The Reactable supports the following MIDI protocols:
MIDI realtime sync: as master and as slave
MIDI notes/pitchbend: with the MIDI in object.
In order to use it as master, you have to click the Settings button and go to the MIDI tab. As soon as you enable the "master" toggle it will send MIDI timecode through your MIDI device. You should be able to see it on the device if it has a MIDI traffic indicator.
To use the Reactable in slave mode, tick the "allow slave" toggle button (disable the "master" if you do not want to daisy chain the sync signal). With "allow slave" mode on, the Reactable will lock into any MIDI sync coming from the selected MIDI in device. There is no "stop" messages, which means that if the sync stops the software will be freewheeling at the last bpm selected. With every MIDI start message it will hook into sync again.