The plus (+) indicates a more advanced problem and the asterisk (*) indicates that a solut...

The plus (+) indicates a more advanced problem and the asterisk (*) indicates that a solution is available on the Companion Website for the text.

+The sequence in Problem 1 is a flag used in a communication network that represents the beginning of a message. This flag must be unique. As a consequence, at most five 1s in sequence may appear anywhere else in the message. Since this is unrealistic for normal message content, a trick called zero insertion is used. The normal message, which can contain strings of 1slonger than 5, enters input X of a sequential zero-insertion circuit. The circuit has two outputs, Z and S. When a fifth 1 in sequence appears on X, a 0 is inserted in the stream of outputs appearing on Z and the output S = 1, indicating to the circuit supplying the zero-insertion circuit with inputs that it must stall and not apply a new input for one clock cycle. This is necessary because the insertion of 0s in the output sequence causes it to be longer than the input sequence without the stall. Zero insertion is illustrated by the following example sequences:

Sequence on X without any stalls: 01111100111111100001011110101

Sequence on X with stalls:0111111001111111100001011110101

Sequence on Z:0111110001111101100001011110101

Sequence on S:0000001000000010000000000000000

(a) Find the state diagram for the circuit.

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(b) Find the state table for the circuit and make a state assignment.

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(c) Find an implementation of the circuit using D flip-flops and logic gates.

Problem 1

Repeat Problem 2 for the sequence 01111110 that is used in a different communication network protocol.

Problem 2

A Universal Serial Bus (USB) communication link requires a circuit that produces the sequence 00000001. You are to design a synchronous sequential circuit that starts producing this sequence for input E = 1. Once these quence starts, it completes. If E = 1, during the last output in the sequence, the sequence repeats. Otherwise, if E = 0, the output remains constant at 1.

(a) Draw the Moore state diagram for the circuit.

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(b) Find the state table and make a state assignment.

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(c) Design the circuit using D flip-flopsand logic gates. A reset should be included to place the circuit in the appropriate initial state at whichE is examined to determine if the sequence of constant 1s is to be produced.