Hi,
I want to connect an output from two separate Uno's to a stepper driver pulse input. I am worried that when Uno #1 applies the 5V signal that it may travel to the Uno #2 output pin and hurt it. The "End-in-Mind is that either Uno could move the stepper motor. Any advice would be appreciated. Thanks!
Don't make direct connections to the two outputs.
Use diodes to prevent one output fight the other.
Google "wired OR gate".
The resistor may be un-necessary.
Grady_Anderson:
Hi,I want to connect an output from two separate Uno's to a stepper driver pulse input. I am worried that when Uno #1 applies the 5V signal that it may travel to the Uno #2 output pin and hurt it. The "End-in-Mind is that either Uno could move the stepper motor. Any advice would be appreciated. Thanks!
Why two different UNO's?
What is the application?
Thanks.. Tom.. 
I'd send the step signal from Uno A to Uno B, so that B can merge the signals in a meaningful way before applying it to the stepper.