# Overview

## Task

The CNC commands M and H are used to command machine switching and auxiliary functions via the PLC.

- Some of the M functions are defined by standardisation.
- Users can freely use H functions and all other functions.

## Characteristics

By default, the PLC assigns M and H functions to the CNC channel in which they are programmed. In addition, these functions can be output to the PLC in an axis-specific range. This makes it simpler especially in systems with

- several CNC channels and
- together with the axes used by the functions

in order to implement PLC applications.

## Parametrisation

CNC channels are each parameterised via an initialisation list (see Channel parameter list). All M and H functions must be specified here. Instead of a channel-specific assignment, an axis-specific assignment and a synchronisation method can be defined.

At the interface to the PLC (High Level Interface) [HLI], M and H functions are output in the channel and axis-specific areas and the PLC further processes them and confirms them accordingly.

A complete list of parameters described in this document is contained in the chapter Parameters.

## Programming

M and H functions are programmed in compliance with DIN 66025. The M/H function is output at the channel-specific part of the HLI.