Powerlink - 5.2 Modeling concepts

5.2.1 POWERLINK Objects and their attributes

One of the very significant differences between POWERLINK and OPC UA is that OPC UA provides metadata to each object directly through the Server, whereas POWERLINK can transport metadata only through XDD files or specification documents. Table 9and Table 10show examples for object definitions in the POWERLINK Communication Profile EPSG DS 301.

Table 9– Example for the description of Objects in POWERLINK specifications

Index	1006h	Object Type	VAR
Name	NMT_CycleLen_U32
Data Type	UNSIGNED32	Category	M
Value Range	refer below	Access	rws, valid on reset
Default Range	-	PDO Mapping	No

Table 10– Example for the description of SubObjects in POWERLINK specifications

Sub-Index	09h
Name	Prescaler_U16
Data Type	UNSIGNED16	Category	MN: M, CN: O
Value Range	0, 1-1000	Access	rws, valid on reset
Default Range	2	PDO Mapping	No

Figure 14shows the same information in the XDD format defined in EPSG DS311.

Figure 14– Example for XDD format

Table 11lists the attributes that are specified for POWERLINK Objects, and how they are mapped to OPC UA mechanisms.

Table 11– Mapping of attributes

POWERLINK Attribute	Description
Index	Index and Sub-Index are provided by the Information Modelas Propertiesof the Objectsas defined in 5.2.2, 5.2.3and 5.2.4.
SubIndex
Name	The name of the POWERLINK Objectshall be used as the BrowseNameand the DisplayNameof the OPC UA Node
Object Type	The relevant object types of POWERLINK are VAR, ARRAY and RECORD. The VariableTypes PowerlinkArrayType, PowerlinkRecordTypeand PowerlinkVariableTypeare used to represent such objects from the POWERLINK Object Dictionaryand extend the BaseDataVariableTypeby POWERLINK specific information about the object. POWERLINK Objects of the type ARRAY shall be modelled asPowerlinkArrayType(5.2.2) POWERLINK Objectsof the type RECORD shall be modelled as PowerlinkRecordType(5.2.3) POWERLINK Objectsof the type VAR shall be modelled as PowerlinkVariableType(5.2.4)
Data Type	The mapping of primitive datatypes is defined in Table 22. In certain cases the Information Modelmakes an exception and uses a Structure DataTypeto improve the usability. Examples for such exceptions: PowerlinkErrorEntryDataType(7.5.1), encoded as DOMAIN in POWERLINK PowerlinkPDOMappingEntryDataType(7.5.3), encoded as UINT64 in POWERLINK Also for usability reasons some variables are modelled as Enumeration. Examples for such cases: NMT_CurrNMTState_U8 (PowerlinkNMTStateEnumeratioin) NMT_ResetCmd_U8 (PowerlinkNMTResetCmdEnumeration)
Value Range	The Value Range of the POWERLINK Objectcan be provided by the optional Property Rangeof the PowerlinkVariableType(5.2.4).
Category	POWERLINK defines the 3 categories Mandatory (M), Optional (O) and Conditional (Cond). OPC UA defines the ModellingRulesMandatory and Optional. Since OPC UA does provide an ModellingRulewhich can be mapped to Conditional of POWERLINK, the mapping is the following: Category M becomes the ModellingRule Mandatory Category O becomes the ModellingRule Optional Category Cond becomes the ModellingRule Optional and requires a textual description at the objects definition about the condition that makes the object mandatory.
Access	Access and PDO Mapping are provided by the Property PowerlinkAttributesdefined for the PowerlinkVariableType(5.2.4).
PDO Mapping
Default Value	The default value of the object is provided by the optional Property DefaultValueof the PowerlinkVariableType(5.2.4).

5.2.2 PowerlinkArrayType

The VariableType PowerlinkArrayTypeis formally defined in Table 12and represents POWERLINK Objectsof the type ARRAY as defined in 5.2.

Table 12– PowerlinkArrayType Definition

Attribute		Value
BrowseName		PowerlinkArrayType
IsAbstract		False
ValueRank		1 (1 = OneDimension)
DataType		BaseDataType
References	NodeClass		BrowseName	DataType	TypeDefinition	ModellingRule	Access Level
Subtype of BaseDataVariableTypedefined in OPC 10000-5.
HasProperty	Variable		PowerlinkAttributes	PowerlinkAttributes	PropertyType	Mandatory	Read
HasProperty	Variable		Index	UInt16	PropertyType	Mandatory	Read
HasProperty	Variable		NumberOfEntries	Byte	PropertyType	Mandatory	Read / Write
HasProperty	Variable		Range	Range	PropertyType	Optional	Read
HasProperty	Variable		DefaultValue	BaseDataType	PropertyType	Optional	Read

The Property PowerlinkAttributesprovides the information of the XML-Attribute ‘accessType’ from the POWERLINK XML Device Description.

The Property Indexprovides the Index of the object in the POWERLINK Object Dictionary.

The Property NumberOfEntriesprovides the value of Sub-Index 0 of the POWERLINK Object. For most POWERLINK Objectsthis value is read-only. For a few, like ERR_History_ADOMor PDO_RxMappParam_XXh_AU64, this Propertyis also writable.

The optional Property Rangeprovides the Value Range of the array elements.

The optional Property DefaultValue provides the default value of the array elements. The DataTypeof this Propertyshall be identical to the DataTypeof the DataVariableitself.

5.2.3 PowerlinkRecordType

The VariableType PowerlinkRecordTypeis formally defined in Table 13and represents POWERLINK Objectsof the type RECORD as defined in 5.2.

Table 13– PowerlinkRecordType Definition

Attribute		Value
BrowseName		PowerlinkRecordType
IsAbstract		True
ValueRank		-1 (-1 = Scalar)
DataType		Byte
Value		0
References	NodeClass		BrowseName	DataType	TypeDefinition	ModellingRule	Access Level
Subtype of BaseDataVariableTypedefined in OPC 10000-5.
HasProperty	Variable		Index	UInt16	PropertyType	Mandatory	Read
HasProperty	Variable		NumberOfEntries	Byte	PropertyType	Mandatory	Read

The Property Indexprovides the Index of the object in the POWERLINK Object Dictionary.

The Property NumberOfEntriesprovides the value of Sub-Index 0 of the POWERLINK Object.

5.2.4 PowerlinkVariableType

The VariableType PowerlinkVariableTypeif formally defined in Table 14and represents POWERLINK Objectsof the type VAR as defined in 5.2.

Table 14– PowerlinkVariableType Definition

Attribute		Value
BrowseName		PowerlinkVariableType
IsAbstract		False
ValueRank		-1 (-1 = Scalar)
DataType		BaseDataType
References	NodeClass		BrowseName	DataType	TypeDefinition	ModellingRule	Access Level
Subtype of BaseDataVariableTypedefined in OPC 10000-5.
HasProperty	Variable		PowerlinkAttributes	PowerlinkAttributes	PropertyType	Mandatory	Read
HasProperty	Variable		Index	UInt16	PropertyType	Mandatory	Read
HasProperty	Variable		SubIndex	Byte	PropertyType	Mandatory	Read
HasProperty	Variable		Range	Range	PropertyType	Optional	Read
HasProperty	Variable		DefaultValue	BaseDataType	PropertyType	Optional	Read

The Property PowerlinkAttributesprovides the information of the XML-Attribute ‘accessType’ from ‘Object’ and ‘SubObject’-Elements in the POWERLINK XML Device Description. The DataType PowerlinkAttributesis formally defined in 7.3.1.

The Properties Index and SubIndexprovide the address information of the object in the POWERLINK Object Dictionary.

The optional Property Rangeprovides the Value Range of the POWERLINK Object.

The optional Property DefaultValue provides the default value of the POWERLINK Object. The DataTypeof this Propertyshall be identical to the DataTypeof the DataVariableitself.

Note 1 to entry:

The PropertiesIndex and SubIndex serve two purposes. It is not only additional information for the Client, but it also allows a generic implementation to interpret an imported Information Modelbecause it already provides the required addressing information.