This set of VHDL Multiple Choice Questions & Answers (MCQs) focuses on “Designing Moore Type FSM with VHDL”.
1. Output values of Moore type FSM are determined by its ________
a) Input values
b) Output values
c) Clock input
d) Current state
View Answer
Explanation: The output values of a Moore type FSM are determined only by its current state. The output is computed by the state outputs which serve as the input in the flip-flop. The output changes synchronously with the clock edge and state transition.
2. Moore machine output is synchronous.
a) True
b) False
View Answer
Explanation: Output of the Moore type FSM are synchronous, it works with respect to the clock and change only with the state transition. Mealy type FSM gives asynchronous output.
3. Finite state machines are combinational logic systems.
a) True
b) False
View Answer
Explanation: Finite state machines are SEQUENTIAL logic systems. In sequential logic systems, the output depends on the inputs and also on the present state of the system. It consists of a set of states, set of rules for moving from state to state, inputs and outputs.
4. What happens if the input is high in FSM?
a) Change of state
b) No transition in state
c) Remains in a single state
d) Invalid state
View Answer
Explanation: The system changes the state as long the input is high. The system also has an output which is 1 if the input is high since there is a change in state which leads to the output.
5. What happens if the input is low in FSM?
a) Change of state
b) No transition in state
c) Remains in a single state
d) Invalid state
View Answer
Explanation: There is no transition in the state if the input is low. If the system is in a particular state, it remains in that state only until the input becomes high. The system also has an output which is 0 if the input is low since there is no change in the state, it doesn’t reach the output state.
6. In FSM diagram what does circle represent?
a) Change of state
b) State
c) Output value
d) Initial state
View Answer
Explanation: In FSM diagram circle represent the states. For example: Assume there are four states in an FSM i.e. A, B, C and D. The encircled one out of the four will represent the state. If B is encircled, it shows FSM is in state B.
7. In the FSM diagram, what does arrow between the circles represent?
a) Change of state
b) State
c) Output value
d) Initial state
View Answer
Explanation: In the FSM diagram, arrows between the circles represent the change of one state to another state. For example: Assume there are four states in an FSM i.e. A, B, C and D. The arrow between the states A and B show the transition of state from A to B.
8. In the FSM diagram, what does the information below the line in the circle represent?
a) Change of state
b) State
c) Output value
d) Initial state
View Answer
Explanation: In the FSM diagram the information below the line in the circle represents the output value when in each state. It is represented by 1 and 0. If there is a state change then 1, otherwise 0.
9. Moore machine has _________ states than a mealy machine.
a) Fewer
b) More
c) Equal
d) Negligible
View Answer
Explanation: In Moore type FSM, more logic is required to decipher the outputs which result in more circuit delays. Moore machines generally respond one clock cycle later while mealy machines respond in the same clock cycle. That is why Moore machines require more states.
10. State transition happens _______ in every clock cycle.
a) Once
b) Twice
c) Thrice
d) Four times
View Answer
Explanation: Every arrow shows a transition from one state to another, transition of state happens once in one clock cycle. Depending on the present input, it may go to a different state every time so there is a change of state only one time.
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