Évaluations - 3, GPA: 3.3
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Facilité d'utilisation
Because every byte in the data is assigned a unique address, a DTI message can convey the starting address of one or more 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 the devices that support a "soft-through” mechanism. To maintain compatibility with such devices, Roland has limited the DTI to 256 bytes so that an excessively long message is sent out in separate segments. Byte Description FOH Exclusive 41 H Manufactures ID (Roland) DEV Device ID MDL Model ID 12H Command ID aaH Address MSB LSB ddH Data sum Check sum F7H End of exclusive ♦ A DTI 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 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 DTI message is all that takes place. Device (A) Device (B) [Data set 1] - ♦ More than 20m sec time internal. [Data set 1] -:- [Data set 1] I Device (A) [Data set I ] [Data set 1] - ♦ More than 20m sec time internal [Data set 0 Device (B) -[Request data] [Data set 1] m Handshake Transfer Procedure Handshaking is an interactive piwess where two devices exchange error checking signals before a message transaction 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 devicc returns a ready signal. When it comes to handling large amounts of data- • sampler waveforms and synthesizer tones over the entire range, for example—across a MIDI interface, handshaking transfer is more efficient than one - way transfer. Types of Messages Message Command ID Want to send data WSD (40H) Request data RQD (41H) Data set DAT (42H) Acknowledge АСК (43H) End of data EOD (45H) Communication error ERR (4EH) Rejection RJC (4FH) # Want to send data : WSD (40H) This message is sent out when data must be sent to 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 il finds them and is ready for communication, the device will return an "Acknowledge (АСК)” message. Otherwise, it will return a "Rejection (RJC)" message. Byte Description FOH Exclusive status 41H Manufactures ID (Roland) DEV Device ID MDL Model ID 40H Command ID aaH Address MSB LSB ssH Size MSB LSB sum Chec-k sum F7H End of exclusive ©Device B requesting data from Dcvice A Device B sends an RQ1 message to Device A. Checking the message, Device A sends a DTI message back to Device B. ♦ The size of Ihe dala to be sent does not indicate the number of bytes that make up a "Data set (DAT)" message, but represents Ihe address fields where the dala should reside. ♦ Some models are subject to limitations in data format used for a single transaction. Requested dala, 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 Ihe Model-ID. ♦ The error checking process uses a checksum that provides a bil pattern where ihe least significant 7 bils are zero when values for an address, size, and that checksum are summed. 45 £ Request data : RQD <41H) This message is sent out when there is a need to acquire data from a dcvice al 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 FOH Exclusive status 41H Manufactures ID (Roland) DEV Device ID MDL Model ID 41 H 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 represent...