Digital logic levels (generic TTL-like): Which range is typically considered an INVALID region for a binary signal, i.e., neither a guaranteed LOW nor a guaranteed HIGH?

Introduction / Context:
Digital logic families specify valid input voltage thresholds to ensure robust interpretation of LOW and HIGH. The zone between these thresholds is the undefined or invalid region where reliable operation is not guaranteed.

Given Data / Assumptions:

• Assume TTL-like thresholds: VIL(max) ≈ 0.8 V and VIH(min) ≈ 2.0 V at a 5 V supply.
• Any voltage below VIL(max) is a valid LOW; any above VIH(min) is a valid HIGH.
• Between those limits is not guaranteed.

Concept / Approach:
Define valid regions and identify the gap. The invalid region is the interval between the maximum recognized LOW and the minimum recognized HIGH.

Step-by-Step Solution:
VIL(max) = 0.8 V.VIH(min) = 2.0 V.Invalid region = 0.8–2.0 V.

Verification / Alternative check:
Compare with CMOS at 5 V (typical higher margins), but the most commonly taught TTL thresholds set the classic undefined zone at about 0.8–2.0 V.

Why Other Options Are Wrong:
0.7–2.8 V: overbroad and does not match standard TTL specs.0.8–3 V or 0.7–2.5 V: do not reflect standard guaranteed thresholds.0–5 V: entire supply span, not an invalid region.

Common Pitfalls:
Assuming the midpoint (around 2.5 V) is valid. Unless specified by a particular logic family, it is in the no-man's-land for TTL.

Final Answer:
0.8–2 volts