# IEC set and reset dependency (S, R) Canonical URL: https://eloragrid.ai/symbols/iec-set-reset-dependency Publisher: Elora Grid Updated: 2026-10-28 Lookup label: Sm/Rm Drawing use: Schematic Reference families: IEC, Manufacturer ## Symbol convention Convention: IEC Form: Affecting inputs labelled Sm or Rm with affected outputs labelled m 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. Dependency labels Sm and Rm: the affected output behaves as if set or reset when the affecting input is active. ## In plain English ### What does IEC set and reset dependency (S, R) mean? S and R dependencies specify the internal state of an output when both set and reset conditions could be active together. An Rm input at its internal 1 state makes the affected output react as it would to S=0, R=1; an Sm input does the opposite. At 0 they have no effect. ### A simple example These labels are used where a storage element must have a defined priority between set and reset. A reader can see from the symbol whether set or reset dominates, which matters in latching alarm and interlock logic. ### What the drawings help you do Plain S and R labels without numbers are the ordinary set and reset inputs of a bistable element. The dependency form only applies when a number follows the letter. ### This particular reference Dependency labels Sm and Rm: the affected output behaves as if set or reset when the affecting input is active. An ordinary R input resets the element directly; Rm dependency states the reaction of particular outputs. ### Terms - Normally open / normally closed: The contact state in the normal condition defined for the drawing. - 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 S and R dependencies specify the internal state of an output when both set and reset conditions could be active together. An Rm input at its internal 1 state makes the affected output react as it would to S=0, R=1; an Sm input does the opposite. At 0 they have no effect. These labels are used where a storage element must have a defined priority between set and reset. A reader can see from the symbol whether set or reset dominates, which matters in latching alarm and interlock logic. Plain S and R labels without numbers are the ordinary set and reset inputs of a bistable element. The dependency form only applies when a number follows the letter. ## How to read it - S or R followed by a number is a dependency; without a number it is an ordinary input. - Check which one dominates when both are active. ## Information to show or reference - Number dependency inputs explicitly. - Label affected outputs with the matching number. - State set or reset priority in the logic description. ## Important distinction An ordinary R input resets the element directly; Rm dependency states the reaction of particular outputs. ## Facts - Rm at 1: Output reacts as to S=0, R=1 - Sm at 1: Output reacts as to S=1, R=0 - 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. S (set) and R (reset) dependencies and the summary table. ## 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.