# IEC enable input (EN)

Canonical URL: https://eloragrid.ai/symbols/iec-enable-input
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: EN
Drawing use: Schematic
Reference families: IEC, Manufacturer

## Symbol convention

Convention: IEC
Form: Input labelled EN inside the outline
Qualifying-symbol and dependency conventions as explained in TI's public overview of IEEE Std 91-1984, which incorporates IEC 617-12 work. Independent educational drawing; not certified IEC geometry or an IEC database identifier.

Input labelled EN that enables all outputs of the element when at its internal 1 state.

## In plain English

### What does IEC enable input (EN) mean?

An input labelled EN inside the outline enables every external output of the element. At its internal 0 state, open-circuit outputs are off, three-state outputs go to high impedance and other outputs take their internal 0 state. It has no effect on inputs, according to TI's public summary of the notation.

### A simple example

When an enable affects only some outputs, the notation changes to EN dependency with a number, for example EN1 with affected outputs labelled 1. Readers should distinguish a plain EN from ENm because the scope is different.

### What the drawings help you do

The label does not show the timing needed between enable and valid output. Enable and disable times are device data. Check the enabled and disabled output conditions in the selected device truth table before connecting a shared bus.

### This particular reference

Input labelled EN that enables all outputs of the element when at its internal 1 state. A C (control) input permits action of affected inputs; EN acts on outputs.

### Terms

- Normally open / normally closed: The contact state in the normal condition defined for the drawing.
- Signal: Electrical information passed between devices, rather than necessarily the main power supply.
- Schematic: A drawing showing function and connections rather than physical appearance.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)](https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf)


## What it represents

An input labelled EN inside the outline enables every external output of the element. At its internal 0 state, open-circuit outputs are off, three-state outputs go to high impedance and other outputs take their internal 0 state. It has no effect on inputs, according to TI's public summary of the notation.
When an enable affects only some outputs, the notation changes to EN dependency with a number, for example EN1 with affected outputs labelled 1. Readers should distinguish a plain EN from ENm because the scope is different.
The label does not show the timing needed between enable and valid output. Enable and disable times are device data. Check the enabled and disabled output conditions in the selected device truth table before connecting a shared bus.

## How to read it

- A plain EN affects all outputs; ENm affects only outputs labelled m.
- Check for an external polarity mark on the EN input.

## Information to show or reference

- Write EN inside the outline at the input.
- Use ENm where scope is limited.
- Show the source of the enable signal.

## Important distinction

A C (control) input permits action of affected inputs; EN acts on outputs.

## Facts

- Scope: All outputs of the element
- Effect at internal 0: Three-state outputs high impedance
- Artwork scope: Original educational illustration; consult the applicable standard and the selected device documentation for the exact graphic

## Public references

- [Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)](https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf) — Texas Instruments. Describes the EN input and its effect on different output types.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.