Multiplexer

A circuit that selects one of several inputs to pass to its single output, steered by select lines.

Definition

A multiplexer (mux) routes one of several data inputs to a single output, chosen by select-line control bits. With n select lines it can choose among 2^n inputs. A demultiplexer performs the reverse, routing one input to a chosen output.

A multiplexer feeding a register is the basic pattern for choosing what a storage element loads each cycle, and buses built from multiplexers let many components share wiring. This selection role makes the mux one of the most reused structures inside any processor datapath.

Because a multiplexer can implement any Boolean function of its select lines, it is not only a routing element but a universal logic building block, and lookup-table-based programmable logic exploits exactly this. In a processor datapath, multiplexers steer operands and results between registers and functional units, and buses assembled from them let many components share limited wiring, making the mux one of the most reused structures on a chip.

Uses

• Sharing a data path among many sources.
• Implementing arbitrary logic functions from a truth table.
• Selecting register contents inside a processor datapath.

Why it matters

Multiplexers are ubiquitous building blocks for routing and selection, and they are general enough to realize any Boolean function. They let one expensive resource, such as a bus or an arithmetic unit, serve many sources under control logic.

Fusion connection

Multiplexed acquisition lets a single high-speed digitizer sample many diagnostic channels in sequence, reducing hardware while preserving coverage.