Tri-state (three-state) logic outputs: Which of the following is not a valid output state?

Introduction / Context:Three-state (tri-state) outputs allow a pin to be driven HIGH, driven LOW, or placed in a high-impedance (Hi-Z) state, effectively disconnecting it from the bus. Understanding these states is essential for bus sharing and multiplexed interfaces.

Given Data / Assumptions:

• Valid states: logic HIGH, logic LOW, and High-impedance (Hi-Z).
• Hi-Z allows multiple devices to share a line by de-asserting their drivers.
• “Low-Z” is not a distinct logic state; it describes impedance magnitude, not logic function.

Concept / Approach:The hallmark of tri-state outputs is the third state: High-Z. This state makes the output behave like an open circuit, enabling wired bus architectures. Any term that implies simply “low impedance” is not a defined tri-state mode, because both driven HIGH and driven LOW are low-impedance drive states by design.

Step-by-Step Solution:List tri-state modes: HIGH, LOW, High-Z.Evaluate each option.Identify “Low-Z” as not a logical state but a characteristic of active drive.

Verification / Alternative check:Datasheets describe output enable/disable controls resulting in Hi-Z when disabled; no device lists “Low-Z” as a third state.

Why Other Options Are Wrong:HIGH and LOW are driven states with low output impedance.High-Z is the legitimate disconnected state.“Hi-Z with weak pull” is still conceptually a High-Z state plus biasing, not a fourth state.

Common Pitfalls:Confusing impedance descriptors with logic states; only three logical output states exist in tri-state logic.

Final Answer:Low-Z