Pushing electrons the other way ?

[whitney]

I have been working on the electronics phase of my project (my weak area) and have a couple questions on how to make the stepper run opposite direction. (CW/CCW)

To start out I stripped back the wires in my LPT cable, did a continuity test to make sure I knew what was where and hooked in two meters on what I programed as my Y axis (Turbo CNC). I ran my test part to watch the output on the cable and was pleasantly surprised. I could see what appeared to be motion output on the step, and the direction lead. I observed .7mv to 45 mv on one meter and .7mv to 5v on the other. At times I would observe an open circuit.
Seems like things are working like they should, now I can build a controller
(http://pminmo.com/3axis/3axis.htm) .

Question:
What makes the motor switch direction on the axis? at no time did I see any change in polarity? It must be in the IC on the controller?

[pastera]

The phase or timing of the coil currents determines direction. On a bipolar drive the current does reverse, but the timining of the current on/off/reversal in the two coils controls direction.

Aaron