Question

In a synchronous sequential circuit, which of the following conditions may cause a race condition?

• A. If only combinational logic is used
• B. If asynchronous inputs are avoided
• C. If two or more state variables change simultaneously
• D. If the circuit has a single clock source

Hint:

A race appears when more than one state bit must flip at the same time and delays differ.

Answer 1

The Correct Option is C

Step 1: A race condition happens when the final state of a circuit depends on the exact order or timing in which signals change, rather than on the logic alone.

Step 2: In a sequential circuit the state is held by several state variables (flip-flop outputs). When a transition requires two or more of these state variables to change at the same time, tiny differences in gate and wire delays let one variable change slightly before another.

Step 3: Because the variables do not switch at exactly the same instant, the circuit may briefly pass through an unintended state and can settle in the wrong final state. This unpredictable behaviour is the race condition.

Step 4: Reviewing the options: using only combinational logic, avoiding asynchronous inputs, and having a single clock source all tend to reduce timing problems. The one condition that creates a race is two or more state variables changing simultaneously, so option (C) is correct.