Roland GR-30 Manual page 89

* The size of the requested data does not indicate the number of bytes that
will make up a DT1 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 last 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 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 Exclusive Status
41H Manufacturer ID (Roland)
DEV Device ID
MDL Model ID
12H Command ID
aaH Address MSB
| |
| |
LSB
ddH Data MSB
| |
| |
LSB
sum Check sum
F7H End of 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, 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 last 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 DT1 message is all that takes place.
Device A
[Data set 1]
* More than 20m sec time interval.
[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 B.
Device A
[Data set 1]
* More than 20m sec time interval.
[Data set 1]
[Data set 1]
Device B
Device B
[Request data]
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