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~li"(1D[QJ~1R3
External I/O ports
The
~icroprocessor
scans the keyboard
via
the
outputs
P~Q
...
P05
and the
inputs
P10
P14 (IC1, IC16, I(23)
.
The signals RE,
RP and TL-FIL supply information on
t~e
position of the laser pIckup.
~ith
SI the microprocessor
invokes
a
start-up procedure;
the \aser diode and
the
focus control circuit are enabled.
The outputs
80
.
,.
83 (IC18) control the radial
control
circu1l,
and the MUSB signal mutes all outputs in search
mode. With ATS8 the output level is decreased
by
1Z dB.
With its outputs (DLEN-1, DLEN-Z, DATA and eLK) le17 con-
trols the driver components of the LC display.
The SYNC signal Is "L" when the CO player is synchronized
to an external reference 1requency (SLAVE mode).
Tne
signals
for the
indicators
of the
parallel
remote
control are decoded by
IC22
and buffered by lC21,
except
{or
the signals EN
01
and
EN 02
with which the
PARALLEL
CONTROLLER
reads time,
index,
and track data from
the
bus.
3.2.2
Signal processor
-) FIg. 3.5
From
the
four pho(odiode currents
(Al
A4),
the
signal processor (Ie}) produces the radial-error
signals
~El
and REZ for the radial-error control in IC2,
as
~ell
as the focus control signals FE and FE LAG
.
3.2
.
3
Oisc
motor control
-> Fig.
3.5
In
order to keep the stream of data from
CO
as
steady
as possible,
it
is necessary to control
the
speed of the
disc.
Oepending on the position of the laser pickup, toe
circumferential
speed of the scanned track is set to 1.2
or 1 4 m/s.
The MSC speed correction signal is generated
in
the decoder (Iel0 on OECODER BOARD
1.769
.
430).
T01S
pulse wldth modulated signal has a duty factor of approx-
1mately SOX in play mode; during the start phase (accele-
ration
of the disc) it reaches
98X
for approx
.
0
.
2
se-
conds
.
In
IC15,
the signal is shaped into the VC
disc
motor
control signal by means 01 an amplifier
with
PIO
characteristic
3.2.4
Radial control
-) Fig.
3.5
Since
the
laser
pickup
must be able to fOllow the track
on
the disc,
the pickup
is
equipped with
a
rotary
arm,
the
drive
of which
is
designed like a moving
coil
in-
strument.
The
two radial-error sIgnals RE1 and RE2
are
amplified
and
decoded in IC2
.
The subsequent
LEAD/LAG
power amplifier (Ie7) controls the radial
motor
.
Offset
alignment is possible with the trimmer potentiometer R62
.
The value of the radial-error signal RE produced from the
signals RE1 and RE2 in
1(2,
is composed according to the
following formula:
RE
=
k-d(ll
+
12
~
13
+
14)
-k(Il
+
12)
IIhere:
R€ " radial-error sIgnal
k
=
factor 01 the phase comparison ;n lC2
d
=
factor of the offset control circuit in lC2
11 to 14
=
currents of the receiver diodes A1 to A4
RE1
=
11
+
1'2
RE2 "
n
+
14
A727
~'"~~~~liT-<~.
' ' '
==
,III
I
~"
" ,
-~'
~ ~'n
'
tl
.t-
~
~
,~
~.
'l!J
. j
'0\.,...'
=
~
r,
n
~
!;
. . "
E
~-j
I
I
•
K'
.
I [
~'t~H
(I-oI
I:
"'HID
';0..,1
- '
'~'"
I
I
I
I
Fig.
3.5
,~...
~.T
n:
·
l~~_kA
.
E 3/5
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