Basic logic behavior of an OR gate For a standard OR gate in digital electronics, under what input condition is the output LOW?

Introduction / Context:
OR gates are fundamental building blocks in digital logic. Understanding their truth tables is essential for analyzing combinational circuits, designing control logic, and debugging gate-level implementations in microcontrollers, FPGAs, and ASICs.

Given Data / Assumptions:

• A standard positive-logic OR gate is used.
• Logic HIGH represents a logical 1, and logic LOW represents a logical 0.
• No degraded or undefined logic levels are considered; ideal digital behavior is assumed.

Concept / Approach:

An OR gate outputs HIGH if at least one of its inputs is HIGH. Conversely, its output is LOW only when every input is LOW. This behavior is captured succinctly by the Boolean expression: Y = A + B + C + ... where + denotes the OR operation. If every input equals 0, then Y = 0; otherwise Y = 1.

Step-by-Step Solution:

Verification / Alternative check:

Constructing a truth table confirms that the only row producing a LOW output is the row where all inputs are LOW. Any single HIGH immediately makes the output HIGH, reflecting the inclusive nature of OR.

Why Other Options Are Wrong:

• Any input is LOW: an OR gate can still output HIGH if a different input is HIGH.
• Any input is HIGH: this actually makes the output HIGH, not LOW.
• All inputs are HIGH: also produces HIGH output.
• Alternating inputs: as long as at least one is HIGH, the output is HIGH.

Common Pitfalls:

• Confusing OR with AND. AND requires all inputs HIGH for HIGH output; OR requires only one.
• Mixing active-low logic. With bubbles (inversion), truth behavior flips; here we assume standard positive logic.

Final Answer:

all inputs are LOW