Σ
IEC adder (Σ)
IEC element marked Σ that adds binary words P and Q with carry-in CI and carry-out CO.
IEC
IEC · ALU
IEC arithmetic logic unit (ALU)
IEC element marked ALU, performing arithmetic or logic functions on two words as chosen by mode inputs.
In plain English
What does IEC arithmetic logic unit (ALU) mean?
The ALU additional drawing mark identifies an element that can perform several arithmetic and logic operations on input words P and Q. Function-select inputs use M dependency or a binary grouping to choose the operation, and outputs include the result, carry and often a P=Q flag. Because the function table is large, the symbol usually refers to a table on the drawing or in the datasheet.
A simple example
ALU symbols appear in processor and controller block diagrams and in legacy logic boards. On a modern control drawing they mainly document programmable logic or explain how a processor module handles signals.
What the drawings help you do
The ALU additional drawing mark does not list the operations. A function table is essential and should be referenced explicitly. Preserve the mode-select signal names and the carry interpretation when comparing the symbol with that table.
This particular reference
IEC element marked ALU, performing arithmetic or logic functions on two words as chosen by mode inputs. The Σ element only adds; the ALU selects among many operations, including subtraction and logic functions.
- 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 ALU qualifier and mode-select inputs
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 · ALU
What it represents
The ALU qualifier identifies an element that can perform several arithmetic and logic operations on input words P and Q. Function-select inputs use M dependency or a binary grouping to choose the operation, and outputs include the result, carry and often a P=Q flag. Because the function table is large, the symbol usually refers to a table on the drawing or in the datasheet.
ALU symbols appear in processor and controller block diagrams and in legacy logic boards. On a modern control drawing they mainly document programmable logic or explain how a processor module handles signals.
The ALU qualifier does not list the operations. A function table is essential and should be referenced explicitly. Preserve the mode-select signal names and the carry interpretation when comparing the symbol with that table.
How to read it
- Find the function table referenced by the mode inputs.
- Check carry and comparison outputs.
Information to show or reference
- Mark the element ALU.
- Reference the function table.
- Show carry and flag outputs.
A distinction that matters
The Σ element only adds; the ALU selects among many operations, including subtraction and logic functions.
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 ALU as a general 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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