Data Exchange - OPC UA Server
For identifications of the items the OPC UA server can use either data point or data point element names or data point aliases. Using aliases the user can realize an addressing via OPC UA independent from the WinCC OA data point name. Whether data point names or aliases are used has to be defined by the config entry nodeIdType. It is not allowed to mix one type with the other, i.e. the server can only use either names or aliases.
It is recommended to start only one WinCC OA OPC UA server in a WinCC OA project, since the data point groups cannot be set for each server. In case that several WinCC OA OPC UA servers are started they would access the same data points.
Mapping of OPC UA <-> WinCC OA Attributes
There are two distinguishable points when mapping the WinCC OA structure to the OPC UA server process image. On the one hand the server needs the WinCC OA project structure to construct the name space and on the other hand the OPC UA server needs the data from the process image of the Event Manager.
The first data is listed in the table below. In order to keep the data on the server up-to-date the server reacts to changes of the project structure. That means that the server evaluates the corresponding WinCC OA messages.
| OPC UA Name | Data Type | Comment | Counterpart in WinCC OA |
|---|---|---|---|
| NodeId | NodeId | String | Data point name or alias. |
| NodeClass | NodeClass | Number of NodeClass | None. |
| BrowseName | QualifiedName | Node name | Data point element name (not multi-lingual). |
| DisplayName | LocalizedText | Display text of the Nodes | Data point element name (not multi-lingual). |
| Description | LocalizedText | Description |
Description in the current language of the _common WinCC OA config. If this does not exist, the DisplayName is used. |
WinCC OA -> OPC UA Varaibles
The data from the process image of the WinCC OA Event Manager is mapped to OPC UA variables. The assignment between WinCC OA attributes and the OPC UA variable attributes is listed in the following table.
| Name | Data Type | Comment | Counterpart in WinCC OA |
|---|---|---|---|
| Value | The real value |
Online value (_online.._value). If a value change is sent by the OPC UA client, the original value instead of the online value is set. |
|
| Timestamp | WinCC OA attribute _online.._stime(source time). | ||
| Status |
WinCC OA attribute _online.._status64. The proper mapping of the WinCC OA status to OPC UA status is described in the "WinCC OA status mapping to OPC UA status" paragraph below. |
||
| DataType | NodeId | See mapping of data types. | |
| ArraySize | Int32 | See mapping of data types. | |
| AccessLevel | Byte | Is defined by the data point group. For data, which is readable only, the CurrentRead flag is set. For data, which is readable and writable, CurrentRead and CurrentWrite is set. | |
| UserAccessLevel | Byte | The UserAccessLevel equals to the AccessLevel. That means the definition of the access rights takes place only via data point groups. All clients that are permitted to connect to the OPC UA server have the same access rights to the process image. |
WinCC OA status mapping to OPC UA status
WinCC OA -> OPC UA
|
If at least one of the following status bits is set: _out_prange _out_range _exp_inv _auth_inv _stime_inv |
OpcUa_Bad |
| In all other cases | OpcUa_Good |
OPC UA -> WinCC OA
| OpcUa_Good | 0 |
| OpcUa_BadXXX | WinCC OA status bit auth_inv is set |
Analog Item object
The Analog Item Object is currently not supported. Therefore, the OPC UA server does not support a relative deadband for monitored items.
Mapping of WinCC OA <-> OPC UA Data Types
The following table lists the WinCC OA data types that are supported by the WinCC OA OPC UA server. They also contain the assigned OPC UA type.
| OPC UA Data Type | WinCC OA Data Type |
|---|---|
| Boolean | DPEL_BOOL |
| Int32 | DPEL_INT |
| Int64 | DPEL_LONG |
| UInt64 | DPEL_BIT64 |
| Byte | DPEL_CHAR |
| UInt32 | DPEL_UINT |
| UInt64 | DPEL_ULONG |
| Double | DPEL_FLOAT |
| String | DPEL_STRING |
| DateTime | DPEL_TIME |
| ByteString | DPEL_BLOB |
| UInt32 | DPEL_BIT32 |
| NodeId | DPEL_DPID |
| LocalizedText | DPEL_LANGSTRING |
| Array of the basic type |
DPEL_DYN_* Note: * .. represents a basic data type
Restriction: Only an array length of up to 65536 is supported.)
|
Therefore it is not possible for the client to write a NodeId, which does not correspond to an existing DP Identifier. So these OPC UA variable nodes accept only NodeIds, which contains existing DP names.
