Design a Mealy sequential circuit which investigates an input sequence X and produces an

Chapter 16, Problem 16.9

(choose chapter or problem)

Design a Mealy sequential circuit which investigates an input sequence X and produces an output Z which is determined by two rules. The initial output from the circuit is Z = 0. Thereafter, the output Z will equal the preceding value of X (rule 1) until the input sequence 001 occurs. Starting with the next input after 001, the output Z will equal the complement of the present value of X (rule 2) until the sequence 100 occurs. Starting with the next input after 100, the circuit output is again determined by rule 1, etc. Note that overlapping 001 and 100 sequences may occur.

Example:

                   Rule: 1   1   1   1   2   2   2   2   2   1   1   2

                        X = 1   0   0   1   1   0   1   0   0   0   1   1

                        Z = 0   1   0   0   0   1   0   1   1   0   0   0

Design your circuit using NAND gates, NOR gates, and three D flip-flops. Your circuit should be provided with a method for manually resetting the flip-flops to the start state. A minimum solution requires six states. Any solution which is minimal for your state assignment and uses 12 or fewer gates and inverters is acceptable. (Assign 000 to the start state.)

Test Procedure: First, check out your state table by starting in each state and making sure that the present output and next state are correct for each input. Then, starting in the reset state, determine the output sequence for each of the following input sequences:

(1) X = 1    0   0   1   0   0   1   0   0   0   1   1

(2) X = 0   1   1   0   0   0   0   1   1   0   1   1