RAM
IEC random-access memory (RAM)
IEC element marked RAM with address grouping, a write control input and A-labelled data inputs and outputs.
IEC
IEC · ROM
IEC read-only memory (ROM)
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.
- Signal
- Electrical information passed between devices, rather than necessarily the main power supply.
- Schematic
- A drawing showing function and connections rather than physical appearance.
Read the source: Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)
IEC · 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.
Shown as an independently authored educational illustration. Use the cited publication and drawing legend to verify the required drafting form.
Schematic · ROM
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.
A distinction that matters
RAM adds write inputs; ROM outputs only.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)
Lists ROM and describes A dependency for memories.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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