the midi looper changes between both signal chains. a midi controler sends the information to the midi-switcher to change between loop 1 and loop 2. see this page also: http://www.glab.com.pl/midi_2xloop_en
Finally got the expression pedal to work (I set the wrong expression pedal the cameleon's midi channel).
@Lazzari: I know a page written in german. But try wikipedia they should have some info about it.