Roland U-20 Owner's Manual page 182

#
Request
data
ROD
(41 H)
This message
is
sent out
^len
there
is
a need
to
acquire
data
frcm a device
at
the other end
of the interface.
It
contains data
for the address
and
size
that ^lecify
d^lgnatlon and
length,
respectively, of data required.
On
receiving
an
ROD
message,
the
remote device
checJcs
its
memory
for the data address
and
si2s
which
satisfy
the request
If it
finds
them and
is
ready
for
communication, the devit^
will
transmit a "Data
set
(DAT}'
message,
which contains the
requested
data. Otherwise,
it
will return a
"Rejection (RIC)"
messa^.
Byte Descriotron
FOH
Exclusive status
4IH Manufacturer
ID (Roland)
DEV
Davica
ID
MDl
Model
ID
41
Command
ID
asH Address
MSB
!
LSB
ssH Size
MSB
i
L 3B
sum Check
sum
F7H End
of exclusive
#
Data
set
nThe
size
of the requested data does not indicate the
number
of bytes that
make up
a "Data
set
(DAT)" message, but
remesents the address fields
where the requested data
resides.
*Some
models are subject
to limitations in
data fonnat 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 pnx^ss uses a
checksum
that
pw/ides
a
bit
pattern
where
the least significant 7 bits are zero
when
values for
an
address,
size,
and that
checksum
are
summed.
DAT
C42H)
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 BB well as a series of
data formatted
in
an address
dependent
order.
Although the
MIDI
standards
inhibit
non -
real
time
m^sages
from
interrupting
an
exclusive one.
some devices support a
"soft
-
through'
mechanism
for
such
interrupts.
To
maintain
compatiUiity
w^th sudi
devices,
Ridand has
limited
the
DAT
to
256 bytes so that an excessively
tone message
is
sent
out
in
separate segments.
Byte
Description
FOH
Exclusive status
41
Manufacturer
ID (Roland)
DEV
Device
ID
MDL
Model
ID
42M
Command
ID
asH AddresB
MSB
Lsa
d
H
Data
81.
m
i
i
Check
sum
F7H £nd of exclustva
*A
DAT
message
te
capable of providing only the valid
data
among
those
^lecified
by
an
RQD
or
WSD
message.
*Some
models are subject to limitations in
data format used
for a single hansaction.
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 compiling address data
varies
from
one model ID to another.
*<The
error
checking process uses a
checksum
that provide;
a
bit pattern
where
the least slsnificant
7
bits
are zero
when
values for
an address,
size,
and
that
checksum
are
summed,
#
Acknowledge
:
ACK
(43H)
This
message
is
sent out
when no
error
was
detected
on
reception of a
WSD, DAT, "aid
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 (^ration.
Byte Description
FOH
Exclusive status
45
H
Manufacturer
ID
(Roland)
DEV
Device
ID
MDL
Model ID
43H
Command
ID
F7H End
of exclusive
#
End
of data
:
EOD
C45H)
This message
is
s«it out to
infmm
a
remote
device of the enc
of a
message. Communication, however,
will
not
come
to
an enc
unless the
remote device returns an
ACK
message even thaug^
an
EOD
message
was
transmitted.
Byte Description
FOH
Exclusive status
41
Manufacturer
ID (Rolend)
DEV
Device ID
MDL
Model
ID
45H Command
ID
F7H End
of Bxoluaivo
#
Communications
error
:
ERR (4EH)
This message warns
the
remote device of a communication!
fault
encountered during message transmission
due
,
foi
example, to
a checksum
error.
An ERR
message
may
ix
replaced with a
'Rejection
(RJC)"
one,
which
terminates
th(
current
message
transaction
in
midstream.
When
it
receives
an
ERR
message,
the
sending device mas
either attempt
to
send out the
last
message a second time
oi
terminate
aimmunication by sending out
an
RJC
message.
Byte
Description
FOH
Exclusive status
41
Manufacturer
ID
(Roland)
DEV
Device ID
MDL
Model
ID
4EH
Command
ID
F7H
End of exclusive
180