A MIDI event that carries the MIDI active sense message tells a MIDI device that the MIDI connection is still active.
This message belongs to the category of MIDI system realtime messages.
This message consists of a single byte of data. This byte is the status byte and has a value of 0xFE.
If there are no other messages being sent over the MIDI connection, this message ensures that the receiving MIDI device knows that the connection is still open. If there are no other messages, this message may be sent at a minimum once every 300 milliseconds.
Musical Instrument Digital Interface (MIDI)