TTL–CMOS pin and level compatibility: Evaluate — “The CMOS series that is pin-compatible with the TTL family is the 4000 series.”

Introduction / Context:
Interfacing TTL and CMOS requires attention to pinout and logic-level compatibility. Although the classic 4000-series CMOS offers wide supply ranges, its pinouts and threshold levels are not generally drop-in compatible with the 74xx TTL family. The 74HC/74HCT families were introduced to address this compatibility need.

Given Data / Assumptions:

• TTL family reference: 74xx numbering and pinouts.
• CMOS families: 4000 series (CD40xx), 74HC, 74HCT, etc.
• “Pin-compatible” typically implies identical functions, pinouts, and practical logic-level compatibility at 5 V.

Concept / Approach:
The 4000 series predated 74HC/HCT and uses different pinouts/functions for many parts. 74HC mirrors 74xx pinouts and functions (CMOS implementation), while 74HCT also aligns logic thresholds to be TTL-level compatible at 5 V. Hence, the statement that the 4000 series is the compatible series is incorrect.

Step-by-Step Solution:

Verification / Alternative check:
Part comparisons (e.g., 74HC00 vs. CD4011) show function similarity (NAND) but differing pinouts and electrical thresholds; 74HC00 matches 7400 pinout, confirming compatibility.

Why Other Options Are Wrong:

• Correct / partial exceptions: A few devices (e.g., 4049/4050 level shifters) do not make the whole 4000 series pin-compatible.
• Mechanical-only compatibility: Even mechanical pinout often differs; logic thresholds certainly do.

Common Pitfalls:
Assuming all CMOS families are interchangeable; ignoring TTL input threshold requirements; overlooking supply voltage differences.

Final Answer:
Incorrect