3S
IEC three-state output qualifier
Downward triangle inside an outline marking an output that can enter a high-impedance state.
IEC
IEC · EN
IEC enable input (EN)
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.
- 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.
Read the source: Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)
IEC · 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.
Shown as an independently authored educational illustration. Use the cited publication and drawing legend to verify the required drafting form.
Schematic · EN
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.
A distinction that matters
A C (control) input permits action of affected inputs; EN acts on outputs.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)
Describes the EN input and its effect on different output types.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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