Dave Smith Instruments SYNTHESIZERS

I'd like to use a squarewave pulse coming through the audio input to run my sequencer clock 
on my PEK.  According to the manual, I can use external input peak as a modulation source, 
and sequencer clock as a destination, but seq clock doesn't show up in the destination menu 
in the modulators section.  Is there somewhere else to set this at, or do I need to change any 
global parameters to enable this?   Any help would be appreciated.