# IEC control dependency (C)

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

## Symbol convention

Convention: IEC
Form: Control input labelled Cm with affected data inputs labelled mD, mJ, mK and similar
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 label Cm on a clock or control input; inputs prefixed with m act only when Cm is active.

## In plain English

### What does IEC control dependency (C) mean?

C dependency identifies a control input, usually a clock, and the inputs it controls. Data inputs labelled 1D, 1J or 1S act only when C1 is at its internal 1 state, or on its active transition if C1 has a dynamic mark. TI's overview notes that synchronous inputs are recognisable by these dependency prefixes.

### A simple example

Reading C dependency correctly is the key to understanding flip-flops, latches, registers and counters drawn in IEC form. Inputs without the prefix, such as a plain R, are asynchronous and act regardless of the clock.

### What the drawings help you do

The label does not tell you setup and hold times or clock frequency limits. Those remain device data. Trace each prefixed data input to the numbered control before deciding whether it can change the stored state asynchronously.

### This particular reference

Dependency label Cm on a clock or control input; inputs prefixed with m act only when Cm is active. EN acts on outputs; C dependency acts on inputs.

### 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

C dependency identifies a control input, usually a clock, and the inputs it controls. Data inputs labelled 1D, 1J or 1S act only when C1 is at its internal 1 state, or on its active transition if C1 has a dynamic mark. TI's overview notes that synchronous inputs are recognisable by these dependency prefixes.
Reading C dependency correctly is the key to understanding flip-flops, latches, registers and counters drawn in IEC form. Inputs without the prefix, such as a plain R, are asynchronous and act regardless of the clock.
The label does not tell you setup and hold times or clock frequency limits. Those remain device data. Trace each prefixed data input to the numbered control before deciding whether it can change the stored state asynchronously.

## How to read it

- Inputs with the C number as prefix are synchronous.
- Inputs without the prefix are asynchronous overrides.

## Information to show or reference

- Label clock inputs as Cm.
- Prefix synchronous inputs with m.
- Mark the clock input dynamic where edge-triggered.

## Important distinction

EN acts on outputs; C dependency acts on inputs.

## Facts

- Affecting input at 1: Permits action
- Affecting input at 0: Prevents action
- 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. C (control) dependency and use with storage elements.

## 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.