Roland MT-32 - Page 34

#
Request
data RQD (41
H)
This message is sent
uul when there is
a need to acquire data
from a device
at
the
other
end
of the
interface. It contains data
/or the address
and size
that specify
designation and length,
respectively,
of
data required.
On receiving
an
RQD
message, the remote
device checks its
memory for the
data
address and size
which saltsfy the
request,
If it finds them
and is ready
for
communication, the device
will
transmit a "Data
set (DAT)"
message, which
contains the
requested data.
Otherwise, it
will return a "Rejection <RJO"
message.
Byte
Description
FOH
Exclusive
status
4!H
Manufacturer ID (Roland)
DEV
Device ID
MDL
Mode!
ID
41H
Command ID
aaH
Address
MSB
LSB
ssH
Size
MSB
LSB
sum
Check sum
F7H End
of exclusive
#
Data set
*The size of
the requested
data
does not
indicate the number
of bytes thai
make up a
"Data set (DAT)"
message,
hut
represents
the address
fields
where the requested
data
resides.
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 same
number of
bytes comprises
address and size
data,
which, however,
vary with the
Model -ID.
•The
error checking
process
uses a checksum
that provides
a bit patlern
where the
least significant
7
bits
are zero when
values lor an
address, size,
and that checksum
are
summed.
DAT
(42H)
This message
corresponds to the actual
data transfer process.
Because
every byte in
the data is
assigned a unique
address,
the
message can
convey the starting
address of one or more
data as
well as a
series of
data formatted in an
address-dependent
order.
Although the MIDI
standards
inhibit non-real
time
messages
from interrupting an
exclusive one, some
devices support a
"
soft- through
"
mechanism
for such
interrupts
.
To
maintaincompattbility
with such
devices, Roland
has limited the
DAT to 2S6bytes so
that an
excessively long
message is sent
out in
separate
segments.
Byte
Description
FOH
Exclusive status
4?H
Manufacturer ID (Roland)
DEV
Device ID
MDL
Model ID
42H
Command
ID
aaH
Address MSB
LSB
ddH
Data
sum
. Check
sum
F7H
End
of exclusive
#
Acknowledge
*A
DAT
message
is
capable of
providing only the
valid
data
among
those
specified by an
RQD or
WSD
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 interlace.
•
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.
ACK <43H)
This
message is
sent out
when no
error was
detected on
reception of a
WSD, DAT,
"End of data
(EOD)",
or some other
message
and a
requested
setup or action is
complete. Unless
it
receives an
ACK
message, the
device at
the other end
will
not
proceed
to the
next operation.
Byte
Description
FOH
Exclusive status
41H
Manufacturer ID
(Roland)
DEV
Device ID
MDL
Model
ID
43H
Command
ID
F7H
End of
exclusive
#
End of data
EOD
(4SH)
This
message is senl out to
inform a
remote
device of the
end
of
a message.
Communication,
however, will not
come to an
end unless
the
remote device returns
an
ACK message
even
though an
EOD
message was
transmitted.
Byte
Description
FOH
Exclusive status
41H
Manufacturer
ID (Roland)
DEV
Device ID
MDL
Model ID
45H
Command
ID
F7H
End
of exclusive
#
Communications
error :
ERR
(4EH)
This
message warns
the remote
device of a
communications
fault
encountered
during message
transmission
due,
for
example, to
a
checksum error. An
ERR
message may
be
replaced with a
"Rejection (RJC)"
one,
which
terminates the
current
message
transaction in
midstream.
When it
receives
an ERR
message, the
sending
device may
either attempt
to send out
the last message
a second
time or
terminate
communication by sending
out an RJC
message.
Byte
Description
FOH
Exclusive
status
41H
Manufacturer
ID
(Roland)
DEV
Device ID
MDL
Model ID
4EH
Command ID
F7H
End
of exclusive