Electronics world

A basic Flip-Flop circuit can be constructed in two ways. • Using two NOR gates • Using two NAND gates We know that a flip-flop circuit consists of two inputs set(S) and reset(R), two outputs Q and Q’. A cross coupled connection is given between output of one gate and the input of the other gate. Such type of cross coupled connection constitutes the feedback path for the flip-flops. These flip-flops are called direct coupled RS Flip flops (or) SR latch. Now to analyze the circuit let us assume that the 1) SET input = 1 and RESET input = 0. For convenience let the Set input be S and Reset input be R. We know that if any input of NOR gate is 1 then its output is 0. Therefore when S=1, the output of the gate corresponding to S (Gate 2 in figure) becomes 0. So Q’ becomes 0. This Q’ is given as an input (Cross coupled connection) along with R to the other gate. So the output of the second gate, Q becomes 1(since both R and Q’ are 0). Conclusion 1: When S=1 and R=0. The outputs Q’=0 and Q=1. Now when the set input(S) returns to 0, the output remains the same. This is because the output of gate 1 (ie) Q is 1.Now the inputs to gate 2 are S=0 and Q=1. So from the truth table of NOR gate we can say that Q’=0.