible "glitching" of the media. After ap-
plication of dc power, a
100
ms delay should be introduced
bE!fore
any operation
is
performed. After powering
on,
Initial
position of the read/write
heads
with respect to the data tracks
on
the media
is
indetermlnant.
In
order to
assure proper positioning of the
read/write
heads after power on, a
Step
Out operation should be performed until
the TRACK
00
line becomes active (Recalibrate).
1.4.2
Drive
Selection
Drive selection occurs when the propel:' DRIVE SELECT line
is
activated. Only the drive with this line jumpered
will
respond to Input lines
or
gate output lines.
1.4.3
Motor
On
In
order for
the
host system to read or write data, the dc drive motor must be turned
on.
This
is
accomplished by
activating the line -MOTOR ON. A
500
ms delay must be introduced after activating this line to allow the motor to
come
up to
speed
before reading or writing can be accomplished.
The
motor must be turned off by the
hoslt
system by deactivating the MOTOR ON line,
The
control electronics
keep the motor active for 3seconds,
aliter
MOTOR ON
is
deactivated. This allows reselectlng during copy opera-
tions
and
will
ensure maximum motor
and
media
life.
1.4.4
Track Accessing
Seeking the
read/write
heads
from
one
track to another
is
accomplished
by:
a. Activating the DRIVE SELECT line.
b.
Selecting desired direction
IUslng
the DIRECTION SELECT line.
c. WRiTE GATE being inalctive.
d. Pulsing the STEP line.
Multiple track accessing
is
accomplished by
repeated
pulsing of the STEP line (with direction valid) until the desired
track has
been
reached. Each pulse
on
the
STEPline
will
cause
the
read/
write
heads
to move
one
track either
in
or
out depending
on
the DIRECTION SELECT line.
Head
movement
is
initiated
on
the trailing edge of the step
pulse.
1.4.5
Step
Out
With the DIRECTION SELECT line at aplus logic level (2.4 to
5.25
V), apulse
on
the STEP line
will
cause the
read/write
heads
to move
one
track away from
the
center of
the
disk.
The
pulse(s) applied to the STEP line must
have the timing characteristics shown
in
'figures 1-3
and
1-4.
1.4.6
Step
In
With
the
DIRECTION SELECT line at minus logic level (0
to
0.4
V), apulse
on
the
STEP line
will
cause
the.
read/write
heads
to move
one
track
<:loser
to
the
center of
the
disk.
The
pulse(s) applied to the STEP line must
have the timing characteristics shown
in
figures 1-3
and
1-4.
1.4.7
Side
Selection
Head
selection
is
controlled via the
1./0
signal line designated SIDE SELECT. Aplus logic level
on
the SIDE
SELECT line selects the
read/write
hE!ad
on
the side asurface of
the
diskette. Aminus logic level selects
the
side 1
read/write
head.
When switching from
one
side to
the
other, a
100
p,s
delay
is
required after SIDE SELECT
changes state before a
read
or write oper,ation can be
initiatE~d.
Figure 1-5shows the use of SIDE SELECT prior to
a
read
operation.
