# Request data :
RQD
(41 H)
This message is sent out when there is a need to acquire
data
from a device
at
the other end of the interface. It contains
data
for 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 satisfy 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 (RJC)"
message.
Byte
Description
F0H
Exclusive
status
41H
Manufactures
ID
(Roland)
DEV
Device
ID
MDL
Model
ID
41H Command
ID
aaH Address
MSB
LSB
ssH Size
MSB
LSB
sum Check sum
F7H
End of exclusive
* The size of the requested
data
does not indicate the number
of bytes that make up a "Data set (DAT)" message, but
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 pattern where the least significant 7 bits
are
zero when
values
for
an
address,
size,
and
that
checksum
are
summed.
# Data set : DAT (42H)
110
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
maintaincompatibility with such devices, Roland has limited the
DAT
to 256bytes so that an excessively long message is sent
out
in
separate
segtnents.
Byte Description
F0H
Exclusive status
41H Manufactures
ID
(Roland)
DEV
Device
ID
MDL
Model
ID
42H
Command
ID
aaH
Address
MSB
LSB
ddH
Data
:
sum
Check
sum
F7H
End
of exclusive
*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 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.
# Acknowledge :
ACK
(43H)
#
End
of
data
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
F0H
Exclusive status
41H
Manufactures
ID
(Roland)
DEV
Device
ID
MDL
Model
ID
43H Command
ID
F7H
End
of
exclusive
EOD
(45H)
This message is
sent
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
F0H
Exclusive status
41H Manufactures
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
F0H
Exclusive status
41H
Ma':'ufactures
ID
(Roland)
DEV
Device
ID
MDL
Model
ID
4EH
Command
ID
F7H
End
of
exclusive
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