# IEC mode dependency (M)

Canonical URL: https://eloragrid.ai/symbols/iec-mode-dependency-m
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: Mm
Drawing use: Schematic
Reference families: IEC, Manufacturer

## Symbol convention

Convention: IEC
Form: Mode inputs labelled Mm, often produced by binary grouping, with affected terminals labelled m
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.

Dependency label Mm used to show operating modes; affected inputs and outputs act only in the selected mode.

## In plain English

### What does IEC mode dependency (M) mean?

M dependency is used where a device has several operating modes. When an Mm input is at its internal 1 state, inputs and outputs labelled m have their normal effect; otherwise they are disabled. Mode inputs are often produced from two select lines by binary grouping, giving M0 to M3.

### A simple example

Universal shift registers and up/down counters are typical users. On the symbol, a label such as 1,4D means the input acts as data only in mode 1 and with control 4. Reading these compound labels from left to right gives the order of conditions.

### What the drawings help you do

The notation does not define what happens during a mode change. Any restrictions on changing mode while clocking are device-specific.

### This particular reference

Dependency label Mm used to show operating modes; affected inputs and outputs act only in the selected mode. A (address) dependency selects among arrays of identical elements; M selects operating modes of one element.

### Terms

- Signal: Electrical information passed between devices, rather than necessarily the main power supply.
- Rating: A value stating the conditions for which equipment is specified.
- Schematic: A drawing showing function and connections rather than physical appearance.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)](https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf)


## What it represents

M dependency is used where a device has several operating modes. When an Mm input is at its internal 1 state, inputs and outputs labelled m have their normal effect; otherwise they are disabled. Mode inputs are often produced from two select lines by binary grouping, giving M0 to M3.
Universal shift registers and up/down counters are typical users. On the symbol, a label such as 1,4D means the input acts as data only in mode 1 and with control 4. Reading these compound labels from left to right gives the order of conditions.
The notation does not define what happens during a mode change. Any restrictions on changing mode while clocking are device-specific.

## How to read it

- Decode the mode inputs before reading other labels.
- Compound labels list affecting numbers separated by commas.

## Information to show or reference

- Show the mode-select inputs and their binary grouping.
- Label affected terminals with the mode numbers.
- Tabulate the modes in a note if the symbol is complex.

## Important distinction

A (address) dependency selects among arrays of identical elements; M selects operating modes of one element.

## Facts

- Affecting input at 1: Permits action (mode selected)
- Typical device: Universal shift register
- Artwork scope: Original educational illustration; consult the applicable standard and the selected device documentation for the exact graphic

## Public references

- [Overview of IEEE Standard 91-1984: explanation of logic symbols (SDYZ001A)](https://www.ti.com/lit/ml/sdyz001a/sdyz001a.pdf) — Texas Instruments. M (mode) dependency affecting inputs and outputs.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.