DATA FORMAT

DATA TYPES

Status Bytes

Status bytes are eight-bit binary numbers in which the Most Significant Bit (MSB) is set (binary 1). Status bytes serve to identify the message type, that is, the purpose of the Data bytes which follow the Status byte.

Except for Real-Time messages, new Status bytes will always command the receiver to adopt their status, even if the new Status is received before the last message was completed.

Running Status

For Voice and Mode messages only, when a Status byte is received and processed, the receiver will remain in that status until a different Status byte is received. Therefore, if the same Status byte would be repeated, it may (optionally) be omitted so that only the correct number of Data bytes need be sent. Under Running Status, then, a complete message need only consist of specified Data bytes sent in the specified order.

 

The Running Status feature is especially useful for communicating long strings of Note On/Off messages, where "Note On with Velocity of 0" is used for Note Off. (A separate Note Off Status byte is also available.)

Running Status will be stopped when any other Status byte intervenes, except that Real-Time messges will only interrupt the Running Status temporarily.

Unimplemented Status

Any status bytes received for functions which the receiver has not implemented should be ignored, and subsequent data bytes ignored.

Undefined Status

Undefined Status bytes must not be used. Care should be taken to prevent illegal messages from being sent during power-up or power-down. If undefined Status bytes are received, they should be ignored, as should subsequent Data bytes.

Data Bytes

Following the Status byte, there are (except for Real-Time messages) one or two Data bytes which carry the content of the message. Data bytes are eight-bit binary numbers in which the MSB is reset (binary 0). The number and range of Data bytes which must follow each Status byte are specified in the tables which follow. For each Status byte the correct number of Data bytes must always be sent. Inside the receiver, action on the message should wait until all Data bytes required under the current status are received. Receivers should ignore Data bytes which have not been properly preceeded by a valid Status byte (with the exception of "Running Status," above).