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%* The size of ihe requested data does nol indicate the number
of bytes thal will make
up a fT]
message, bul represents
ihe address fields where
the requested daia resides.
*Same
models are subject
to limitations in data formal used
for a single transaction.
Requested
data,
for example, may
have a limit in tength ar must be divided into predetermined
address fields before it is exchanged across the interface.
*The same number of bytes comprises address and size dala,
which, however, vary with the Model~!D_
*The
error
checking
process
uses
a checksum
thal
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; DT1
(12H)
This message corresponds to the actual data transfer process,
Because every byte in the data js assigned a unique address,
a
DTl
message
can
convey
the
starting
address
of one
or
more date 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 ane, This fact is inconvenient for the
devices that support 8 "saft—through" mechanism. To maintain
compatibility with such devices, Roland has limited the DT]
to
256 bytes so that an excessively long message is sent out in
separale segments,
Description
Exclusive
4tH
Manufacturer iD (Roland)
DEV
Device
ID
MDL
Mode!
ID
12H
Command
ID
aH
Address MSB
Lse
dH
Data
sum
Check sum
End of exclusive
%*A DTI message is capable of providing only the valid dala
among
those specified by an RQ}
message.
%Some models are subject ta limitations in data format used
for a single transaction.
Requested data, for exampie, may
have a limit in length or must be divided into predetermined
address fields before it is exchanged
acruss the interface.
%*The number of bytes comprising address data varies from
one
Modet~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 io Device B
Transfer of a DT1
message
is afl that takes place.
(Data set 1)—§
———————_——_»
More than 20m sec time internal.
(Data set 1))§
—————_______»
(Data set 1))©§ —————______»
@ Device B requesting data from Device
A
Device B sends an RQ1
message
to Device A, Checking the
message, Device A sends a DT]
message
back to Device B.
[Data set 1} —e———----___---{lequest
data]
{Oata sat 1}
——
%More
than 20m sec time internal,
{Data set 1}
[Data set 1}
ep
le
Gi Handshake- Transfer Procadure
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
jl 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 than one—way transfer,
Want to send data
| WSD (40H)
Request
data
ROD (41H)
Data set
DAT (42H)
Acknowledge
ACK (43H)
End of data
EOD (45H)
Communication error | ERR (4EH)
Rejection
RUC (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 cantains data for the
address
and
size
that
specify
designation
and
length,
respectively, of the data lo be seni,
On
receiving
a WSD
message, the remote
device
checks
its
memory
for the specified data address and size which wilt
satisfy
the requesl,
If it finds
them
and
is ready
for
communication,
the device
will return
an
"Acknowledge
{ACK)"
message.
Otherwise, il will return a "Rejection
(RJC)"
message.
Byte
L Description
|
FOH
Exclusive
status
4tH
Manufacturer
ID (Roland)
DEV
Device ID
MDL
Madei ID
40H
Command
ID
Address
MSB
LSB
ssH
Size
MSB
,
Use
sum
Check
sum
FH
End of exclusive
* The size of the data ta be sent daes not indicate the number
of bytes that make up a "Data sel
(DAT)"
message, bul
represents the address fields where the dala should reside,
Some
models are subject 1o limitations in data
format
used
for a singie transaction,
Requested data, for example, may
have a limit in length or must be divided inlo predelermined
address
ficlds before it is exchanged
across
the
interface,
*The same number of byles camprises address and size data,
which, however, vary wilh the Mndet- 11>.
*The error checking process uses a checksum (hut provides
a bit pallern where the ieast significant 7 bits are zero when
valves for an address, size, and (hat checksum arc summed,
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