NEG-IN
IEC logic negation at input
Small circle where an input meets an outline: an external 0 produces the internal 1 (active) state.
IEC
IEC · NEG-OUT
IEC logic negation at output
Circle on an output edge meaning the internal 1 state of the element produces an external 0.
In plain English
What does IEC logic negation at output mean?
Output negation turns AND into NAND, OR into NOR and a buffer into an inverter. The circle sits where the output line meets the outline and states that the internal 1 state produces the external 0 state. As with input negation, a logic convention must be declared to relate this to voltage levels.
A simple example
Drafters use output negation to avoid drawing separate inverters. When a negated output feeds a negated input on the next element, the two cancel, and reviewers often simplify the drawing by removing both.
What the drawings help you do
The circle carries no information about output drive type or loading. Open-circuit or three-state behaviour needs its own additional drawing mark inside the outline.
This particular reference
Circle on an output edge meaning the internal 1 state of the element produces an external 0. An active-low output triangle states the level directly and is the data-book alternative.
- Normally open / normally closed
- The contact state in the normal condition defined for the drawing.
- Signal
- Electrical information passed between devices, rather than necessarily the main power supply.
- Rating
- A value stating the conditions for which equipment is specified.
Read the source: Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)
IEC · Small circle at the output edge of the outline
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 · NEG-OUT
What it represents
Output negation turns AND into NAND, OR into NOR and a buffer into an inverter. The circle sits where the output line meets the outline and states that the internal 1 state produces the external 0 state. As with input negation, a logic convention must be declared to relate this to voltage levels.
Drafters use output negation to avoid drawing separate inverters. When a negated output feeds a negated input on the next element, the two cancel, and reviewers often simplify the drawing by removing both.
The circle carries no information about output drive type or loading. Open-circuit or three-state behaviour needs its own qualifier inside the outline.
How to read it
- Look for double negations between elements that cancel.
- Confirm the logic convention declared for the sheet.
Information to show or reference
- Place the circle at the outline edge, not along the line.
- Declare the logic convention.
- Simplify cancelling negations where the hardware allows.
A distinction that matters
An active-low output triangle states the level directly and is the data-book alternative.
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 logic negation at an output.
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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