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#Request
data #1:
RQ1
(ТІН)
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 RQ]
message, the remote device checks
its memory
for the data address and size that satisfy the
request.
If it finds them and is ready for communication, the device
will transmit a "Data set 1 (DT1)" message, which contains
the requested
data.
Otherwise,
the device
will send
out
nothing.
Exclusive
status
Manufacturer
ID (Roland)
Device
ID
Model
ID
Command
ID
Address
MSB
LSB
Size
MSB
Check
sum
End of exclusive
*
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.
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.
x
#Data set
1: DT1
(12H)
This message corresponds to the actual data transfer process.
Because every byte in the data is assigned a unique address,
а
DT!
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 "soft-through"
mechanism.
To maintain
compatibility
with such devices, Roland
has
limited the DT1
to 256 bytes so that an excessively long
message
is sent out in separate segments.
Roland Exclusive Messages
Exclusive
Manufacturer
ID (Roland)
Device ID
Model
ID
Command
ID
Address
MSB
Data
ç Н
Check sum
End of exclusive
*
A DTI
message
is capable of providing only the valid
data among
those
specified
by an КО!
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.
s Example of Message
Transactions
@ Device
A sending
data to Device
B
Transfer of a DT]
message
is all thal takes place.
[Data
set
11
-------------ы-
* More
than
20m
sec
time internal.
[Data set 1]
-------------»-
[Data set
11
-------------»-
@ Device B requesting data from Device
A
Device
B sends
an
КО!
message
to Device
A.
Checking
the
message,
Device
A
sends
a
DTI
message
back
to Device
B.
Device (B)
[Data
set
1] -4————————
TN equest data]
[Data set 11
--------------»-
* More
than
20m
sec
time internal.
[Data set 11
-----------»-
{Data
set
11
———————————»-
31
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