Comparative Study on the Forbidden States of the SR Flip-flops

Abstract

In the teaching process of “Digital Electronic Technology†or “Digital Circuit†in colleges and universities, it is usually necessary to teach the forbidden states of the two “basic SR latchesâ€, the “synchronous SR flip-flopsâ€, the “master-slave SR flip-flop†and the “standard SR flip-flop†that do not satisfy the constraint condition. However, it is found in the examination of various teaching materials, many teachers have a vague understanding of the corresponding forbidden state, thus giving the wrong way of speaking. This paper gives a comparative analysis of various forbidden states, trying to clarify the ambiguity about them. Further, four new names of “both 0 state (or third state)†and “both 1 state (or fourth state)†are suggested, and suggestions for the correct truth table of the corresponding forbidden state in various situations are given. This paper is expected to play a positive role in the teaching of the electronic technology basic courses and in the preparation, re-preparation and publication of teaching materials.