MIDI System Real-Time Messages

**MIDI System Real-Time Messages**
Status Byte	Data Bytes	Message	Description
F8	-	Timing Clock	MIDI clock. This message is used to sychronise timing across sequencers in a MIDI system. (note 1) `24 clocks =` 1 quarter note
F9	-	Undefined	The current Running Status is not affected.
FA	-	Start	Used to synchronise the start-up of sequencers The sequence must start from song position 0 Sequencing begins at song-position 0 when the next Timing Clock message is received (note 2) (note 3)
FB	-	Continue	Continue Used to tell a sequencer to continue playing the current song from where it last left off. The sequencer should continue from the current song-position when the next Timing Clock message is received (note 2) (note 3)
FC	-	Stop	Used to tell a sequencer to stop playing. Any subsequent MIDI Timing Clock messages are to be ignored. Note-off messages should be sent for all notes which are still on, and all controllers should be returned to their 'normal' settings. The current song position pointer should be stored, so that playing can continue from the same point if a MIDI Continue message is received. (note 3)
FD	-	Undefined	The current Running Status is not affected.
FE	-	Active Sensing	This signal may be sent by a MIDI transmitter when there is no other activity. (note 4) It is sent after every `300ms` (nominally) of inactivity. A MIDI transmitter should send this message after 270ms of inactivity, while a MIDI receiver should expect it within 330ms. Once this message is received, Active Sensing is 'on', and the receiver should perform an All-Notes-Off if there is no MIDI activity for more than 330ms. It is functionally similar to a 'carrier' signal for a modem - it indicates the 'line' is still operational.
FF	-	System Reset	System Reset. The system should be set to the following states: Omni on, Polyphonic Local control on All notes turned off All controllers returned to their 'normal' settings Any song playing stopped Song Position Pointer = 0 Running Status is cleared Reset to power-up conditions

Footnotes

Note 1: A MIDI Real Time message, in particular the MIDI Timing Clock message, may be inserted into the middle of another message, without affecting that message or cancelling the current Running Status.
Note 2: The requirement to wait for the next MIDI Timing Clock only applies if the sequencer is being synchronised from an external MIDI clock, rather than its own internal clock.
Note 3: Any superfluous Real Time messages should be ignored. For example, if a Start message is followed by a subsequent Start message, the second Start message should have no effect.
Note 4: There is no requirement for a MIDI device to support Active Sensing either as a transmitter or a receiver. It must be ignored by a receiver if it is not supported.

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