Identify the device – which logic circuit accepts an n-bit binary number at its inputs and asserts exactly one output line corresponding to that input value?

Introduction / Context:
Many MSI building blocks appear similar but perform distinct roles. A decoder translates a compact binary code into a one-hot output where exactly one line is asserted for a valid input value. This is foundational for address decoding, memory selection, and enabling subsystems inside digital designs.

Given Data / Assumptions:

• Inputs: an n-bit binary value.
• Outputs: 2^n lines where a single line is active at any time for valid input.
• Enable pins may gate the device on/off without changing the mapping.

Concept / Approach:
With n input bits, a decoder generates one-of-2^n outputs. For example, a 3-to-8 decoder asserts exactly one of eight outputs based on the 3-bit input. This behavior differs from an encoder (one-of-N inputs to binary code) and a demultiplexer (routes a single input signal to one of many outputs as selected, not based on the numerical value presented across multiple input bits). Understanding these distinctions is crucial when selecting parts for address decoding versus signal routing.

Step-by-Step Solution:

Verification / Alternative check:
Device datasheets (e.g., 74HC138/238) show truth tables where only one Y output is low (active) for any input combination when enabled, confirming the one-hot mapping.

Why Other Options Are Wrong:
An LED is a display element; an encoder performs the inverse function; a demultiplexer routes a single data line to one output rather than decoding a multi-bit numeric input; a “priority latch” is not a standard device for this role.

Common Pitfalls:
Confusing decoder selection with demultiplexing; overlooking active-low outputs in some families which invert the active level.

Final Answer:
decoder