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Korg EX-8000 - Main Circuit Explanation; Oscillator and Sound Generation

Korg EX-8000
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5.
Main
circuit
explanation
The
EX-80Q8>is
a
programmable
synthe
module
can
be
con
nected
to
MIDI
keyboards
and
other
MIDI
devices.
The
DWGS
used
is
the
same
as
for
the
DW-8000
and
adjust
ments,
etc.,
are
also
the
same.
A
Simple
Explanation
Using
MIDI
Note
Data
as
an
Exam
ple.
When
note
data
are
input
from
the
MIDI
IN
terminal,
they
enter
port
23
of
the
CPU
(63B03X)
through
the
photo
coupler
(TLP-552)
and
are
then
output
as
16-bit
data
(PAI
data
or
wave form
data)
by
the
system
program
of
IC38
(HN4827128).
These
data
are
input
to
IC60
(MB62H133)
together
with
j>-bit
addresses.
A
WRITE
signal
is
output
from
the
PAI
W
terminal
of
IC60,
and
the
PAI
data
are
stored
in
IC51,
53,
55,
57
of
74LS189.
Wave
form
data
are
stored
in
IC49
by
a
WRITE
signal
from
the
WF
W
terminal.
In
the
same
way,
PAR
data
are
stored
in
IC48,
50,
52, 54,
56
by
a
WRITE
signal
from
the
PAR
W~terminal.
These
data
are
called
out
by
a
PAR
S
and
PAI
S~READ
signal,
are
added
at
IC60
and
output
as
18-bit
data.
DB7
—
DB18
contained
in
these
data
are
input
to
IC47
(MB64H129)
together
with
octave
select
data
(Oct
0
-
Oct
2).
At
the
same
time,
these
18-bit
data
are
stored
in
IC48,
50,
52,
54,
56
as
PAR
data
and
are
again
added
to
the
PAI
data.
The
data
output
from
IC60
are
decoded
by
IC47
(MB-
62H129),
are
input
as
WAVE
TABLE
addresses
to
a
WAVE
TABLE
ROM
selected
by
CS.
The
wave
form
data
specified
by
these
addresses
are
output
as
DO
—
D7
8-bit
data.
These
data
are
wave
formed
by
D/A
convenor
IC42
(DAC08)
and
are
output
through IC41
(NJM5534).
See
the
section
below
concerning
oscillator
operation.
Oscillator
operation
The
PAI
(phase
angle
increment)
value
and
PAR
(phase
angle
register)
value
are
added
and
the
result
is
stored
again
in
the
PAR.
The
PAR
value
is
used
as
the
wave
table
ad
dress.
The
wave
table
stores
different
harmonic
configura
tion
data
for
each
octave
on
the
keyboard.
IC47
(MB64H129)
performs
the
processing
needed
to
use
the
PAR
value
as
the
wave
table
address.
Finally,
data
read
from
the
wave
table
is
converted
to
an
analog
waveform
by
a
D/A
converter.
Time
division
multiplexing
enables
dual
oscillator
6-uoice
sound
source
capability.
Maximum
simultaneous
output
of
this
system
is
8
voices
x 2
oscillators.
Note: Given
a
sampling
frequency
of
50
kHz,
PAI
data
N
*
218
x
f/50
x
103
(where
f
is
the
pitch
frequency)
is
rounded
to
an
integer
value
for
N
and
converted
to
a
hexadecimal
number.
The
main
LSI
chips
are
the
CMOS
gate
array
IC47
(MB-
64H129)
and
IC60
(MB62H133),
the wave-table
256K
mask
ROM
IC43
and
IC46
(HN613256),
the ten
TTL
64-
bit
RAM
chips
for
PAI
&
PAR
(IC48-IC57;
S189),
the
8-bit
D/A
converter
IC42
(DAC-08),
decoder
chips
IC50,
IC59
(LS244),
KLM-662
IC16
(LS175),
IC14,
IC15
(LS138),
as
well
as
S/H
analog
switches
(IC17~IC20;
4066)
and
OP
AMPS
(IC21HC25;
072).
IC60
(MB62H133)
is
a
64-pin
LSI
with
about
800
gates
handling
major
aspects
of
the
system
including
the
CPU
interface,
timing
generation,
and
adder.
CPU BUS
1
1
PAR
c
r_
c
c
[
CPUI
)
1
NTER
^
-—••
PAI
FACE
| •
•
•
1
—
ADDER
J
1
DECODER
WAVE
TABLE
D/A
S/H
|
|
1
1
•-•
...
IC6°
74LS189
x
10
IC48-ICS7
•--
IC60I62H133)
IC47
<64H129)
64KR0M
IC43~IC46
••-
DAC-08
-»
HC138
+
4066
+072
I
#
1
•i
,{
?*
1
16
OSCILLATOR
OUTPUT
1%
"1
4
-36-
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