Handling unused TTL inputs safely: Evaluate the statement: “Unused TTL logic inputs should be tied LOW.”

Introduction / Context:
Proper termination of unused logic inputs prevents noise pickup, oscillation, and excess current. TTL and CMOS families have different input structures, so the best practice is family-dependent. This question checks safe handling for unused TTL inputs.

Given Data / Assumptions:

• Standard TTL input structure exhibits a default bias toward logic HIGH when left open (due to multi-emitter transistor input network).
• We want to avoid unnecessary current draw and erratic behavior.
• We are not discussing open inputs for CMOS, which must never be left floating.

Concept / Approach:
Unused TTL inputs are commonly tied HIGH, not LOW. Tying LOW often sinks current through the input transistor network, increasing power dissipation. If leaving open is acceptable per the datasheet for certain gates, tying HIGH (directly or via a pull-up) is still preferred for noise immunity. CMOS, by contrast, must never be left floating; it should be tied definitively to HIGH or LOW through a resistor, but that is a separate rule.

Step-by-Step Solution:

Verification / Alternative check:
Classic TTL datasheets and application notes recommend tying unused inputs to VCC (often via a resistor) or connecting them to another driven input to ensure a defined HIGH.

Why Other Options Are Wrong:

Common Pitfalls:
Applying CMOS rules to TTL; assuming all logic inputs behave the same when left floating.

Final Answer:
Incorrect