Standard TTL output behavior at logic HIGH For a standard TTL gate whose output is in the HIGH state, what is its guaranteed output-current capability and typical loading limit in terms of attached inputs?

Introduction / Context:
TTL (Transistor-Transistor Logic) families specify distinct source/sink capabilities depending on whether an output is HIGH or LOW. Designers must respect these limits to maintain valid logic levels and avoid overloading. The question focuses on the HIGH-state capability and the conventional fanout interpretation.

Given Data / Assumptions:

• Standard TTL input requirements: I_IH ≈ 40 µA (max), I_IL ≈ 1.6 mA (max).
• Standard TTL output capability: I_OH ≈ −0.4 mA (i.e., can source about 400 µA when HIGH), I_OL ≈ 16 mA (can sink when LOW).
• Fanout traditionally about 10 in both states for classic 74xx TTL.

Concept / Approach:
At logic HIGH, the TTL output can source only a small current (hundreds of microamps). Dividing the available source current by the required HIGH input current per load gives a loading limit of roughly 10 standard TTL inputs.

Step-by-Step Solution:

Verification / Alternative check:
Datasheets for 74xx TTL list these limits explicitly; TTL gates are stronger at sinking current in LOW state (16 mA) than sourcing at HIGH.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing source vs. sink directions; misapplying LOW-state numbers to the HIGH state; ignoring that different TTL subfamilies (LS, ALS, etc.) tweak values but preserve the general relationships.

Final Answer:
source 400 µA of current to no more than 10 attached gates