# Data structure AXES_GROUP_REF

PLCopen Part4 specification defines a structure named AXES_GROUP_REF. Every FB that commands an axes group has a VAR_IN_OUT parameter of this type to be able to determine the commanded axes group. The contents of the AXES_GROUP_REF structure are specific to each manufacturer as stipulated in the PLCopen definition.

The ISG implementation, the AXES_GROUP_REF contains a variable HliIfcIdx which can be used for the axis group index which addresses an axis group-specific area on the HLI.

This axis group index is initialised once in a PLC project by the FB MCV_PlatformBase.

In addition, the structure contains an array for the last six error messages that were notified by the motion controller for an axis group. However, the structure is not defined in the “McpPlcopenP4” library but in the “McpBase” library.

## Additional information

- Array for data structures of the AXES_GROUP_REF type