Paul, I reread your post and noted that you said only the up would work? You realize it is normally high 5v and drops to 0v for a pulse? Wouldn't only the down function work. Not trying to pick at you or anything, Im just really having a hard time grasping the interrupt concept and that confused me. If I am wrong in thinking the interrupts work on a sort of first come, first serve basis please explain. Also If i need to flip the pulse thats fine, the way I have it set up now just looks like a cleaner wave in my oscilloscope.