1D
IEC D flip-flop (rectangular form)
IEC bistable with a dynamic C1 clock and a 1D data input, storing D on the active clock edge.
IEC
IEC · Cm
IEC control dependency (C)
Dependency label Cm on a clock or control input; inputs prefixed with m act only when Cm is active.
In plain English
What does IEC control dependency (C) mean?
C dependency identifies a control input, usually a clock, and the inputs it controls. Data inputs labelled 1D, 1J or 1S act only when C1 is at its internal 1 state, or on its active transition if C1 has a dynamic mark. TI's overview notes that synchronous inputs are recognisable by these dependency prefixes.
A simple example
Reading C dependency correctly is the key to understanding flip-flops, latches, registers and counters drawn in IEC form. Inputs without the prefix, such as a plain R, are asynchronous and act regardless of the clock.
What the drawings help you do
The label does not tell you setup and hold times or clock frequency limits. Those remain device data. Trace each prefixed data input to the numbered control before deciding whether it can change the stored state asynchronously.
This particular reference
Dependency label Cm on a clock or control input; inputs prefixed with m act only when Cm is active. EN acts on outputs; C dependency acts on 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 · Control input labelled Cm with affected data inputs labelled mD, mJ, mK and similar
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 · Cm
What it represents
C dependency identifies a control input, usually a clock, and the inputs it controls. Data inputs labelled 1D, 1J or 1S act only when C1 is at its internal 1 state, or on its active transition if C1 has a dynamic mark. TI's overview notes that synchronous inputs are recognisable by these dependency prefixes.
Reading C dependency correctly is the key to understanding flip-flops, latches, registers and counters drawn in IEC form. Inputs without the prefix, such as a plain R, are asynchronous and act regardless of the clock.
The label does not tell you setup and hold times or clock frequency limits. Those remain device data. Trace each prefixed data input to the numbered control before deciding whether it can change the stored state asynchronously.
How to read it
- Inputs with the C number as prefix are synchronous.
- Inputs without the prefix are asynchronous overrides.
Information to show or reference
- Label clock inputs as Cm.
- Prefix synchronous inputs with m.
- Mark the clock input dynamic where edge-triggered.
A distinction that matters
EN acts on outputs; C dependency acts on 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)
C (control) dependency and use with storage elements.
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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