# IEC adder (Σ)

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

## Symbol convention

Convention: IEC
Form: Rectangular element with Σ qualifier, P and Q inputs, CI and CO
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: [Binary full adder](https://eloragrid.ai/symbols/binary-full-adder)

IEC element marked Σ that adds binary words P and Q with carry-in CI and carry-out CO.

## In plain English

### What does IEC adder (Σ) mean?

The adder additional drawing mark is the capital sigma. Inputs are grouped into P and Q words with binary weights, plus a carry input CI; outputs give the sum with weights and a carry output CO. TI's overview lists Σ alongside P-Q for subtraction and CPG for look-ahead carry generation.

### A simple example

Adders on drawings usually belong to arithmetic sections of logic boards, counters with preset arithmetic, or illustrations of PLC arithmetic blocks. The carry chain between stages should be drawn so that the word length is obvious.

### What the drawings help you do

The symbol does not state whether the device uses ripple or look-ahead carry internally. Speed depends on that and on the word length.

### This particular reference

IEC element marked Σ that adds binary words P and Q with carry-in CI and carry-out CO. A subtracter carries the P-Q additional drawing mark instead; Σ marks an adder.

### 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)
- [CD74HC283 — binary full adders](https://www.ti.com/product/CD74HC283)


## What it represents

The adder qualifier is the capital sigma. Inputs are grouped into P and Q words with binary weights, plus a carry input CI; outputs give the sum with weights and a carry output CO. TI's overview lists Σ alongside P-Q for subtraction and CPG for look-ahead carry generation.
Adders on drawings usually belong to arithmetic sections of logic boards, counters with preset arithmetic, or illustrations of PLC arithmetic blocks. The carry chain between stages should be drawn so that the word length is obvious.
The symbol does not state whether the device uses ripple or look-ahead carry internally. Speed depends on that and on the word length.

## How to read it

- Check carry-in and carry-out connections between stages.
- Bit weights define the word order.

## Information to show or reference

- Mark the element with Σ.
- Label P, Q, CI and CO.
- Show the carry chain for multi-device words.

## Important distinction

A subtracter carries the P-Q qualifier instead; Σ marks an adder.

## Facts

- Qualifier: Σ
- Carry terminals: CI and CO
- 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 Σ as the adder qualifier.
- [CD74HC283 — binary full adders](https://www.ti.com/product/CD74HC283) — Texas Instruments. Binary full adder 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.