Is there a straightforward way to have a state change on any one of several logic lines trigger a state change on a single pin?
Imagine, for example, that I have two quadrature encoders and want to connect them to an Arduino, which only has 2 external interrupts. (Even worse, my Ardumoto shield from Sparkfun uses one of those pins as a PWM output.) Anyway, it seems that I should be able to feed the pulses from all 4 lines to some sort of circuit which would then toggle its output when any of its inputs change. That way I only need one interrupt to call an ISR which then checks the state of four pins and calculates rotation. By the way, I may need the resolution provided by following all 4 transitions, so just interrupting on one of the quadrature lines might not do the trick.
It seems like the solution might be a cascade of flip flops. But I don't want to reinvent the wheel, as it were, if such a thing already exists. This can't be a novel concept, right?
I ran a few searches here and on the internet at large and did not find much. Perhaps I am using the wrong search terms.
Thanks for your help.