In SR latch when apply a pulse to reset latch how the Q is changed?

Question

Here is the initial state of SR latch both reset and set inputs are zero.

Here we apply a pulse to the reset input and it shows it changes in this way first -

and then -

The thing that I don't understand how R pulse can change Q state without receiving feedback signal from second NOR gate, and second NOR gate must receive feedback signal from first NOR gate which one of them happens first?

Answer 1

The truth table of a NOR gate tells you that the output will only be 1, if both inputs are 0. As soon as one input gets to logic 1, the output switches to a logic 0.

When R is set to 1, the condition of both inputs being zero is no longer fulfilled -> The output goes immediately low to 0. At this time the lower NOR gate still has to wait for the logic 0 to appear at its upper input - until than it will stay low. But as soon as the higher input sees the 0 from Q, the gate has two low 0 as input and will switch the output to 1.