Standard supply for TTL logic Transistor–transistor logic (TTL) devices are designed to operate from what nominal supply voltage?

Introduction / Context:
Supply compatibility is crucial when mixing logic families. TTL has long served as a baseline for digital interfacing, with many systems designed around its nominal supply.

Given Data / Assumptions:

• Logic family: TTL (e.g., 74xx standard TTL).
• We refer to classic, not low-voltage CMOS derivatives.

Concept / Approach:
Traditional TTL operates at a nominal VCC of 5 V, with defined noise margins and input thresholds around this level. Many modern interfaces still accommodate 5 V logic or provide level shifting for compatibility.

Step-by-Step Solution:
Identify family: TTL.Recall nominal supply: VCC ≈ 5 V.Therefore, the correct supply is 5-volt.

Verification / Alternative check:
Datasheets for 74LS, 74ALS, and standard 74 series specify VCC = 5 V ± tolerance.

Why Other Options Are Wrong:
3 V: typical of some CMOS families (e.g., 3.3 V), not classic TTL.9 V and 12 V: used for analog subsystems or legacy logic families, not standard TTL.

Common Pitfalls:
Assuming all “74-series” are 5 V; 74HC/74HCT CMOS variants have wider ranges, and low-voltage families may run at 3.3 V—check the specific part.

Final Answer:
5-volt supply