# Logic Design Questions and Answers – Clocked Sequential Circuits – State Tables and Graphs

This set of Logic Design Multiple Choice Questions & Answers (MCQs) focuses on “Clocked Sequential Circuits – State Tables and Graphs”.

1. In the state diagram of any Finite State Machine, what does the symbol a/b signifies?

a) a and b both are input
b) a and b both are output
c) a is input and b is output
d) a is output and b is input

Explanation: Finite state machines are mathematical models those can be in only one of a finite number of states in a given time instant. According to standard rules, here a is the input to the state machine and b is the output for that input. Hence, the correct option is “a is input and b is output”.

2. What step is taken if there are two or more equivalent states in the state machine of any Finite State Machine?
a) All of them are kept as they are
b) Only one row of such state is kept and others are omitted
c) All of them are omitted
d) Any one row of the equivalent states are omitted

Explanation: Equivalent states are always used to minimize and simplify the state table. Then obviously they will not be kept as they are. So only one row of such state is kept and others are omitted. Keeping any of them unchanged does not lead to a good way to minimize state tables. That’s why keeping any one of the equivalent states, the others can be omitted.

3. Which of the following is the state equation for D flip-flop?
a) Q+ = D
b) Q+ = T ⊕ Q
c) Q+ = JQ’ + K’Q
d) Q+ = S + R’Q

Explanation: We know that D flip-flop is termed as a Data flip-flop because we get the exact same data that is present at the input. So if we take Q+ as the output and D as the input, we have to just equate the input and output to get the state equation, that is Q+ = D.

4. The given state graph is for a sequence detector circuit. Which sequence does is detect?

a) 1100
b) 1111
c) 0001
d) 1011

Explanation: To get the sequence, we have to follow all the next state transitions and ignore the paths where no next state transition occurs. And for the last state, we have to select the path for which a logic 1 output occurs. Thus, we get the transitions. Here the representation goes as (Present State, Input) ⟶ (Next State, Output)
(A, 1) ⟶ (B, 0)
(B, 0) ⟶ (C, 0)
(C, 1) ⟶ (D, 0)
(D, 1) ⟶ (A, 1)
Thus, we see that the input sequence 1011 makes all the transitions and gives the final; output 0. Hence, the correct sequence is 1011.

5. The state graph shown in the diagram is of which type of circuit?

a) Moore Machine
b) Mealy Machine
c) Type D circuit
d) Type E circuit

Explanation: The state transitions of the graph contains figures like a/b where a indicates corresponding input and b represents corresponding output. It indicates that the output of any state depends on the input value as well as the present state of the flip-flops. That is the main characteristic of a Mealy Machine.

6. What is the name of the element of a state diagram which uses right corner boxes to represent the state of any object?
a) Transitions
b) States
c) Iteration maker
d) Input

Explanation: State diagrams are pictorial representations of various state transitions taking place in any finite state machine. The state of any flip flop is displayed inside a right corner box or a circle in any state diagram. Hence, the right answer is states.

7. How many elements are there in a state diagram of any Algorithmic State Machine?
a) 1
b) 2
c) 3
d) 4

Explanation: The state diagrams of any Algorithmic State Machine are composed of 3 main elements. They are: i) State box, where the state of any element is represented. ii) Decision box, which has a condition true exit line and a condition false exit line, and iii) Conditional Output box, which is the final component of any ASM chart.

8. Which of the following is not present in the state table?
a) Input
b) Present state
c) Output
d) Previous state

Explanation: In a state diagram, the various state transitions of a finite state machine are pictorially represented. The state table consists of input, output, present state and next state. There is no need to put the previous state. Hence the correct answer is Previous state.

9. What is the shape of a conditional box in any Algorithmic State Machine?
a) Circle
b) Oval
c) Square
d) Rhombus

Explanation: Algorithmic state machines are methods for designing finite state machines. The box to represent any conditional operation in any Algorithmic State Machine chart is defined as an oval shaped block. Any condition mentioned in the algorithm may be mentioned inside this oval.

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