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MIDI Implementation

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.’

•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.

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 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

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)

Device (B)Device (A)

Data Set 1

* Wait for 20 msec or longer.

Data Set 1

Device (B)Device (A)

Data Set 1 Request Data

Data Set 1

* Wait for 20 msec or longer.

Data Set 1

1 2 ... 56 57 58 59 60 61 62 63 64 65 66 ... 71 72

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