Flip-flop operating mode of optocoupler inputs
As you can see in the example stated below there is a changing input signal shown on by a optocoupler input.
The blue stripes mark the point of time when the states of the optocoupler inputs are asked PC sided.
The red marked change in voltage would not be noticed because the calling of optocoupler inputs is always a snap-shot.
Save change in state through flip-flops
By using flip-flops you can save a change in state on the module's inputs and you can recall it at the following PC sided access.
So you will not miss any short-thermed input signal changes.