[kamocat]

Does the semi-period mode in the counters actually measure period (that is, measuring between the ON edges of a digital signal), or does it measure pulse length (measuring the time the signal is OFF)?

I was about to wire up the trigger for some maxbotix SONAR when I realized that perhaps I could wire the entire thing to the digital sidecar, not the analog inputs. (That way there would be less noise, and there wouldn't be the problem with sudden changes in distance).