Several subsets of the general sequential circuit model Excitation Variables INPUT(t) Combinational Combinational Memory Transform CLK (S) OUTPUT(O) State variables Simple sequential counter model E=f(St S+1=f(S,E) O=gsySeveral Subsets of the general sequential circuit model Excitation Variables Memory M State Variables CLK (E) Combinational Transform (f) INPUT(t) （S） Combinational Logic （g） OUTPUT(O) Simple sequential counter model E=f(St ) St+1=f(St ,E) O=g(St )