Roland MT-32 Owner's Manual 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