EN
IEC three-state buffer (rectangular form)
IEC buffer whose output carries the three-state triangle and is controlled by an EN input.
IEC
IEC · 3S
IEC three-state output qualifier
Downward triangle inside an outline marking an output that can enter a high-impedance state.
In plain English
What does IEC three-state output qualifier mean?
The three-state additional drawing mark is a small triangle pointing downwards, drawn inside the outline next to the output. It says the output has a third, high-impedance state in addition to high and low. The output is controlled by an EN input or by EN dependency.
A simple example
Wherever this additional drawing mark appears, the reader should find the controlling EN input and confirm that only one driver on the net can be enabled at once. On bus diagrams the additional drawing mark is often shown on only the first element of an array to reduce clutter.
What the drawings help you do
The additional drawing mark does not indicate bus hold or default level when all drivers are off. A floating bus needs pull resistors or bus-keeper circuitry shown separately.
This particular reference
Downward triangle inside an outline marking an output that can enter a high-impedance state. The open-circuit diamond indicates a stage that is off in one level, not a controlled high-impedance state.
- 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 · Small downward-pointing triangle inside the outline at the output
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 · 3S
What it represents
The three-state qualifier is a small triangle pointing downwards, drawn inside the outline next to the output. It says the output has a third, high-impedance state in addition to high and low. The output is controlled by an EN input or by EN dependency.
Wherever this qualifier appears, the reader should find the controlling EN input and confirm that only one driver on the net can be enabled at once. On bus diagrams the qualifier is often shown on only the first element of an array to reduce clutter.
The qualifier does not indicate bus hold or default level when all drivers are off. A floating bus needs pull resistors or bus-keeper circuitry shown separately.
How to read it
- Find the EN input or EN dependency label that controls the output.
- In arrays, the qualifier may appear only on the first element.
Information to show or reference
- Place the triangle inside the outline next to the output.
- Show the enable source.
- Show bus defaulting components where needed.
A distinction that matters
The open-circuit diamond indicates a stage that is off in one level, not a controlled high-impedance state.
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)
Defines the three-state output qualifier and EN effects.
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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