74HC21 input count In the 74HC21 device, how many inputs does each logic gate have?

Introduction / Context:
Knowing the pin functions and gate configurations of standard logic ICs speeds up schematic reading and circuit design. The 74HC21 is a common CMOS member of the 74HC family used where multi-input AND functionality is required.

Given Data / Assumptions:

• 74HC21 = Dual 4-input AND gate (two gates per IC).
• Each gate has the same number of inputs.
• Standard 14- or 16-pin packaging conventions apply (family dependent).

Concept / Approach:

Datasheets list 74HC21 as “Dual 4-input AND gate.” Therefore, there are two independent AND gates inside the chip, and each gate has four inputs feeding a single output. This configuration is useful when many conditions must be simultaneously true to assert a control signal.

Step-by-Step Solution:

Verification / Alternative check:

Look up the functional diagram: pins are grouped into two sets of four inputs converging on two outputs, confirming the 4-input nature per gate.

Why Other Options Are Wrong:

• 1, 2, or 3 inputs do not match the part’s standard description.
• 8 inputs would suggest a single very-wide gate, not the dual 4-input configuration.

Common Pitfalls:

• Confusing 74HC21 (dual 4-input AND) with 74HC08 (quad 2-input AND) or 74HC11 (triple 3-input AND).

Final Answer:

4