Yamaha tx7 Service Manual page 12

TX7
CONSTRUCTION OF THE TX7
You may
think
of the
TX7
as a
DX7
without the sub
CPU,
that
is
to
say,
a
DX7
without the
keyboard
section.
The
circuitry of the
TX7
is
on four boards;
DM, AS, PN, and
AD
.
The
DM
board contains the
micro
computer which controlls
the
FM
tone
generator, pane! switches,
MIDI and the LCD.
The
AS
board
contains the
FM
tone generator. Its
EGS
and
OPS
(the
same
ICs as the
DX7) are controlled
by the
MPU.
The
PN
board
contains the panel switches.
The
MPU
on the
DM
board
is
constantly
checking to see
if
any
of these
switches are
being pressed.
The
AD
board contains the
power supply.
To make
it
light
and compact,
we
have used
a switching
power supply of the
RCC
(Ringing
Choke Con-
verter) type.
1.
Memory map
The
memory map
of the
TX7
is
shown below.
$0000
MPU
internal registers
$001
F
Free area
$0040
MPU
internal
RAM
$OOFF
Free area
Panel switches
$4800
VCA
control
EGS
$5800
OPS
RAMI
$6800
RAM2
$7000
RAM3
$7800
RAM4
$7 F F
F
Free area
vPUUUU
$FFFF
ROM
1)
Voice and function memory, and edit buffers
The data
in
RAMI
,
2,
3
is
as follows.
$601
E-
$701 D
:
32 voice data
$701 E
~
$70B8
:
Voice edit buffer data
$70C9
~
$72C8
:
32
TX
function data
$72C9
-
$74C8
:
32
DX
function data
$74C9
~
$74
DA
:
Function edit
buffer data
Here
is
a
comparison of the data format with the
illustra-
tion
on page
1
.
Since the master tune data
is
common
to
all
32
voices,
there are
2
additional bytes beside the 17 bytes
in
the func-
tion edit
buffer.
(When
the
DX
performance parameter
MASTER TUNE
is
sent via
MIDI,
it is
only
1
byte. However,
since
the
TX
internal
tuning data
uses
14
bits,
2 bytes of
memory space are needed.)
The
format of each
memory
is
as follows.
• Voice
edit
buffer data ••
-155
bytes
Format
is
the same as
DX
voice
parameter change
perameter
numbers 0
—
154. See
MIDI
data
format 4-1.
• 32
voice data
••128
bytes x
32 * 4 K
bytes
Format
for
each voice
is
the same
as
the voice edit buffer,
but
155 bytes of data
is
packed into 128 bytes of
memory
space.
(Unused
bits
are
moved
over.)
•
Function edit buffer data
••17
bytes
Format
is
the
same
as
MIDI data format 4-2
(DX
perfor-
mance parameter change) parameters 2 -- 7, 9
—
16, 26.
These 15 bytes plus
the 2 bytes Key Limit
Low
and
Key Limit High
make up the
total
of 17
bytes.
• 32
TX
function data *--17 bytes x
32 = 544 bytes
Format
for
each function
is
the
same
as
the function
edit buffer.
(When saving data to tape, attenuation
data will
not be
saved.)
• 32
DX
function data
-*-16 bytes x 32
= 512
bytes
Format
is
the
same
as
MIDI data format 4-2
(DX
per-
formance
parameter chenge) parameters 2
~
7,
9
~
16.
These
14 bytes plus the 2 bytes Key Limit
Low
and
Key
Limit High
make up
the total
of 16
bytes.
2.
Circuitry
of the
TX7
1)
MPU (HD63A03X)
The TX7's
MPU
is
the
same
as
that of the
TF1 (tone
generation
module for the
TX816). The
MPU
contains an
AC
I
A
(Asyncronous communication
unit), I/O ports
s,
and
RAM.
The
ACIA
transmits and receives
MIDI messages,
and the I/O ports check the condition of
the switches and
send information to the
LCD.
• Vcc, Vss Vcc
is
the
SV power
supply
terminal, Vss
is
the ground terminal.
•
EXTAL
This receives a
4.71
Mhz
clock with
a
50%
duty cycle. (Since an external clock
is
used,
the
XTAL
terminal
is
left
open.)
•
MP
0
,
MPj
This sets
the operation
mode
of the
MPU.
MP
0
= "High",
MP
X
*
"Low".
• RES
This terminal resets the
MPU.
•
STBY
This terminal
is
for setting the
MPU
to Stand-
by mode, but since
it is
not used in this
circuit, it
has been fixed
at
"High".
• NMI This terminal
if
for non-maskable interrupt,
but since
it is
not used
in
this circuit,
it
has
been fixed at
"High".
•
Port
Z
In this circuit,
P
20
-
P 27 are
used
as
follows.
P20
(out)
Transmission
to cassette.
Transmission speed:
1200 band (1200Hz
-
1
cycle
"0", 2400
Hz
—
2
cycle "1
"),
modulation:
FSK.
Data
is
compatabie with the
CX5 (YRM-1
3).
(However, the
YRM-1 3
will
not accept
Key
Limit or Attenuation data.)
P21
(
)
Not
used.
-
22
-
TX7