Data Delta Frame DataSetMessage – OPC Unified Architecture

7.2.4.5.6 Data Delta Frame DataSetMessage

The data delta frame DataSetMessage data and the related headers are shown in Figure 36.

Figure 36 – Data Delta Frame DataSetMessage

The information for a single value in delta frame messages is larger because of the additional index necessary for sending just changed data. The Publisher shall send a key frame message if the delta frame message is larger than a key frame message.

The encoding of the data delta frame DataSetMessage structure is specified in Table 164.

Table 164 – Data Delta Frame DataSetMessage structure

Name	Type	Description
FieldCount	UInt16	Number of fields of the DataSet contained in the DataSetMessage.
DeltaFrameFields	Structure [FieldCount]	The subset of field values of the DataSet contained in the delta frame.
FieldIndex	UInt16	The index of the Field in the DataSet. The index is based on the field position in the DataSetMetaData with the configuration version defined in the ConfigurationVersion field. A Publisher shall use an index only once in a DataSetMessage.
FieldValue	BaseDataType	The field values of the DataSet. The field encoding depends on the DataSetFlags1.Field Encoding of the DataSetMessage Header defined in 7.2.4.5.4. The default encoding is Variant if bit 1 and 2 are not set.
Padding	Byte [*]	Optional padding added if the encoded DataSetMessage is smaller than the ConfiguredSize. The DataSetMessage is padded with bytes with value zero.