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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, a DT1
message can convey the starting address of one or more bits of 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 devices that support a
"soft-thru" function.
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.'
Byte
Description
F0H
System Exclusive Status
41H
Manufacturer ID (Roland)
DEV
Device ID
MDL
Model ID
12H
Command ID
aaH
Address MSB
:
:
:
:
Address LSB
ddH
Data MSB
:
:
:
:
Data LSB
sum
Check sum
F7H
EOX (End of System Exclusive)
• A DT1 message is capable of providing only the valid data
among those specified by an RQ1 message.
• Some models are subject to limitations in data format used for a
single transaction. Requested data, or 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 last 7 bits are zero when values for an
address, data, and that checksum are summed.
Equipement MIDI (en anglais)
Example of Message Transactions
• Device A sending data to Device B
Transfer of a DT1 message is all that takes place.
fig.MessageTransaction1.eps
Device (A)
Data Set 1
* Wait for 20 msec or longer.
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 DT1 message back to
Device
fig.MessageTransaction2.eps
Device (A)
Data Set 1
Data Set 1
* Wait for 20 msec or longer.
Data Set 1
Data Set 1
Device (B)
Device (B)
Request Data
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