Roland U-20 Owner's Manual page 181

#
Data
set
1
*The
size
of the
requested data does not
indicate the
number
of bytes
that will
make
up a
DTI
message, but represents
the address
fields
where
the requested data
resides.
fSome
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
predetmnined
address
fields before
it
is
exchanged
across the interne.
*he same
number
of bytes comprises addre^ and
size
data,
which, however, vary with the
Model
-
ID.
The
error checking
process uses a
checksum
that provides
s
bit
pattern
where
the
least significant
7
bits
are zero
when
values
for
an
address, ^ze, and
that
checksum are summed.
DTI
(12H)
This
message
corresponds
to the actual data transfer process.
Because every
byte
in
the data
Is
assigned
a unique
address,
a
DTI message
can
amvey
the starting address of
one
or more
data as well as a
series of data formatted
in
an address
-
depoident
order.
The
MIDI standards
inhit^t
non
-
real time
messages from
interrupting
an
exdurfve one.
This fact
is
inconvenient
for
the
devices
that
support a
"soft
-
through" mechanism.
To
maintain
compatibility with such
devices,
Rdand
has limited the
DTI
to
256 bytes so
that
an
excKsively long
messa^
is
sent out
in
separate segments.
D»ncB
(A)
Device
(B)
Byte
FOH
41H
DEV
MDL
12H
aaH
ddH
sum
F=7H
Description
Exciuaive
Manufacturer
ID CRoland)
DB\rice ID
Mode! ID
Commend
ID
Address
MSB
i
LSB
Date
Check
sum
End of exclusive
«A
DTI
message
is
capable
of providing only the valid data
among
those specified by an
RQl
message.
*Some
models are sutdect
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 {Redetermined
address
fields before
it
is
exchanged across the
interface.
The
numbw
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
tiits
are zero
when
values
lor an address,
siie,
and
that
checksum
are
summed.
#
Example
of
Message
Transactions
#Device A
sending data
to
Device
B
Transfer of a DTI message
!s all
that takes place.
Dovioe (A)
Device
CB)
[Data aat
1]
^
* More
ttian
20m
sec time
Intornai,
[Data
set
1]
^
[Data set
1]
IDevIce
B
requesting data from Device
A
Device
B
sends an
RQl
message
to Device A.
Checking
the
message. Device
A
sends a
DTJ
message back
to
Device
a
[Data set
1] -^
[Data
set
1]
^
* More
than
20m
bbc
time internal.
[Data set
1]
^
[Raguest
data]
[Date set
t]
Handshake
~
Transfer Procedure
Handshaicing
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 tietween message
transactions,
handshake
transfer
allows mudi
speedier transactions because
data
transfer starts
once
the reviving device
returns a ready
signal.
When
it
comes
to handling large
amounts
of
data
- -
sampler
wavefomu
and
synthesizer tones over the
entire
range, for
example
- -
across a
MIDI
interface,
handshaking
transfer
is
more
efficient
than one
- way
transfer.
Types
of
Messages
Messes
e
Command
ID
Want
to send date
WSD
C40H)
Request
date
HOD
(41
H>
Data
set
DAT
C42H)
AcknowledQB
ACK
C43H)
End of data EOD
C45H)
Communication
error
ERR
C4EH)
Rejection RJC
C4FH)
# 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
respectivdy, of the data
to
be sent
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
devfa:e will return an
"Acknowledge
(ACK)"
message.
Otherwise,
it
will return a
"Rejection
(RJC)" message.
Byte
Description
FOH
Exclusive status
41 Manufacturer
ID (Roland)
DEV
Device
ID
MDL
Model
ID
40H Command
ID
asH
Address
MSB
LSB
BSH
j
Size
MSB
[
\
LSB
sum
Check sum
F7H
End
of exclusive
The
size
of the data
to be sent does not indicate the
number
of bytes that
make
up a 'Data
set
(DAT)"
message, but
represenU
the address
fields
where
the data should
reside.
Some
models
are subject
to limitations in
data
format used
for
a
single transactkin. 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,
whlcti. 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
an
address,
size,
and
that
checksum
are
summed.
179