Siemens SIMATIC ET 200AL - Page 823

OPC UA communication
9.1 What you need to know about OPC UA
Communication
Function Manual, 12/2017, A5E03735815-AF
137
SIMATIC data type
OPC UA data type
LTIME LTIME
→ Int64
DATE DATE
→ UInt16
TIME_OF_DAY (TOD) TOD
→ UInt32
LTIME_OF_DAY (LTOD) LTOD
→ UInt64
DATE_AND_TIME (DT) DT
→ Byte[8]
LDT
DateTime
DTL
mapped as structure
CHAR CHAR
→ Byte
WCHAR WCHAR
→ UInt16
STRING
(Code page 1252 or Win-
dows-1252)
STRING
→ String
WSTRING
(UCS-2; Universal Coded
Character Set)
String
TIMER TIMER
→ UInt16
COUNTER COUNTER
→ UInt16
Arrays
A read or write job with OPC UA is always an instance of array access, i.e. it has an index
and a length, so that an individual tag is only a special case of an array (index 0 and length
1). The data type is simply sent repeatedly on the line. For the tags, the "Datatype" attribute
indicates the basic data type. The attributes "ValueRank" and "ArrayDimensions" show
whether or not you are dealing with an array and how large it is.
Structures
Structures are transferred as ExtensionObject. The S7-1500 server uses binary
representation for transmission of the ExtensionObjects over the line; the individual structure
elements come one after the other. At the front is the NodeId of the data type; this is used by
the client to establish the structure.
For the OPC UA specification <= V1.03, a client must read, decode and interpret the
complete DataTypeDictionary for this purpose (unless it has already done so offline with an
XML import).