BASF 6106 - Page 26

2.2.5.
TRACK
ZERO
DETECTOR
This
logic
generates
the
TRACK
00
signal
when
the
read/write
head
is
positioned
at
track
zero.
The
host
systea
uses
this
signal
to
recalib-
rate
the
positioning
syste».
When
the
posi-
tion
of
the
read/write-
head
is
unknown
the
host
systea
sends
step
out
pulses
until
TRACK
00/
goes
low.
The
track
zero
detector
coaprises
a
aicro-
switch,
a
debounce
circuit
and
a
phase
coa-
parator
circuit
(see
Fig.
2-21
)
and
is
activated
by
the
head
carriage.
When
the
head
carriage
noves
but
the
track
zero
switch
aust
be
open
before
the
read/write
head
reaches
track
four.
When
the
head
carriage
acnes
to-
wards
the
track
zero
position
the
microswitch
aust
close
after
track
four
and
before
track
zero.
The
TRACK
ZERO
signal
will
be
active when
the
track
zero
switch
is
closed
and
phase \
and
phase
C of
the
stepper
motor
are
vated.
OUTENABLE
(0
ENA)
must
be
high.
g
2-22
shows
the
corresponding
timing
gram
when
the
host
system
tries
to
step
the
head
carriage
out
of
track
zero.
The
mechani-
cal
stop
at
the
spiral
wheel"
prevents
the
read
/
write
head
from
moving
out
further
and
holds
it
near
track
zero.
The
TRACK
00/
signal
will
be
deactivated,
because
the
stepper
motor
is
in
a
wrong
phase
(0
B
and
C).
If
the
host
system
sends
three
more
step
out
pulses,
the
phase
of
the
stepper
motor
is
correct
again,
the
TRACK
00
signal
is
again
activated
and
the
read/write
head
is
positioned
at
track
zero.
TRACK
00
SWITCH
NO
NC
5V
>:•:
OUTPUT
INTERFACE:::::;:
FROM
STEPPER
P/Jb
MOTOR
CONTROL
\
T
-
HUS'1
*
T
°
fHt
SYSTEM
TROM
INPUT
INTERFACE
*-
OENA
FIGURE 2
-
21
. TRACK ZERO DETECTOR
FIGURE
2
-
22 . TRACK
ZERO
-
TIMING
DIAGRAM
16