I dislike asking questions - usually it means I didn't RTFM or that my Google skills are sub-par. Or that I'm missing the obvious. But here we are. The following advenure takes place on a Picaxe 28x1 project board (that came with the Solarbotics "Start Here" kit) with a resistor pack replacing the Darlington chip. The Parallax unit is connected to digital i/o pin 3 (though I see the same behavior on other pins). Output pin 2 is connected to an LED (but the same behavior holds for pins 4-7 which drive the motor outputs).
Here is some code: