{"schemaVersion":1,"slug":"iec-open-circuit-output-h-type","name":"IEC open-circuit output, H-type (open emitter)","kind":"symbol","abbreviation":"OC-H","aliases":["overlined diamond output","open-emitter qualifier","open-source qualifier"],"category":"logic-signals","drawingTypes":["Schematic"],"referenceFamilies":["IEC","Manufacturer"],"summary":"Overlined diamond at an output: an open-emitter or open-source stage that can only drive a high level.","description":["The H-type open-circuit output is drawn as a diamond with a line above it. It can supply a relatively low-impedance H level when on and is open when off, so it needs an external pull-down. TI's public overview notes it supports a positive-logic wired-OR connection.","Open-emitter outputs are typical of emitter-coupled logic and some line drivers. On a drawing the pull-down or termination must be shown, often to a negative or termination rail rather than to ground.","The qualifier does not give the termination value or rail. Those come from the logic family's application guidance and the device datasheet."],"readingNotes":["Overline above the diamond: drives high only.","Find the pull-down or termination on the net."],"drawingChecklist":["Draw the diamond with its overline next to the output.","Show the pull-down or termination and its rail.","Avoid joining H-type and L-type outputs on one net."],"distinction":"The L-type output has its line under the diamond and drives low only.","facts":[{"label":"Drives","value":"High level only"},{"label":"Wired connection","value":"Wired-OR in positive logic"},{"label":"Artwork scope","value":"Original educational illustration; consult the applicable standard and the selected device documentation for the exact graphic"}],"references":[{"sourceId":"s28-ti-ieee91-logic-symbols","relevance":"Describes the H-type open-circuit output and wired-OR capability."}],"related":["iec-open-circuit-output-l-type","iec-three-state-output-qualifier","logic-buffer"],"artwork":"s28-iec-open-circuit-output-h-type","publishedOn":"2026-10-28","updatedOn":"2026-10-28","provenance":"independent-public-research","symbolVariant":{"convention":"IEC","form":"Diamond with overline inside the outline at the output","reference":"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."},"plainEnglish":{"title":"What does IEC open-circuit output, H-type (open emitter) mean?","introduction":"The H-type open-circuit output is drawn as a diamond with a line above it. It can supply a relatively low-impedance H level when on and is open when off, so it needs an external pull-down. TI's public overview notes it supports a positive-logic wired-OR connection.","example":"Open-emitter outputs are typical of emitter-coupled logic and some line drivers. On a drawing the pull-down or termination must be shown, often to a negative or termination rail rather than to ground.","drawings":"The additional drawing mark does not give the termination value or rail. Those come from the logic family's application guidance and the device datasheet.","terms":[{"name":"Terminal","meaning":"An identified point where a conductor connects."},{"name":"Signal","meaning":"Electrical information passed between devices, rather than necessarily the main power supply."},{"name":"Schematic","meaning":"A drawing showing function and connections rather than physical appearance."}],"diagram":"flow","steps":["Identify the device and form","Read the connections and state","Check the equipment reference"],"caption":"A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.","sources":[{"label":"Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)","url":"https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf"}],"detail":"Overlined diamond at an output: an open-emitter or open-source stage that can only drive a high level. The L-type output has its line under the diamond and drives low only.","profileId":"reviewed-symbol-20261028"},"url":"https://eloragrid.ai/symbols/iec-open-circuit-output-h-type","illustration":{"url":"https://eloragrid.ai/tools/electrical-library/illustrations/iec-open-circuit-output-h-type.svg","scope":"Original educational concept; not an official standard graphic or product footprint","license":"https://creativecommons.org/licenses/by/4.0/"},"sources":[{"id":"s28-ti-ieee91-logic-symbols","title":"Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)","publisher":"Texas Instruments","url":"https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf","type":"manufacturer","scope":"Public explanation of rectangular logic symbols, general qualifiers, input and output qualifiers, dependency notation, bistable elements and coders, consistent with IEC 617-12 work.","checkedOn":"2026-10-28","reuse":"link-only","relevance":"Describes the H-type open-circuit output and wired-OR capability."}]}