HDL description of a demultiplexer (DEMUX): In hardware description languages (e.g., VHDL/Verilog), which construct best and most exactly describes DEMUX behavior (one input routed to one of many outputs under select control)?

Introduction / Context:
A demultiplexer (DEMUX) routes a single input to one of several outputs based on select lines. In HDL, we need a construct that cleanly expresses conditional, signal-level behavior that can infer combinational logic during synthesis and is easy to simulate.

Given Data / Assumptions:

• Target: combinational DEMUX behavior.
• HDL choices include concurrent assignments, processes with if/case, and functions.
• Goal: single-source, multiple-destination routing under select.

Concept / Approach:
In VHDL, a process containing a case or if-elsif chain on the select lines precisely captures DEMUX behavior and synthesizes to combinational logic when the sensitivity list is complete. While concurrent conditional signal assignments can also work, the process form most exactly mirrors the algorithmic description used in textbooks and makes mutual exclusivity explicit.

Step-by-Step Solution:

Verification / Alternative check:
Simulation waveforms from a process-based DEMUX match the expected truth table. Synthesis reports infer simple gates and do not add storage elements.

Why Other Options Are Wrong:

• function: Returns a value; not ideal for driving multiple outputs directly.
• variable type: A data type, not behavior.
• a set of conditional signal assignments: Possible, but less explicit/centralized than a single process describing the DEMUX algorithm.

Common Pitfalls:
Leaving outputs unassigned in some branches (causes unintended latches); forgetting to include all signals in the sensitivity list for combinational behavior.

Final Answer:
process