Logic level conventions: In a positive-logic system, which electrical level represents logic 1 (HIGH)?

Introduction / Context:
Digital logic conventions define how electrical levels map to logical values. The most common convention is positive logic, where a higher voltage corresponds to logic 1 (HIGH) and a lower voltage corresponds to logic 0 (LOW). Clarity on this convention is vital when interfacing components and interpreting datasheets.

Given Data / Assumptions:

• Assume a positive-logic system (e.g., 0 V as LOW, VCC as HIGH).
• Voltage thresholds (VIH/VIL) define valid logic level ranges.
• Negative logic is the inverse mapping and is not assumed here.

Concept / Approach:
In positive logic, logic 1 corresponds to a higher voltage near the supply rail (e.g., 3.3 V or 5 V, subject to VIH), and logic 0 corresponds to a lower voltage near ground (below VIL). Designers select logic families with compatible thresholds to guarantee noise margins and reliable communication between devices.

Step-by-Step Solution:
Identify system type: positive logic → 1 is HIGH.Translate to electrical terms: HIGH = higher voltage level within specified VIH–VOH constraints.Choose “higher voltage level.”

Verification / Alternative check:
CMOS/TTL datasheets list VIH and VIL that align with this mapping; logic analyzers default to showing HIGH as a higher voltage trace.

Why Other Options Are Wrong:
Zero or lower voltage level indicate LOW in positive logic. Negative voltage is unrelated unless using special bipolar families or negative supplies with different conventions.

Common Pitfalls:
Mixing positive/negative logic conventions or forgetting that thresholds, not ideal rails, determine valid logic recognition.

Final Answer:
higher voltage level.