GATE CS 2005 Q64 — Combinational Circuits

By analyzing the given sequential circuit, we identify the logic gates feeding the inputs of the two $D$ flip-flops:

• The input to the first flip-flop is $D_0 = \overline{Q_0 + Q_1}$ (NOR gate).
• The input to the second flip-flop is $D_1 = Q_0 \odot Q_1$ (XNOR gate).

Since the flip-flops are positive edge-triggered, the next state $Q_0^+ Q_1^+$ is determined by the current inputs $D_0 D_1$. We can trace the state transitions starting from the initial state $Q_0Q_1 = 00$:

Thus, the state transition sequence starting from $00$ is:

$$\text{00} \rightarrow \text{11} \rightarrow \text{01} \rightarrow \text{00} \rightarrow \dots$$

This corresponds to the sequence shown in Option D.