#
Data set
1
The size of Ihe
requested
data does not indicate the
number
of bytes thai
will
make up a DTI message, btii
represents
the address fields where the requested dais
resides.
Same 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
thai provides
a
bit pattern
where the least significant
7
bits
are zero when
values for Bn
address, size, and that checksum
are summed.
DT1 (12H)
This me
ssage corresponds
to the actual data transfer
process.
Because 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 "soft -through"
mechanism.
To maintain
compatibility with such devices, Roland
has limited
the DTI to
2S6 bytes so that an excessively long message
is sent out in
separate segments.
Device (A)
Device (B)
Byte Description
FOH Exclusive
41H Manufacturer
ID (Roland)
DEV
Device ID
MDL Model ID
12H
Command ID
as H Address MSB
LSB
dc H Da a
SL m
Chf ck sum
F7H
End of
exclusive
*A DTI message is capable
of
providing
only
the
vaiid
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
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.
#
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]
[Data set 1]
«
[Data set
I] •»-
More
than 20m
sec time
internal,
[Data set
I] :
**•
-{Request data}
[Data
set
1]
Handshake-
Transfer
Procedure
Handshaking 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 between message
transactions,
handshake
transfer allows
much speedier transactions because
data transfer starts
once the receiving device
returns a ready
signal.
When it comes to handling large amounts
of data
—
sampler
waveforms and synthesizer
tones
over
the entire range, for
example- -across
a MIDI interface, handshaking
transfer is
more efficient lhan one-way
transfer.
Types of
Messages
Message Command ID
Want
to
send data
WSD
(40H)
Request data
ROD (4JH)
Data set
DAT (42M)
Acknowledge
ACK (43H)
End of data
EOD (45H)
Communication error
ERR (4EH)
Rejection RJC (4FH)
#
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
,
respectively,
of the
data
lo
be
senl.
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 device will
return an
"Acknowledge
(ACK)"
message.
Otherwise,
it will return a "Rejection
(RJC)" message.
Byte
Description
FOH Exclusive
status
41H
Manufacturer
ID (Roland)
DEV
Device
ID
MDL
Model ID
40H
Command ID
aaH Address MSB
LSB
SsH Size
MSB
LSB
sum
Check
sum
F7H End of
exclusive
•
Device
B requesting data
from
Device
A
Device
B sends an
RQJ message to Device
A. Checking the
message, Device
A
sends
a DTI message back
to Device
B.
The size of the data to
be sent does not indicate
the
number
of bytes that make up
a "Data set
(DAT)" message,
but
represents the address
fields where the
data should
reside.
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
inlo predetermined
address fields before it
is exchanged across
the
interface.
The same number
of byles 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 arc zero when
values
for an address,
size, and
that checksum arc summed.
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