# IEC look-ahead carry generator (CPG) Canonical URL: https://eloragrid.ai/symbols/iec-look-ahead-carry-generator Publisher: Elora Grid Updated: 2026-10-28 Lookup label: CPG Drawing use: Schematic Reference families: IEC, Manufacturer ## Symbol convention Convention: IEC Form: Rectangular element with CPG qualifier 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. IEC element marked CPG that computes carries for several adder stages at once to speed up arithmetic. ## In plain English ### What does IEC look-ahead carry generator (CPG) mean? 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. ### A simple 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. ### What the drawings help you do 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. ### This particular reference 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. ### 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 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. ## How to read it - Generate and propagate lines come from each arithmetic stage. - Carries return to each stage in parallel. ## Information to show or reference - Mark the element CPG. - Label generate, propagate and carry lines per stage. - Show the stage count. ## Important distinction A ripple-carry arrangement chains CO to CI directly with no CPG element. ## Facts - Qualifier: CPG - Purpose: Parallel carry calculation - 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. Lists CPG as the look-ahead carry generator qualifier. ## 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.