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Fostex A-8 - 4. Control Circuit Functions; System and Peripheral LSI Circuits

Fostex A-8
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4.
FUNCTION
OF
THE
CONTROL
CIRCUITS
4.1
SYSTEM
CONTROL
CIRCUITS
Control
signals,
which
are
the
foundation
of
tape
transport
operation,
are
processed
by
the
TTL
type
LSI,
U9.
In
the
System
Control
of
this
Unit,
the
U9
output
pins
for
PLAY,
STOP,
F.FWD,
REWIND,
REC
and
BRAKE
are
used
in
the
various
control
circuits,
and
when
a
low
level
is
input
to
the
pin
corresponding
to
the
output
for
that
function,
a
low
level
is
obtained
at
that
output
pin.
4.2
PERIPHERAL
CONTROL
CIRCUITS
OF
THE
LSI
1)
CR
1
(U9-5)
This
is
the
reset
signal
input
pin
of
U9.
At
switch
on
of
power,
U9-5
goes
to
"L"
level
for
the
length
of
time
that
Qi
is
on,
thus
resetting
U9.
When
power
is
switched
on,
C21
begins
to
be
charged,
during
which
time
the
base
of
Ql
goes
to
"H"
,
thus
switching
on
QI.
When
C21
becomes
fully
charged,
the
base
of
Ql
goes
to
"L"
,
thus
switching
off
Ql.
When
power
is
switched
off,
C21
is
quickly
discharged
through
D38
and
thus
be
comes
ready
for
the
next
switch
on
of
power
.
2)
EBR
IN(U9-4)
In
this
system,
brake
is
applied
electrically
from
REWIND
or
F.FWD
before
final
ly
going
into
the
STOP
mode.
For
p
vam
ple,
if
the
STOP
button
is
depressed
during
REWIND,
the
transport
tem
porarily
goes
into
F.FWD
mode
and
then
into
STOP
mode
when
an
"L"
level
is
ap
plied
to
this
EBR
IN.
For
timing
of
"L"
level
application
to
EBR
IN,
refer
to
Tape
Counter
Detecting
Circuit
and
Motion
Sensing
Circuit
(Item
4.7).
3)
EDIT
The
"L"
level
signal
from
the
EDIT
switch
when
it
is
set
to
IN
is
not
only
ap
plied
to
Qll,
which
is
the
circuit
to
stop
the
takeup
reel
(right
side)
motor
(Refer
to
Item
4.6)
but
also
to
the
exclusive
OR
gate
U2-2.
When
the
EDIT
switch
is
set
from
OUT
to
IN,
an
"L"
level
is
applied
to
U2-2
and
as
02-13
is
also
at
"L"
,
output
U2-11
goes
to
"L"
and
as
this
is
applied
to
U9-6,
U9
goes
to
the
STOP
mode.
In
the
meantime,
the
input
to
U2-12
will
go
to
"H"
level
after
a
certain
delay
introduced
by
the
integration
circuit
of
R12
and
C3,
and
output
pin
U2-11
goes
to
"H"
level.
One
"L"
level
pulse
is
output
from
U2-11
when
the
EDIT
switch
is
set
from
IN
to
OUT.
11

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