ALU
IEC arithmetic logic unit (ALU)
IEC element marked ALU, performing arithmetic or logic functions on two words as chosen by mode inputs.
IEC
IEC · CPG
IEC look-ahead carry generator (CPG)
IEC element marked CPG that computes carries for several adder stages at once to speed up arithmetic.
In plain English
What does IEC look-ahead carry generator (CPG) mean?
The CPG additional drawing mark identifies a look-ahead carry generator. It takes carry generate and carry propagate signals from several adder or ALU stages and produces their carry inputs in parallel, avoiding the delay of a rippling carry chain.
A simple example
On block diagrams of arithmetic sections the CPG sits beside a row of ALUs, with generate and propagate lines going in and carry lines coming out. Recognising it explains why carries do not pass directly from one ALU to the next.
What the drawings help you do
The symbol does not indicate how many stages it serves; count the input groups or refer to the device data. Label the carry input and output ordering explicitly so the arithmetic stages cannot be connected in the wrong significance order.
This particular reference
IEC element marked CPG that computes carries for several adder stages at once to speed up arithmetic. A ripple-carry arrangement chains CO to CI directly with no CPG element.
- 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 CPG 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 · CPG
What it represents
The CPG qualifier identifies a look-ahead carry generator. It takes carry generate and carry propagate signals from several adder or ALU stages and produces their carry inputs in parallel, avoiding the delay of a rippling carry chain.
On block diagrams of arithmetic sections the CPG sits beside a row of ALUs, with generate and propagate lines going in and carry lines coming out. Recognising it explains why carries do not pass directly from one ALU to the next.
The symbol does not indicate how many stages it serves; count the input groups or refer to the device data. Label the carry input and output ordering explicitly so the arithmetic stages cannot be connected in the wrong significance order.
How to read it
- Generate and propagate lines come from each arithmetic stage.
- Carries return to each stage in parallel.
Information to show or reference
- Mark the element CPG.
- Label generate, propagate and carry lines per stage.
- Show the stage count.
A distinction that matters
A ripple-carry arrangement chains CO to CI directly with no CPG element.
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 CPG as the look-ahead carry generator 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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