Roland TR-626 Owner's Manual page 90

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Request data : RQD (41 H)
This message is sent out when there is a need to acquire data
from a device at the other end of the interface. It contains data
for the address and size that specify designation and length,
respectively, of data required.
On receiving an RQD message, the remote device checks its
memory for the data address and size which satisfy the request.
If it finds them and is ready for communication, the device will
transmit a "Data set (DAT)" message, which contains the
requested data. Otherwise, it will return a "Rejection (RJC)"
message.
Byte
Description
F0H
Exclusive status
41H Manufactures
ID (Roland)
DEV Device ID
MDL
Model ID
41H
Command
ID
aaH Address MSB
LSB
ssH Size MSB
LSB
sum Check sum
F7H End of exclusive
* The size of the requested data does not indicate the number
of bytes that make up a "Data set (DAT)" 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 least significant 7 bits are zero when
values for an address, size, and that checksum are summed.
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Data set : DAT (42H)
110
This message corresponds to the actual data transfer process.
Because every byte in the data is assigned a unique address,
the message can convey the starting address of one or more
data as well as a series of data formatted in an
address-dependent order.
Although the MIDI standards inhibit non- real time messages
from interrupting an exclusive one, some devices support a "
soft- through" mechanism for such interrupts. To
maintaincompatibility with such devices, Roland has limited the
DAT to 256bytes so that an excessively long message is sent
out in separate segtnents.
Byte Description
F0H Exclusive status
41H Manufactures ID (Roland)
DEV Device ID
MDL Model ID
42H
Command
ID
aaH
Address MSB
LSB
ddH Data
:
sum Check sum
F7H End of exclusive
*A DAT message is capable of providing only the valid data
among those specified by an RQD or WSD 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.
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Acknowledge : ACK (43H)
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End of data
This message is sent out when. no error was detected on
reception of a WSD, DAT, "End of data (EOD)", or some other
message and a requested setup or action is complete. Unless
it receives an ACK message, the device at the other end will
not proceed to the next operation.
Byte Description
F0H Exclusive status
41H Manufactures ID (Roland)
DEV Device ID
MDL Model ID
43H Command ID
F7H End of exclusive
EOD (45H)
This message is sent out to inform a remote device of the end
of a
message. Communication, however, will not come to an
end unless the remote device returns an ACK message even
though an EOD message was transmitted.
Byte Description
F0H Exclusive status
41H Manufactures ID (Roland)
DEV
Device ID
MDL Model ID
45H
Command
ID
F7H End of exclusive
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Communications error : ERR (4EH)
This message warns the remote device of a communications
fault encountered during message transmission due, for
example, to a checksum error. An ERR message may be
replaced with a "Rejection (RJC)" one, which terminates the
current message transaction in midstream.
When it receives an ERR message, the sending device may
either attempt to send out the last message a second time or
terminate communication by sending out an RJC message.
Byte Description
F0H Exclusive status
41H Ma':'ufactures
ID (Roland)
DEV Device ID
MDL Model ID
4EH Command ID
F7H End of exclusive