What Is a Multiplexer?
A multiplexer (mux) is a logic circuit that selects one of several inputs and passes it to a single output. It's like a digital "many-way switch".
How Does It Work?
A mux has data inputs, one output and select lines. The binary value on the select lines determines which input connects to the output. n select lines address 2ⁿ inputs.
Select Lines
For example, in a 4-to-1 mux there are 2 select lines: "00" passes the first input, "11" the fourth input to the output. The selection is done in binary.
| Type | Inputs : Select |
|---|---|
| 2:1 | 2 inputs, 1 select |
| 4:1 | 4 inputs, 2 selects |
| 8:1 | 8 inputs, 3 selects |
Difference From a Demultiplexer (Demux)
A mux selects one of many inputs and passes it to a single output; a demux does the opposite: it routes a single input to one of several selected outputs. The two are often used together.
Where Is It Used?
Reading many sensors with a single ADC, bus sharing, signal routing and memory addressing. Common ICs: 74HC151, 74HC4051.
Common Mistakes
- Missing select line: if the select terminals are left floating, which input passes is undefined.
- Mixing analog/digital: an analog mux (4051) differs from a digital mux.
- Forgetting enable: if the enable terminal is inactive, no output is obtained.
Frequently Asked Questions
Does a mux pass analog signals?+
How many select lines does a 4:1 mux need?+
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