For a standard TTL output to be recognized as a valid logic HIGH by another TTL input, the output voltage must be at least ________ under load.

Introduction / Context:
Interfacing TTL devices safely requires meeting input threshold requirements. The output HIGH voltage under load must exceed the receiving device’s V_IH(min) to ensure a reliable HIGH.

Given Data / Assumptions:

• Family: standard 5 V TTL (e.g., 74LS/74ALS classes).
• We seek the guaranteed minimum HIGH output voltage specification.

Concept / Approach:
Typical TTL thresholds: V_IH(min) ≈ 2.0 V; V_IL(max) ≈ 0.8 V. To guarantee that a driven input sees a HIGH, the driver’s V_OH(min) is specified at or above 2.4 V at a defined I_OH. Hence, 2.4 V is the standard minimum HIGH output voltage rating for compatibility.

Step-by-Step Solution:
Recall TTL thresholds: V_IH(min) 2.0 V → driver must exceed this.Datasheets specify V_OH(min) 2.4 V at rated source current.Therefore, the correct minimum HIGH level is 2.4 V.

Verification / Alternative check:
Examine any 74LSxx datasheet: V_OH(min) commonly 2.4 V at I_OH = –0.4 mA (example value).

Why Other Options Are Wrong:
2.0 V is the input HIGH threshold, not output guarantee. 0.8 V is the input LOW maximum. 5 V is the supply, not the minimum. 3.3 V is unrelated to 5 V TTL standards.

Common Pitfalls:
Confusing input thresholds with output guarantees; always compare V_OH(min) (driver) against V_IH(min) (receiver) to ensure margin.

Final Answer:
2.4 V