Roland D-50 - Page 109

*&The size of the requested data does not indicate the aumber
of bytes that will make up a DT1 message, bul represents
the address fields where the requested data resides.
%Some models are subject to limitations in data farmat used
for a single wansaction. 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,
# Data set 1: OT1 (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 data as well as 2 series of data formatted in an address
— dependent order.
The MIDE standards inhibit non-real time messages from
interrupting an exctusive one, This fact is inconvenient for the
devices that support a "soft-through” mechanism. To maintain
compatibility with such devices, Roland has limited the DT] we
256 bytes so that an excessively long message is sent out in
separate segments,
Byte Description
Exclusive
Manufacturer ID (Roland)
Device 1D
MOL Model ID
12H Command 1D
aaH Address MSB
° use
Check sum
End of exclusive
%*A DTI message is capable of providing only the valid data
among those specified by an RQi message,
Some models are subject to limitations in data format used
for a single transaction. Requested data, for example, may
have a fimit in length or must be divided into predetermined
address ficids 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,
# Example of Message Transactions
@Device A sending data to Device B
Transfer of a DT1 message is all that takes place.
[Data set 1) ————++_____»
%*More than 20m sec time internal.
{Data set 1)§ —————+_—_
(Data set 8} ———————__»
@ Device B requesting duta from Device A
Device B sends an RQE message to Device \. Checking tne
message, Device A sends a DTI message back to Device B.
{Dataset 1] —«—————{Reaves data}
{Gata set 1} ————_—_____»
%*More than 20m sec time internal.
(Data set 1) ————_——__
(Oata set 1) ————-—--__
4. | Handshake ~- Transfer Procedure
Handshaking is an interactive process where two devices
exchange error checking signals before a message (ransaction
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 it comes to handling large amounts of data- —sampler
waveforms and synthesizer tones over the catire range, for
example——across a MIDI interface, handshaking tcansfer is
more efficient than one-way transfer.
Want to send data WSD (40H)
Request data RQD (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 lo a device
at the other end of the interface, it contains data for the
address and size that specify designation and length,
respectively, of the data to be sent,
On receiving a WSD message, the remote device checks its
memory for the specified data address and size which will
satisfy the request. If it finds them and is ready for
communication, the device will retura an "Acknowledge
(ACK)” message.
Otherwise, it will return a "Rejection (RIC)" messaye.
Exclusive status
Manufacturer ID (Roland)
Device ID
Model ID
Command ID
Address MSB
use
MSB
tse
Check sum
End of exclusive
*The size of the data to be sent docs not indicale the number
of bytes that make up a “Data set (DAT)” message, but
represents the address fields where the data should reside,
%*Some models are subject to limitations in data format uscd
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—1D,
* The error checking process uses a checksum that provides
a bil pattern where the least significant 7 bits are zero when
values for an address, size, and (that checksum are summed.