# IEC three-state output qualifier Canonical URL: https://eloragrid.ai/symbols/iec-three-state-output-qualifier Publisher: Elora Grid Updated: 2026-10-28 Lookup label: 3S Drawing use: Schematic Reference families: IEC, Manufacturer ## Symbol convention Convention: IEC Form: 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. 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. ### Terms - 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 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. ## Important distinction The open-circuit diamond indicates a stage that is off in one level, not a controlled high-impedance state. ## Facts - States: High, low and high impedance - Controlled by: EN input or EN dependency - 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. Defines the three-state output qualifier and EN effects. ## 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.