The test items have the ability to "recover" from a missed transition and keep on working. Therefore, I need to run through the entire test if I want to and then look back at the data. (There might be an unforeseen situation where I need to stop the test immediately, but that's not the plan.) The Existing Read Error LEDs light up if there was no high to low transition during the latest (for example) 10 second polling. The Previous Read Error LEDs are also turned on at this point. If on the next go around (in say 30 mins) I see transitions the Existing Read Error LEDs turn off, but the Previous Read Error LEDs will always stay on. It is just a quick visual indicator of how things are running and not necessarily a requirement to stop the test.
I don't know if that changes things, but I wanted to clarify further. I'm trying to create the right balance between giving too many unnecessary details and not explaining enough. Hopefully it's becoming clearer now.
I do like your suggestion though with the while loop and shift registers checking for a transition and will see if that does what I want. And if not for this particular situation, it may prove useful in the future.
