Combinational logic identification: Which combinational circuit generates a specific binary word (code) as its output corresponding to an active input line?

Introduction / Context:
Encoders and decoders are dual combinational circuits. An encoder accepts one-of-N active inputs and outputs the corresponding binary code (word). A decoder performs the inverse, taking a binary code and asserting one of several outputs. Understanding this distinction is critical in address decoding, keyboard scanning, and interrupt handling.

Given Data / Assumptions:

• We seek the circuit that outputs a binary word representing which input is active.
• Only one input is assumed active at a time in a basic encoder.
• Standard device roles: MUX selects inputs to a single line; DEMUX routes one input to many outputs.

Concept / Approach:
An n-to-2^n decoder takes an n-bit code and activates exactly one of 2^n outputs. Conversely, a 2^n-to-n encoder maps an asserted input line to its n-bit index code. Priority encoders extend this to handle multiple simultaneous requests by outputting the highest-priority index. Neither multiplexer nor demultiplexer inherently “generates” a binary word from a one-hot input set.

Step-by-Step Solution:
Identify the required behavior: produce a binary word from an active input line.Match that behavior to the encoder definition.Select “encoder.”

Verification / Alternative check:
Datasheets for 74HC147 (10-to-4 priority encoder) illustrate input lines mapped to 4-bit outputs.

Why Other Options Are Wrong:
Decoder generates one-of-N outputs given a code. Multiplexer selects among data inputs, not a code generator. Demultiplexer routes one input to multiple outputs.

Common Pitfalls:
Confusing the direction of data flow between encoders and decoders due to similar naming.

Final Answer:
encoder.