This chip converts standard TTL step and direction signals to the phase signals used by a unipolar stepper motor for two axes.

  Source code for the U-2 (a PIC 16F84 running a dedicated program) can be downloaded here and you can program the IC's yourself.  If you don't have a PIC programmer or are feeling lazy, you can buy pre-programmed and tested chips from me for $10 apiece.  See the ordering page for details.

   Hakan Ertan has uploaded code that adds full/half-step selection on pin 3.  Download his code here.  He has also submitted code for a version that runs on the PIC12C508A microcontroller.

  Here is a sample circuit schematic using the U-2 as a stepper driver for two unipolar motors (click view full-size)

NOTE:  Don't fudge the value of the RC pair on the OSC1 pin.  It's setting the clock speed of the chip.  A 22 pF cap looks a chili bean with two wires stuck in it, and has an underlined 22 .

  The step pin needs to be held low for 20 clock cycles minimum in order to guarantee that the chip will read it in time.  For the 2.5 MHz clock speed in the circuit shown, this works out to about 32 uS.  For TurboCNC, I set the pulse width to 40 uS just to be safe.