# IEC common-control block

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

## Symbol convention

Convention: IEC
Form: Notched block above an array of elements
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.

Notched block above an array; its inputs apply to every element below unless dependency notation limits them.

## In plain English

### What does IEC common-control block mean?

TI's overview of IEEE Std 91 describes the common-control block as the only distinctively shaped outline used in the IEC system. It sits above an array of elements, and an input to it is an input to every element below unless dependency notation states otherwise. Clocks, clears and enables of multi-bit registers are typically drawn here.

### A simple example

When reading a register or latch symbol, start with the common-control block: it shows which signals act on all bits. The elements below then show only the per-bit data inputs and outputs, which keeps an octal device readable on one sheet.

### What the drawings help you do

The block itself does not define a function; the labels and dependency numbers on its inputs do. Without those labels it is not possible to tell whether an input is a clock, an enable or a mode control.

### This particular reference

Notched block above an array; its inputs apply to every element below unless dependency notation limits them. The common-output element has a double line and collects outputs below an array.

### 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

TI's overview of IEEE Std 91 describes the common-control block as the only distinctively shaped outline used in the IEC system. It sits above an array of elements, and an input to it is an input to every element below unless dependency notation states otherwise. Clocks, clears and enables of multi-bit registers are typically drawn here.
When reading a register or latch symbol, start with the common-control block: it shows which signals act on all bits. The elements below then show only the per-bit data inputs and outputs, which keeps an octal device readable on one sheet.
The block itself does not define a function; the labels and dependency numbers on its inputs do. Without those labels it is not possible to tell whether an input is a clock, an enable or a mode control.

## How to read it

- Read the control block first, then the per-bit elements.
- Dependency numbers decide which bits each control affects.

## Information to show or reference

- Draw the notched shape distinct from ordinary elements.
- Label each control input with its function and dependency number.
- Show only per-bit signals on the elements below.

## Important distinction

The common-output element has a double line and collects outputs below an array.

## Facts

- Outline: Notched block, unique in the IEC system
- Typical inputs: Clock, clear, enable
- 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. Describes the common-control block and how its inputs apply to the array.

## 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.