Mm
IEC mode dependency (M)
Dependency label Mm used to show operating modes; affected inputs and outputs act only in the selected mode.
IEC
IEC · CTR +/-
IEC up/down counter
IEC counter whose mode inputs select counting up with + or down with -, drawn with M dependency.
In plain English
What does IEC up/down counter mean?
An up/down counter is shown with a CTR additional drawing mark and a clock input labelled with both counting directions, for example 2+ and 1- under mode control. A direction input produces M1 and M2 modes, so the same clock counts up in one mode and down in the other. Load and enable functions use further dependency labels.
A simple example
Typical applications include position tracking from pulse inputs, reversible totalising and digital set-point adjustment. The drawing should identify the direction source and whether direction may change while clock pulses are present.
What the drawings help you do
The symbol does not indicate how overflow or underflow is signalled beyond any CT= outputs shown. Check ripple clock or max/min outputs on the device.
This particular reference
IEC counter whose mode inputs select counting up with + or down with -, drawn with M dependency. A single-direction CTR counter shows only + on its clock.
- 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) · SN74HC191 synchronous 4-bit up/down binary counter
IEC · CTRm element with M dependency selecting count up (+) and count down (-)
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 · CTR +/-
What it represents
An up/down counter is shown with a CTR qualifier and a clock input labelled with both counting directions, for example 2+ and 1- under mode control. A direction input produces M1 and M2 modes, so the same clock counts up in one mode and down in the other. Load and enable functions use further dependency labels.
Typical applications include position tracking from pulse inputs, reversible totalising and digital set-point adjustment. The drawing should identify the direction source and whether direction may change while clock pulses are present.
The symbol does not indicate how overflow or underflow is signalled beyond any CT= outputs shown. Check ripple clock or max/min outputs on the device.
How to read it
- Find the mode input that selects direction.
- Check CT outputs for terminal counts in each direction.
Information to show or reference
- Show both + and - functions with their mode numbers.
- Label the direction input clearly.
- Show cascade outputs for multi-stage counters.
A distinction that matters
A single-direction CTR counter shows only + on its clock.
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)
Counting up and down inputs and M dependency.
SN74HC191 synchronous 4-bit up/down binary counter
Manufacturer up/down counter documentation.
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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