The definition of the objects in the previous paragraphs enables the generic access to POWERLINK Objects from the POWERLINK Communication Profiles EPSG DS 301 and EPSG DS 302. Without an extension of the Information Model the access to vendor- or profile-specific POWERLINK Objects would be only possible through the SDO Services defined in 6.2.A client would not be able to create MonitoredItems and Subscriptions to vendor-specific objects since they would not have an individual NodeId.

One way to generate individual NodeIds is to convert the vendor specific device description from POWERLINK into an OPC UA Information Model and to deploy the models of all involved POWERLINK Devices to the OPC UA Server. This might be feasible for Servers that run on the POWERLINK Device itself and represent only their own device.

This paragraph defines another, more generic way to provide individual NodeIds for random objects in a POWERLINK Object Dictionary.

For this generic access the Namespace ‘http://opcfoundation.org/UA/POWERLINK/UA/DirectAccess/’ is used.

When using NodeIds of the type OPAQUE_3 the NodeId contains information about address and DataType in binary form. Compared to String-NodeIds this format is smaller and generates less overhead when registering Nodes for Subscriptions.

To access POWERLINK Objects on a Server, which represents only one POWERLINK Object Dictionary the size of the NodeId is 4 byte and the format is defined in shown in Table 48.

Table 48 – NodeIds for single instances

Byte	Description
0	LSB of the objects POWERLINK Index
1	HSB of the objects POWERLINK Index
2	POWERLINK Sub-Index
3	DataTypeId

Byte 0, 1 and 2 are the values of the POWERLINK addressing scheme Index / Sub-Index. If the POWERLINK Object requested by Index/Sub-Index is not existing the server shall signal this case with the StatusCode Bad_NodeIdUnknown.

With byte 3 the client specifies the expected DataType of the response data by using the built-in types defined in OPC 10000-6. Allowed values are 1 to 12, as well as 15. If byte 3 is set to 12 or 15 (String or ByteString) the server shall respond with the same length like the POWERLINK Object. Otherwise, if the bit-length of the referenced POWERLINK Object is different to the bit-length of the requested DataType, the Server shall signal this case with the StatusCode Bad_NodeIdInvalid.

To access POWERLINK Objects on a Server, which represents more than one POWERLINK Object Dictionary the size of the NodeId is 6 byte and the format is defined in Table 49.

Table 49 – NodeIds for multiple instances

Byte	Description
0	LSB of the objects POWERLINK Index
1	HSB of the objects POWERLINK Index
2	POWERLINK Sub-Index
3	DataTypeId
4	POWERLINK DeviceAddress
5	POWERLINK Network

Byte 0 to 3 have the same function like in Table 48.

Byte 4 defines the Address of the device in the POWERLINK network.

Byte 5 defines the interface/network number where this device is expected. The assignment of a number to a physical interface is application specific.

When using NodeIds of type STRING_1 the NodeId contains information about address and DataType as string value. Compared to opaque NodeIds this format is easier for manual entry by the user.

The NodeId has the following form:

[[<Network>.]<DeviceAddress>.]<Index>.<Sub-Index>:<Datatype>

Network:

This parameter identifies the network and starts with “NW” followed by the decimal number of the selected network, e.g. “NW1” for the first POWERLINK network which is represented by this Server. If the parameter is omitted the selection of a network is server specific.

DeviceAddress:

This parameter identifies the POWERLINK Device within a network. It shall either be “MN” for the POWERLINK Managed Node or “CN” followed by the device address, e.g. “CN2”.

Both parameters (Network and Device) are not relevant for Servers that only implement one single POWERLINK Object Dictionary and therefore they may be omitted.

Index:

Index of the POWERLINK Object, e.g. “0x1001” for the object ERR_ErrorRegister_U8. The value shall be given as decimal string, or as hexadecimal string preceding the characters “0x”.

Sub-Index:

Sub-Index of the POWERLINK Object, e.g. “17” for accessing Sub-Index 17. The value shall be given as decimal string, or as hexadecimal string preceding the characters “0x”.

If the POWERLINK Object requested by Index/Sub-Index is not existing the server shall signal this case with the StatusCode Bad_NodeIdUnknown.

Datatype:

Requested DataType of the response data for read access or MonitoredItems. Allowed values are the names of the built-in types 1 to 12, and 15. E.g. if Datatype is “UInt64” the Server shall respond with an unsigned 64 bit integer. Capitalisation of this parameter shall be irrelevant, so “uint64” and “UInt64” shall give the same result. If Datatype is set to “String” or “ByteString” the server shall respond with the same length like the POWERLINK Object. Otherwise, if the bit-length of the referenced POWERLINK Object is different to the bit-length of the requested DataType, the Server shall signal this case with the StatusCode Bad_NodeIdInvalid.

Examples for String NodeIds:

“0x1001.0:byte” : Object ERR_ErrorRegister_U8

“NW2.CN104.24640.0:UInt16” : Object 0x6040, SubIndex 0, 16 Bit unsigned

“CN1.0x1018.1:UInt32” : VendorId_U32 in Object NMT_IdentityObject_REC