# IEC T (toggle) flip-flop Canonical URL: https://eloragrid.ai/symbols/iec-t-flip-flop Publisher: Elora Grid Updated: 2026-10-28 Lookup label: 1T Drawing use: Schematic Reference families: IEC, Manufacturer ## Symbol convention Convention: IEC Form: Rectangular bistable with 1T and dynamic C1 inputs 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 bistable with a 1T toggle input; when T is active, each clock edge changes the stored state. ## In plain English ### What does IEC T (toggle) flip-flop mean? The toggle input T causes the internal state to change to its complement. In IEC form it is labelled 1T when controlled by a C1 clock, or drawn as a single dynamic T input where each transition toggles. A T stage is the basic divide-by-two element in counters and frequency dividers. ### A simple example Dedicated T flip-flop packages are rare; the function is usually built from a JK with J and K tied high or a D flip-flop with its complemented output fed back. Functional logic drawings, PLC function-block diagrams and FPGA documentation still use the T form because it states the intent clearly. ### What the drawings help you do The symbol does not show how the toggle function is implemented. Where a JK or D device is used, the physical wiring should appear on the detailed schematic. ### This particular reference IEC bistable with a 1T toggle input; when T is active, each clock edge changes the stored state. A JK flip-flop provides set, reset, hold and toggle; a T element provides only hold and toggle. ### 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 toggle input T causes the internal state to change to its complement. In IEC form it is labelled 1T when controlled by a C1 clock, or drawn as a single dynamic T input where each transition toggles. A T stage is the basic divide-by-two element in counters and frequency dividers. Dedicated T flip-flop packages are rare; the function is usually built from a JK with J and K tied high or a D flip-flop with its complemented output fed back. Functional logic drawings, PLC function-block diagrams and FPGA documentation still use the T form because it states the intent clearly. The symbol does not show how the toggle function is implemented. Where a JK or D device is used, the physical wiring should appear on the detailed schematic. ## How to read it - Read T as change state on each enabled clock. - Check the implementation on the detailed schematic. ## Information to show or reference - Label the toggle input as 1T with a C1 clock, or as a dynamic T. - Show initial state where required. - Cross-reference the implementing JK or D device. ## Important distinction A JK flip-flop provides set, reset, hold and toggle; a T element provides only hold and toggle. ## Facts - Function: Toggle on each enabled clock - Typical use: Divide-by-two, counter stage - 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. Defines the T toggle input. ## 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.