Understand the difference.

Compare the meaning, drawing context and source references of two entries. A similar graphic or shared abbreviation does not establish equivalence.

CTR +/-

IEC

IEC up/down counter

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.

Drawing use

Schematic

Application

Logic & signals

Reference family

IEC / Manufacturer

Form evidence

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.

A distinction that matters

A single-direction CTR counter shows only + on its clock.

Full referenceAdd to legend

Mm

IEC

IEC mode dependency (M)

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.

Drawing use

Schematic

Application

Logic & signals

Reference family

IEC / Manufacturer

Form evidence

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.

A distinction that matters

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

Full referenceAdd to legend

Original educational previews. Follow the source references on each full entry for the appropriate standard or selected product.