Node definitions are specified using tables (See Table 1)

Table 1 – Type Definition Table



Attribute name

Attribute value. If it is an optional Attribute that is not set “--“ will be used.







ReferenceType name

NodeClass of the TargetNode.

BrowseName of the target Node. If the Reference is to be instantiated by the server, then the value of the target Node’s BrowseName is “--“.

Attributes of the referenced Node, only applicable for Variables and Objects.

Referenced ModellingRule of the referenced Object.

Notes –

Notes referencing footnotes of the table content.

Attributes are defined by providing the Attribute name and a value, or a description of the value.

References are defined by providing the ReferenceType name, the BrowseName of the TargetNode and its NodeClass.

  • If the TargetNode is a component of the Node being defined in the table the Attributes of the composed Node are defined in the same row of the table.
  • The DataType is only specified for Variables; “[<number>]” indicates a single-dimensional array, for multi-dimensional arrays the expression is repeated for each dimension (e.g. [2][3] for a two-dimensional array). For all arrays the ArrayDimensions is set as identified by <number> values. If no <number> is set, the corresponding dimension is set to 0, indicating an unknown size. If no number is provided at all the ArrayDimensions may be omitted. If no brackets are provided, it identifies a scalar DataType and the ValueRank is set to the corresponding value (see OPC 10000-3). In addition, ArrayDimensions is set to null or is omitted. If it can be Any or ScalarOrOneDimension, the value is put into “{<value>}”, so either “{Any}” or “{ScalarOrOneDimension}” and the ValueRank is set to the corresponding value (see OPC 10000-3) and the ArrayDimensions is set to null or is omitted. In Table 2 examples are given.

Table 2 – Examples of DataTypes









omitted or NULL

A scalar Int32




omitted or {0}

Single-dimensional array of Int32 with an unknown size




omitted or {0,0}

Two-dimensional array of Int32 with unknown sizes for both dimensions





Two-dimensional array of Int32 with a size of 3 for the first dimension and an unknown size for the second dimension





Two-dimensional array of Int32 with a size of 5 for the first dimension and a size of 3 for the second dimension




omitted or NULL

An Int32 where it is unknown if it is scalar or array with any number of dimensions




omitted or NULL

An Int32 where it is either a single-dimensional array or a scalar

If the NodeId of a DataType is provided, the symbolic name of the Node representing the DataType shall be used.

If no components are provided, the DataType, TypeDefinition and ModellingRule columns may be omitted and only a Comment column is introduced to point to the Node definition.

Components of Nodes can be complex, i.e. containing components by themselves. The TypeDefinition, NodeClass, DataType and ModellingRule can be derived from the type definitions, and the symbolic name can be created as defined in Therefore those containing components are not explicitly specified; they are implicitly specified by the type definitions.

This “OPC UA for Sercos Devices Companion Specification” is mandatory using String as IdentifierType for all Objects / instance NodeIds and any NodeIds, e.g. Numeric, for the ObjectType NodeIds.

The symbolic name of each Node defined in this document is its BrowseName, or, when it is part of another Node, the BrowseName of the other Node, a “.”, and the BrowseName of itself. In this case “part of” means that the whole has a HasProperty or HasComponent Reference to its part. Since all Nodes not being part of another Node have a unique name in this document, the symbolic name is unique.

In this “OPC UA for Sercos Devices companion specification”, the Identifier for each Node starts with one out of the three possible connection / addressing types

  • Topological (defined in Sercos Communication Profile Specification).

The Sercos topology index (topological address) describes the position of a slave (device) in a Sercos network. It uses a daisy chain numeration starting with value 1 at the first slave behind the master.

  • Sercos (defined in Sercos Communication Profile Specification).

The Sercos address is a freely selectable address of a slave (device) in the range between 1 and 511. It has to be unique in the Sercos network.

  • SercosIP (defined in Sercos Internet Protocol Services Specification).

This is the IP address of a Sercos device within an IP network, e.g. Sercos network or “non-Sercos” network.

Each connection type has its own NodeId composition that can be explained as follows. Each of the following examples addresses the variable MinValue from parameter S-0-0001 (SercosParameterType).


Topological,[Sercos Master No.], [Sercos Topological Address]

e.g. Topological,0,1.ParameterSet.”S-0-0001”.MinValue


Sercos,[Sercos Master No.], [Sercos Slave Address]

e.g. Sercos,0,1.ParameterSet.”S-0-0001”.MinValue


SercosIP,[IP Address], [SlaveIndex], [SlaveExtension]

e.g. SercosIP,””,0,0.ParameterSet.”S-0-0001”.MinValue

(The SlaveIndex will be derefered to a SlaveAddress using the IDN S-0-1046. For further information please refer to the Sercos Communication Profile Specification.)

The namespace URI for Sercos Types is “”.

The namespace URI for Sercos Instances is arbitrary, e.g. “http://[]/UA/Sercos/”.

The text part of the BrowseNames for all Nodes defined in this specification is specified in the tables defining the Nodes. The NamespaceIndex for all BrowseNames defined in this specification is server specific and depends on the position of the namespace URI in the server NamespaceArray.

In order to access data of Sercos devices via OPC UA, data types and lengths are transformed between Sercos and OPC UA. Table 3 shows the data types and data lengths transformation rules between Sercos and OPC UA.

Table 3 – Transformation rules between Sercos and OPC UA



Data Type

Data Length

Data Type

Extended Character Set

1 Octet List


Floating-Point number

4 Octet


8 Octet



2 Octet


4 Octet


8 Octet


Unsigned Integer


Binary Number

1 Octet


2 Octet


4 Octet


8 Octet


Sercos Time

8 Octet


The Sercos list data types are transformed analogue to the single data types, e.g. S-0-0017 (Data type: Integer, Data length: 4 Octed list) is transformed to an array of Int32.