=1
IEC exclusive-NOR gate (rectangular form)
IEC =1 box with a negated output, giving the two-input equivalence or exclusive-NOR function.
IEC
IEC · =
IEC logic identity element
Element marked = whose output is active only when all inputs stand at the same logic state.
In plain English
What does IEC logic identity element mean?
The = additional drawing mark defines a logic identity function: the output is active when every input is in the same state, whether all active or all inactive. For two inputs this is the equivalence or exclusive-NOR function, but with three or more inputs it is a distinct agreement check.
A simple example
Identity elements are useful for voting and agreement logic, such as confirming that three redundant transmitters agree before allowing an action. The drawing should state what happens on disagreement, since the element only reports whether agreement exists.
What the drawings help you do
The symbol does not provide majority selection. If two-out-of-three voting is intended, a different element or a combination of AND and OR elements is needed.
This particular reference
Element marked = whose output is active only when all inputs stand at the same logic state. A negated =1 element means not exactly one active; it matches identity only for two inputs.
- 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 the = general qualifier
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 · =
What it represents
The = qualifier defines a logic identity function: the output is active when every input is in the same state, whether all active or all inactive. For two inputs this is the equivalence or exclusive-NOR function, but with three or more inputs it is a distinct agreement check.
Identity elements are useful for voting and agreement logic, such as confirming that three redundant transmitters agree before allowing an action. The drawing should state what happens on disagreement, since the element only reports whether agreement exists.
The symbol does not provide majority selection. If two-out-of-three voting is intended, a different element or a combination of AND and OR elements is needed.
How to read it
- With three or more inputs, read = as all equal, not as majority.
- Check what downstream logic does on a disagreement.
Information to show or reference
- Use = only where full agreement is intended.
- Label redundant inputs with their channel identifiers.
- Show the disagreement response on the same sheet.
A distinction that matters
A negated =1 element means not exactly one active; it matches identity only for two inputs.
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)
Defines the = logic identity qualifier.
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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