# IEC astable element Canonical URL: https://eloragrid.ai/symbols/iec-astable-element Publisher: Elora Grid Updated: 2026-10-28 Lookup label: G Drawing use: Schematic Reference families: IEC, Manufacturer ## Symbol convention Convention: IEC Form: Rectangular element with the G qualifier and optional waveform 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 G, an astable that produces a continuous pulse train; drawing the waveform is optional. ## In plain English ### What does IEC astable element mean? The astable element is marked with G, optionally followed by a sketch of the output waveform. It produces a free-running pulse train. Variants include !G for a synchronously starting astable and G! for one that stops only after completing a pulse, as listed in TI's public overview. ### A simple example Astable elements represent oscillators on logic diagrams: flasher circuits for indicator lamps, test pulse generators and clock sources. Where an enable input exists, its effect on the output at start and stop should be considered because the variant qualifiers describe exactly that. ### What the drawings help you do The symbol does not state frequency or duty cycle. Note those values beside the element or reference the timing components. ### This particular reference IEC element marked G, an astable that produces a continuous pulse train; drawing the waveform is optional. A monostable produces one pulse per trigger; an astable runs continuously while enabled. ### 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 astable element is marked with G, optionally followed by a sketch of the output waveform. It produces a free-running pulse train. Variants include !G for a synchronously starting astable and G! for one that stops only after completing a pulse, as listed in TI's public overview. Astable elements represent oscillators on logic diagrams: flasher circuits for indicator lamps, test pulse generators and clock sources. Where an enable input exists, its effect on the output at start and stop should be considered because the variant qualifiers describe exactly that. The symbol does not state frequency or duty cycle. Note those values beside the element or reference the timing components. ## How to read it - Check for ! before or after G, which changes start or stop behaviour. - Find frequency and duty cycle in notes or timing parts. ## Information to show or reference - Mark the element with G. - State frequency and duty cycle. - Use !G or G! where start or stop behaviour matters. ## Important distinction A monostable produces one pulse per trigger; an astable runs continuously while enabled. ## Facts - Qualifier: G - Variants: !G synchronous start, G! completes last pulse - 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 G, !G and G! astable qualifiers. ## 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.