Previous Signal Memory Cell

A circuit that detects when its input changes and keeps a record of the signal type it was receiving before the input changed. Basically you have input > check > output, if the input changes the circuit detects a difference between the input and check, triggers the output to copy the check, then triggers the check to copy the input. For some reason in this game circuit behavior can sometimes change depending on the order that parts were placed, so if it isn't working right just delete and replace one of the wires around the second signal gate and it should be fine after that, if you've got a bunch of these in sequence then you might need to do this update to each link in the chain in order from the end of the chain to the start.