# IEC ripple counter (RCTRm)

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

## Symbol convention

Convention: IEC
Form: Rectangular element with the RCTRm 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. The counterpart is the matching functional concept; no equivalence of every detailed standard graphic is asserted.
Related representation: [Ripple binary counter](https://eloragrid.ai/symbols/ripple-binary-counter)

IEC counter marked RCTRm: an asynchronous ripple-carry counter with a cycle length of 2 to the power m.

## In plain English

### What does IEC ripple counter (RCTRm) mean?

RCTRm identifies an asynchronous or ripple-carry counter of m bits. Each stage clocks the next, so outputs change one after another rather than simultaneously. The clock input carries a dynamic mark, and a clear input is usually shown as an asynchronous R.

### A simple example

Ripple counters are used where outputs are not decoded together at high speed, such as long frequency dividers or simple timers. Drawing them with RCTR rather than CTR warns a reviewer that decoding several outputs together may produce brief false states.

### What the drawings help you do

The symbol does not state the cumulative delay through the stages. That depends on the logic family and the number of bits.

### This particular reference

IEC counter marked RCTRm: an asynchronous ripple-carry counter with a cycle length of 2 to the power m. CTRm counters are synchronous and all outputs change on the same clock edge.

### 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)
- [SN74HC393 — ripple binary counters](https://www.ti.com/lit/ds/symlink/sn74hc393.pdf)


## What it represents

RCTRm identifies an asynchronous or ripple-carry counter of m bits. Each stage clocks the next, so outputs change one after another rather than simultaneously. The clock input carries a dynamic mark, and a clear input is usually shown as an asynchronous R.
Ripple counters are used where outputs are not decoded together at high speed, such as long frequency dividers or simple timers. Drawing them with RCTR rather than CTR warns a reviewer that decoding several outputs together may produce brief false states.
The symbol does not state the cumulative delay through the stages. That depends on the logic family and the number of bits.

## How to read it

- RCTR warns that outputs settle in sequence.
- Avoid decoding multiple outputs without synchronisation.

## Information to show or reference

- Use RCTR for asynchronous counters.
- Show the clear input and its polarity.
- Note any decoding that relies on stable outputs.

## Important distinction

CTRm counters are synchronous and all outputs change on the same clock edge.

## Facts

- Qualifier: RCTRm
- Timing: Outputs change in sequence
- 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 RCTRm as the asynchronous ripple-carry counter qualifier.
- [SN74HC393 — ripple binary counters](https://www.ti.com/lit/ds/symlink/sn74hc393.pdf) — Texas Instruments. Ripple binary counter 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.