The enable input on a multiplexer acts like a master on/off switch for the entire chip.

Core function (short answer)

  • When the enable input is active (depending on the chip, this might mean logic 1 for active-high or logic 0 for active-low), the multiplexer works normally:
    it routes one selected data input to the output based on the select lines.

  • When the enable input is inactive , the multiplexer is effectively disabled:
    the output is forced to a fixed state (often logic 0 or high‑impedance), and the input selection logic is ignored.

Why it’s useful

  • It lets you turn the whole MUX on or off without changing the select lines or data inputs.
  • It allows multiple multiplexers to share a bus: only the enabled one drives the output, while the others are disabled so they don’t interfere.
  • It provides a simple way to gate or pause signal flow in larger digital systems.

Active-high vs active-low

  • Active-high enable : the MUX is enabled when the enable pin is at logic 1 (connected to VCC) and disabled at logic 0.
  • Active-low enable : the MUX is enabled when the enable pin is at logic 0 (connected to GND) and disabled at logic 1 (often marked with a bar, like EN‾\overline{EN}EN, or a little bubble on the pin in the datasheet).

In short, the function of an enable input on a multiplexer chip is to activate the entire chip when asserted and deactivate it (so it stops passing any input through) when deasserted.