Yamaha MOX8 Manual page 73

Stop (FCH)
Active Sensing (FEH) This is a type of MIDI message used to prevent unexpected results when
Timing Clock (F8H)
This message causes MIDI sequence data (song) to stop playing back.
This message will be transmitted when pressing the [ ] (Stop) button
during playback.
a MIDI cable is disconnected or damaged while the instrument is being
played.
Once this message has been received, if no MIDI data is subsequently
received within an interval period, the same function is performed as when
All Sounds Off, All Notes Off, and Reset All Controllers messages are
received, and the device returns to a status in which FEH is not monitored.
The interval period is approximately 300 msec.
This message is transmitted with a fixed interval (24 times per 1/4 note) to
synchronize connected MIDI instruments.
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MIDI