I assuming that you mean by "not terminated" you mean that you simply do not 
have a pull up or pull down resistor on the two lines. The parallel port 
outputs can typically sink 24 ma but can only source 2-3ma. You would want to 
add pull up resistors to +5 in order to improve the signal levels. Adding pull 
down resistors will only decrease the high voltage level of the signal into 
your stepping motor control. Use 470 ohm resistors and that should be fine. 
Depending on what your logic inputs are (TTL, CMOS, etc) to the stepping motor 
controls, you may be fighting a ground noise issue. That I couldn't address 
without knowing what the circuitry looked like.

best regards, Steve Thatcher

-----Original Message-----
>From: Steve Robertson <stee...@ccvn.com>
>Sent: Mar 28, 2010 10:06 AM
>To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
>Subject: [Emc-users] Breakout Board Problems
>
>Hey Guys,
>
>Been testing my machine and am having trouble with random movement of each
>of the axis. I believe the problem is because the input to my homemade
>driver boards is high impedance and the STEP and DIRECTION lines are not
>terminated. Any voltage spikes or EM interference in the immediate area,
>like the laminate trimmer that I'm using as a cutting tool, seems to cause
>the problem.
>
>To supress (hopefully) the problem, I figured I'd just put termination
>resistors on the breakout board. So... I'm guessing the value of the
>termination resistors would not be critical but, surely, there is a correct
>value. What would be the correct value for a resistor between the STEP /
>DIRECTION signals and Ground?
>
>I'll also add some decoupling caps to the Power Supply lines to stop any
>potential problems there.
>
>TIA, Steve Robertson
>steverob [at] ccvn [dot] com
>
>
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Try the new software tools for yourself. Speed compiling, find bugs
proactively, and fine-tune applications for parallel performance.
See why Intel Parallel Studio got high marks during beta.
http://p.sf.net/sfu/intel-sw-dev
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