54XX vs. 74XX TTL logic series — what is the key difference? Compare the 54XX series of TTL logic gates with the 74XX series: which statement best describes the 54XX series?

Introduction / Context:
Classic TTL logic families were produced in two numbering schemes: 54XX and 74XX. Engineers often encounter both in mixed military/industrial contexts. Understanding the difference prevents misuse of parts outside their intended operating ranges and ensures reliability in harsh environments.

Given Data / Assumptions:

• 54XX parts are generally the military/extended-temperature versions.
• 74XX parts are commercial/industrial temperature range parts.
• Speed grades depend on subfamily (S, LS, ALS, etc.), not just the 54/74 prefix.

Concept / Approach:
The 54XX series typically supports a wider supply tolerance and an expanded operating temperature range (for example, –55 °C to +125 °C). The 74XX series commonly targets 0 °C to +70 °C or –40 °C to +85 °C, depending on subfamily and vendor. The electrical performance is otherwise similar for a given subfamily; the chief difference lies in environmental ratings and qualification standards.

Step-by-Step Reasoning:

Verification / Alternative check:
Vendor datasheets show identical logic functions and similar delays for 54LSxx vs 74LSxx, differing primarily in guaranteed limits over a wider temperature and voltage range for 54LSxx.

Why Other Options Are Wrong:

• “Faster/slower”: speed is subfamily-dependent (e.g., S vs LS), not dictated by 54 vs 74.
• “Narrower range”: opposite of the 54XX intent.
• “54XX uses CMOS”: both families are bipolar TTL in their classic forms.

Common Pitfalls:

• Assuming 54XX always has tighter timing—specs must still be checked by subfamily.

Final Answer:
54XX has a wider power supply and expanded temperature range.