{"schemaVersion":1,"slug":"iec-look-ahead-carry-generator","name":"IEC look-ahead carry generator (CPG)","kind":"symbol","abbreviation":"CPG","aliases":["carry look-ahead generator","CPG element","fast carry unit"],"category":"logic-signals","drawingTypes":["Schematic"],"referenceFamilies":["IEC","Manufacturer"],"summary":"IEC element marked CPG that computes carries for several adder stages at once to speed up arithmetic.","description":["The CPG qualifier identifies a look-ahead carry generator. It takes carry generate and carry propagate signals from several adder or ALU stages and produces their carry inputs in parallel, avoiding the delay of a rippling carry chain.","On block diagrams of arithmetic sections the CPG sits beside a row of ALUs, with generate and propagate lines going in and carry lines coming out. Recognising it explains why carries do not pass directly from one ALU to the next.","The symbol does not indicate how many stages it serves; count the input groups or refer to the device data. Label the carry input and output ordering explicitly so the arithmetic stages cannot be connected in the wrong significance order."],"readingNotes":["Generate and propagate lines come from each arithmetic stage.","Carries return to each stage in parallel."],"drawingChecklist":["Mark the element CPG.","Label generate, propagate and carry lines per stage.","Show the stage count."],"distinction":"A ripple-carry arrangement chains CO to CI directly with no CPG element.","facts":[{"label":"Qualifier","value":"CPG"},{"label":"Purpose","value":"Parallel carry calculation"},{"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":"Lists CPG as the look-ahead carry generator qualifier."}],"related":["iec-arithmetic-logic-unit","iec-full-adder","binary-full-adder"],"artwork":"s28-iec-look-ahead-carry-generator","publishedOn":"2026-10-28","updatedOn":"2026-10-28","provenance":"independent-public-research","symbolVariant":{"convention":"IEC","form":"Rectangular element with CPG qualifier","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 look-ahead carry generator (CPG) mean?","introduction":"The CPG additional drawing mark identifies a look-ahead carry generator. It takes carry generate and carry propagate signals from several adder or ALU stages and produces their carry inputs in parallel, avoiding the delay of a rippling carry chain.","example":"On block diagrams of arithmetic sections the CPG sits beside a row of ALUs, with generate and propagate lines going in and carry lines coming out. Recognising it explains why carries do not pass directly from one ALU to the next.","drawings":"The symbol does not indicate how many stages it serves; count the input groups or refer to the device data. Label the carry input and output ordering explicitly so the arithmetic stages cannot be connected in the wrong significance order.","terms":[{"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":"IEC element marked CPG that computes carries for several adder stages at once to speed up arithmetic. A ripple-carry arrangement chains CO to CI directly with no CPG element.","profileId":"reviewed-symbol-20261028"},"url":"https://eloragrid.ai/symbols/iec-look-ahead-carry-generator","illustration":{"url":"https://eloragrid.ai/tools/electrical-library/illustrations/iec-look-ahead-carry-generator.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":"Lists CPG as the look-ahead carry generator qualifier."}]}