# IEC read-only memory (ROM)

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

## Symbol convention

Convention: IEC
Form: Rectangular element with ROM qualifier, address grouping and A-dependent 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.

IEC element marked ROM with grouped address inputs and data outputs that read the addressed word.

## In plain English

### What does IEC read-only memory (ROM) mean?

A ROM is drawn with the ROM additional drawing mark, usually followed by its organisation such as 256x8. Address inputs are grouped with a binary grouping bracket marked A, and data outputs carry an A label to show they deliver the addressed word. Enable inputs often control three-state outputs.

### A simple example

On control drawings ROM symbols document lookup tables, character generators or firmware storage on logic boards. The organisation figure tells a reviewer the address range and data width at a glance.

### What the drawings help you do

The symbol does not show the stored content. The content reference, such as a firmware or table file revision, should be noted next to the symbol.

### This particular reference

IEC element marked ROM with grouped address inputs and data outputs that read the addressed word. RAM adds write inputs; ROM outputs only.

### 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

A ROM is drawn with the ROM qualifier, usually followed by its organisation such as 256x8. Address inputs are grouped with a binary grouping bracket marked A, and data outputs carry an A label to show they deliver the addressed word. Enable inputs often control three-state outputs.
On control drawings ROM symbols document lookup tables, character generators or firmware storage on logic boards. The organisation figure tells a reviewer the address range and data width at a glance.
The symbol does not show the stored content. The content reference, such as a firmware or table file revision, should be noted next to the symbol.

## How to read it

- Organisation such as 256x8 gives words by width.
- Data outputs carry the A label.

## Information to show or reference

- State the organisation.
- Group address inputs with A notation.
- Reference the content revision.

## Important distinction

RAM adds write inputs; ROM outputs only.

## Facts

- Qualifier: ROM
- Notation: A dependency on data outputs
- 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 ROM and describes A dependency for memories.

## 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.