# IEC synchronous binary counter (CTRm)

Canonical URL: https://eloragrid.ai/symbols/iec-synchronous-binary-counter
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: CTR4
Drawing use: Schematic
Reference families: IEC, Manufacturer

## Symbol convention

Convention: IEC
Form: Rectangular element with CTRm qualifier, common-control block and weighted outputs
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: [Synchronous binary counter](https://eloragrid.ai/symbols/synchronous-binary-counter)

IEC counter marked CTRm, where m is the bit count and the cycle length is 2 to the power m.

## In plain English

### What does IEC synchronous binary counter (CTRm) mean?

The general additional drawing mark CTRm identifies a counter with m bits and a cycle length of 2 to the power m. In IEC form the clock appears as C with a + to show counting up, and load, clear and enable inputs use dependency notation such as M1 for load mode and G for count enable. Outputs carry binary weights 1, 2, 4 and 8.

### A simple example

A reader should identify the synchronous and asynchronous inputs from their prefixes, then find the carry output, often labelled CT=15, used to cascade stages. On control drawings counters represent event totals, batch counts or divide-by-n timing.

### What the drawings help you do

The symbol does not state maximum count rate or whether the clear is synchronous, except through dependency labels. Read the prefixes carefully.

### This particular reference

IEC counter marked CTRm, where m is the bit count and the cycle length is 2 to the power m. CTR DIVm states the cycle length directly and is used for non-binary counters such as decade counters.

### 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)
- [SN74HC163 — synchronous binary counters](https://www.ti.com/lit/ds/symlink/sn74hc163.pdf)


## What it represents

The general qualifier CTRm identifies a counter with m bits and a cycle length of 2 to the power m. In IEC form the clock appears as C with a + to show counting up, and load, clear and enable inputs use dependency notation such as M1 for load mode and G for count enable. Outputs carry binary weights 1, 2, 4 and 8.
A reader should identify the synchronous and asynchronous inputs from their prefixes, then find the carry output, often labelled CT=15, used to cascade stages. On control drawings counters represent event totals, batch counts or divide-by-n timing.
The symbol does not state maximum count rate or whether the clear is synchronous, except through dependency labels. Read the prefixes carefully.

## How to read it

- CTRm gives the bit count; the cycle is 2 to the power m.
- CT=15 marks the terminal-count output used for cascading.

## Information to show or reference

- State the bit count in the qualifier.
- Label load, clear and enable with dependency notation.
- Show cascade connections between stages.

## Important distinction

CTR DIVm states the cycle length directly and is used for non-binary counters such as decade counters.

## Facts

- Qualifier: CTRm
- Cycle length: 2 to the power m
- 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 CTRm and related counter qualifiers and the contents output CT=.
- [SN74HC163 — synchronous binary counters](https://www.ti.com/lit/ds/symlink/sn74hc163.pdf) — Texas Instruments. Synchronous 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.