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Standard flow table methods for analysis and synthesis of asynchronous sequential switching networks are difficult to apply when edge-sensitive flip-flops are used. Use of a differential mode (DM) state table, which specifies the next state as a function of the present state and input change, avoids such difficulties. Difference operators, which are used to specify changes in logic variables, provide a convenient means for defining terminal behavior of edge-sensitive flip-flops. The inhibited toggle flip-flop is introduced as a general-purpose edge-sensitive flip-flop. Sequential networks are analyzed by writing difference operator equations from which a DM table can be constructed. Synthesis of asynchronous networks is accomplished by first constructing a DM table to describe the desired network and then deriving input equations for inhibited-toggle flips-flops. Such realizations are free of hazards and critical races and usually require fewer gates and flip-flops than solutions by standard flow table methods.
Date of Publication: Aug. 1971