# IEC retriggerable monostable

Canonical URL: https://eloragrid.ai/symbols/iec-retriggerable-monostable
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: ⊓
Drawing use: Schematic
Reference families: IEC, Manufacturer

## Symbol convention

Convention: IEC
Form: Rectangular element with the single-pulse qualifier only
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. The counterpart is the matching functional concept; no equivalence of every detailed standard graphic is asserted.
Related representation: [Retriggerable monostable](https://eloragrid.ai/symbols/retriggerable-monostable)

IEC monostable showing only the single-pulse qualifier; each new trigger restarts the output pulse.

## In plain English

### What does IEC retriggerable monostable mean?

The retriggerable monostable is marked with the single pulse shape without the preceding 1. Each trigger during the output pulse restarts the timing, so the output remains active as long as triggers arrive more often than the set period.

### A simple example

This behaviour is useful for missing-pulse detection and activity monitoring, where the output drops only when a regular signal stops. The drawing should note the expected trigger rate and the timeout chosen.

### What the drawings help you do

The symbol does not show whether a clear input truncates the pulse. Check for an R input and its polarity. Include reset behaviour in the timing chart so a missing-pulse indication can be distinguished from an externally forced clear.

### This particular reference

IEC monostable showing only the single-pulse additional drawing mark; each new trigger restarts the output pulse. The non-retriggerable form has the 1 additional drawing mark and ignores triggers during the pulse.

### 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)
- [CD74HC123 — retriggerable monostables](https://www.ti.com/product/CD74HC123)


## What it represents

The retriggerable monostable is marked with the single pulse shape without the preceding 1. Each trigger during the output pulse restarts the timing, so the output remains active as long as triggers arrive more often than the set period.
This behaviour is useful for missing-pulse detection and activity monitoring, where the output drops only when a regular signal stops. The drawing should note the expected trigger rate and the timeout chosen.
The symbol does not show whether a clear input truncates the pulse. Check for an R input and its polarity. Include reset behaviour in the timing chart so a missing-pulse indication can be distinguished from an externally forced clear.

## How to read it

- Each trigger restarts the pulse.
- Look for a clear or reset input.

## Information to show or reference

- Show the single-pulse qualifier without the 1.
- Draw timing components and state the timeout.
- State the expected trigger rate.

## Important distinction

The non-retriggerable form has the 1 qualifier and ignores triggers during the pulse.

## Facts

- Retrigger behaviour: Restarts timing
- Typical use: Missing-pulse detection
- 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 the retriggerable monostable general qualifier.
- [CD74HC123 — retriggerable monostables](https://www.ti.com/product/CD74HC123) — Texas Instruments. Retriggerable monostable device documentation.

## 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.