Synchronous vs. asynchronous events — identifying true statements Which of the following statements is true regarding synchronous and asynchronous events in digital systems?

Introduction / Context:
“Synchronous” implies timing with respect to a shared clock; “asynchronous” implies independence from a common timing reference. Distinguishing these categories is essential for designing safe interfaces and for analyzing metastability risks when crossing clock domains.

Given Data / Assumptions:

• Synchronous events are coordinated by a clock edge or phase.
• Asynchronous events are not guaranteed to align to a single clock.
• We use conventional positive-logic, edge-sensitive clocking assumptions.

Concept / Approach:

Synchronous events in one clock domain occur “together” in the sense of being referenced to the same edge, while asynchronous events can arrive at arbitrary times relative to that edge. Thus, stating that asynchronous events “do not occur at the same time” (i.e., are not clock-aligned) captures the correct essence better than the other options.

Step-by-Step Solution:

Verification / Alternative check:

Consider an external button (asynchronous) into a CPU clock domain; arrivals are not clock-aligned and need synchronization.

Why Other Options Are Wrong:

Asynchronous events are not clock-controlled.

Synchronous events inherently need a clock.

“Only asynchronous events need a control clock” is backwards.

Common Pitfalls:

Interpreting “do not occur at the same time” too literally; the intent is “not aligned to a common clock.” Always add synchronizers for asynchronous inputs.

Final Answer:

Asynchronous events do not occur at the same time.