A clocked sequential circuit is to be designed (using D flip-flops) that goes…
2022
A clocked sequential circuit is to be designed (using D flip-flops) that goes through sequence of repeated binary states 00, 01, 10, and 11 when value of external input x = 1. The state of the circuit remains unchanged when x = 0. Which statement is correct about the design of this circuit?
- A.
It requires 3 flip-flops.
- B.
It has one external output.
- C.
The input of the left-most flip flop (corresponding to most significant bit of the state) does not depend on external input x.
- D.
The input of the right-most flip flop (corresponding to least significant bit of the state) depends on external input x.
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Correct answer: D
This circuit functions as a 2-bit synchronous counter controlled by input x. When x=1, the state advances through 00 to 11; when x=0, it holds. The least significant bit toggles every clock cycle if counting is enabled, requiring D_LSB = Q_LSB XOR x. This dependency on input x distinguishes the correct design choice.