Digital Design Fundamentals·Signals, Bits & Logic

Building with Gates (The 2-Input Multiplexer)

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One output, two sources

A processor constantly chooses between values: the result of an add or the result of a subtract, data from cache or data from memory. The circuit that chooses is the multiplexer, or MUX.

The trapezoid MUX symbol with data inputs a and b entering the left side, the select signal s entering from below

A 2-to-1 MUX has:

Two data inputs, a and b
One select input, s
One output, y

The rule: s = 0 routes a to the output. s = 1 routes b.