Decoder outputs vs inputs: For a binary decoder, does having 2 select inputs imply only 2 outputs for the decoded value, or should it produce 2^n outputs?

Introduction / Context:
Decoders are one-hot generators: they convert an n-bit binary input into one of 2^n active outputs. They are used for address decoding, memory selection, and instruction demultiplexing. The stem claims a 2-input decoder has only 2 outputs; we will verify the general n-to-2^n rule and correct this misconception.

Given Data / Assumptions:

• Ideal binary decoder with n input (select) lines.
• Exactly one output is asserted for each input code when enabled.
• Active-high outputs assumed (active-low variants behave analogously).

Concept / Approach:
The defining property is exponential fan-out: an n-to-2^n decoder. For n = 2, outputs = 2^2 = 4. Typical parts: 2-to-4, 3-to-8, 4-to-16 decoders. Therefore, the claim of “two outputs” is incorrect. Confusing decoders with demultiplexers or simple selectors can cause wiring mistakes in address maps and control logic.

Step-by-Step Solution:

Verification / Alternative check:
Look up a standard 74HC139/138 family: for n = 3, 3-to-8 outputs; for n = 2, 2-to-4 outputs. Datasheets reaffirm the 2^n relation.

Why Other Options Are Wrong:
Enable polarity, Gray coding, or encoder terminology do not change the fundamental output count. “Correct” contradicts the definition.

Common Pitfalls:
Mixing up decoder (n→2^n) with demultiplexer (routes one input to 1 of 2^n outputs but still has 2^n outputs). Ensure device roles and counts are clear before schematic capture.

Final Answer:
Incorrect