Roland JV-80 - Page 198

Roland Exclusive Messages
*
The
size of the requested data does not indicate the
number
of
bytes
that
will
make up a DT)
message, but represents the address fields
where the requested data resides.
*
Some models are subject (o
limitations in data format used for a
single transaction. Requested data, for example, may
have
3 limit
in
length or must tie 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 thai
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 1
:
DTI (12H)
This message corresponds to the actual data transfer process.
Dccause
every byte in the data is assigned a unique address, a DTI
message can
convey
the starting address of one or more data as
well
as a series of data formatted in an address- dependent order.
The
MIDI standards inhibit non-real time messages from Interrupting an
exclusive
one. This fact is
inconvenient
for the
devices that support a
"sofl-through" mechanism. To maintain compatibility
with
such
devices.
Roland has limited the DTI to 256 bytes so that an
excessively
long
message is sent out in separate segments.
•
Device
B
requesting data from Device A
Device
B sends an RQl message
to Device
A.
Checking
the
message. Device
A
sends a
DTI
message back to Device
B.
Device (A) Device
(8)
[Data s«t
1]
-^
[Request data]
[Data
set
1]
^-
« More than 20m sec time internal.
[Data set 1]
;
*-
[Data set
1J
'
^-
Byte Desor lotion
FOH
Exclusive
41H
Manufacturer ID (Roland)
DEV Device ID
MDL
Model ID
12H Command ID
aaH Address MSB
LSB
ddH Data
sum Check sum
F7H
End of exclusive
*
A DTI message is capable of providing only the
valid
data among
those specified by an RQJ
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 l>e 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 thai
provides
a bit
piittcrn where the least significant 7 bits are zero when
values
for
an address, size, and that checksum
are summed.
#
Example of Message Transactions
*
Device
A
sending
data
to Device
B
Transfer
of
a DTI message is all that takes place.
Device
(A)
Device
(B)
[Data set
I)
^-
* More than 20m
sec
time internal.
[Data set 1]
[Data set
1]
198