Roland MT-32 Owner's Manual page 33

# Data
set
1
The
size
of Ihe
requested data does not
indicate
the number
of bytes thai will
make
up
a
DTI message,
btii
represents
the
address
fields
where the requested dais
resides.
Same
models
are subject to limitations
in
data format used
for
a
single transaction.
Requested
data,
for
example, may
have a
limit in
length or
must be divided
into
predetermined
address
fields
before
it
is
exchanged across the
interface.
*The same number
of
bytes comprises address and
size data,
which,
however, vary with
the
Model -ID.
*The
error
checking process uses a
checksum
thai provides
a
bit
pattern
where
the least significant
7
bits
are zero
when
values for
Bn address,
size,
and
that
checksum
are
summed.
DT1 (12H)
This
m
e
ssage corresponds
to
the actual data
transfer process.
Because every byte
in
the data
Is
assigned a unique
address,
a
DTI message can convey
the starting address
of
one
or
more
data as well
as
a series of data formatted
in
an address
-
dependent
order.
The MIDI standards
Inhibit
non-real
time messages from
interrupting
an exclusive one. This
fact
is
inconvenient
for the
devices that support
a
"soft
-through" mechanism. To
maintain
compatibility
with such devices, Roland has
limited
the
DTI
to
2S6
bytes so that
an
excessively long
message
is
sent out
in
separate segments.
Device (A)
Device (B)
Byte Description
FOH
Exclusive
41H
Manufacturer
ID (Roland)
DEV
Device
ID
MDL
Model
ID
12H
Command
ID
as
H
Address
MSB
LSB
dc
H Da
a
SL
m
Chf ck
sum
F7H End
of exclusive
*A
DTI
message
is
capable
of providing only the
vaiid data
among
those specified
by an RQJ
message.
Some
models
are subject to limitations in data format used
for
a single transaction. Requested
data, for example,
may
have
a
limit
in
length or must
be divided
into predetermined
address
fields
before
It
is
exchanged
across the
interface.
The
number
of bytes comprising address
data varies
from
one Model -ID
to
another.
The
error
checking process uses a checksum
that
provides
a bit
pattern
where
the least significant
7
bits
are zero
when
values for
an address,
size,
and
that
checksum
are
summed.
#
Example
of
Message
Transactions
•
Device A sending
data to
Device B
Transfer of a DTI message
is
all that takes
place.
Device (A)
Device
(B)
[Data
set I]
<
*-
More
than
20m
sec
time internal.
[Data
set
1]
*-
[Data
set
1]
[Data
set 1]
«
[Data
set I] •»-
More
than
20m
sec
time internal,
[Data set I]
:
**•
-{Request data}
[Data set
1]
Handshake-
Transfer Procedure
Handshaking
is
an
interactive process
where two
devices
exchange
error checking
signals
before
a
message
transaction
takes place, thereby increasing data
reliability.
Unlike
one-way
transfer
that inserts
a pause between message
transactions,
handshake
transfer allows
much
speedier transactions
because
data
transfer starts
once
the receiving device returns a ready
signal.
When
it
comes
to
handling large
amounts
of data
—
sampler
waveforms and
synthesizer tones
over
the
entire
range,
for
example-
-across
a
MIDI
interface,
handshaking
transfer
is
more
efficient lhan
one-way
transfer.
Types
of
Messages
Message
Command
ID
Want
to
send
data
WSD
(40H)
Request data ROD
(4JH)
Data
set
DAT
(42M)
Acknowledge ACK
(43H)
End
of data
EOD
(45H)
Communication
error
ERR (4EH)
Rejection
RJC
(4FH)
#
Want
to send
data
:
WSD
(40H)
This message
is
sent out
when
data
must
be sent
to a
device
at
the other
end
of the
interface.
It
contains
data
for the
address and
size that specify designation
and
length
respectively,
of the data
lo
be senl.
On
receiving a
WSD
message,
the
remote device checks
its
memory
for
the specified
data address and
size
which
will
satisfy the request,
if
it
finds
them and
is
ready
for
communication,
the
device
will return
an "Acknowledge
(ACK)"
message.
Otherwise,
it
will return a "Rejection (RJC)" message.
Byte Description
FOH
Exclusive status
41H
Manufacturer
ID
(Roland)
DEV
Device
ID
MDL
Model
ID
40H
Command
ID
aaH Address
MSB
LSB
SsH
Size
MSB
LSB
sum Check sum
F7H End
of exclusive
•
Device B
requesting data from Device
A
Device
B
sends an RQJ message
to
Device
A.
Checking
the
message, Device
A
sends
a
DTI
message back
to
Device
B.
The
size
of the data
to be sent
does
not indicate the
number
of
bytes that
make up
a
"Data
set
(DAT)"
message, but
represents
the
address
fields
where
the data should reside.
Some
models
are
subject to limitations in data
format used
for a single transaction.
Requested
data, for
example,
may
have a
limit in
length or must be divided
inlo
predetermined
address
fields
before
it is
exchanged
across
the
interface.
The same number
of byles
comprises address and
size
data,
which, however, vary
with the
Model -ID.
*The
error checking process uses a checksum
that provides
a
bit
pattern
where
the
least
significant 7
bits
arc zero
when
values
for
an
address,
size,
and
that
checksum arc summed.