Correct - On your SD90, Touch Menu then touch MIDI. At the bottom of the screen, you will see "Clock In" and "Clock Out". They will both be blue in color. If you touch either one they will change to a yellow background indicating they are "on" or "active".

Clock In = The SD90 is waiting for some other MIDI device to send stop/start/tempo information.

Clock Out = The SD90 will send that info to other MIDI devices you have in your setup AND are configured to accept that info.