Interesting Xylotek stepper problem

[Ray Henry <rehenry-at-up.net>]

List

Recently I was playing with a Sherline minimill with those laser engraved 
handwheels right on the motors and found an interesting problem with the 
Xylotek stepper driver cards.

Steppermod causes a motor to move the direction it was going for one pulse 
after a direction change.  In the eternal scheme of things it will never be 
more than one step or microstep off and it always corrects itself after the 
next direction change.  It is just a bit disconcerting to watch the Sherline 
handwheel take a wrong step when you press the 0.0001 jog button. 

A recent post from Jeff Pollard, Xylotek's wizard says;

> If you look at PDF page 3 in my datasheet at:

> http://www.xylotex.com/XS35V.pdf

> you can see the timing diagram of how the STEP/DIR signals need to be.  The
> DIR line needs to be stable 200 ns BEFORE and AFTER the RISING edge of the
> STEP signal.

> Is is possible that you are using a FALLING edge to trigger the STEP
> signal.  This would most likely be the case if you were used to using
> Geckos that require a FALLING signal (which allows their optoisolator to
> fire).

Freqmod is fine with this.  Matt tells me that is because there is a one 
motion loop delay after a direction change.  

What are the possible fixes here?

Ray