Siemens SIMATIC S7-400 Operating Instructions Manual page 42

Configuration and operation
4.5 Data types
You will find a general description of the coding of the data types in the STEP 7 online help.
Special features of complex data types
With the complex data types used by the OPC UA function of the CP. the special coding
rules apply that are described below.
STRING
A STRING can contain a maximum of 254 characters.
ASCII characters from the range 32 (0x20) .. 255 (0xFF) are permitted.
Of these, the following characters are not permitted: 127 (0x7F), 129 (0x81), 141 (0x8D),
143 (0x8F), 144 (0x90), 157 (0x9D)
Special features of the OPC UA server
The characters are coded in the format UTF-8 in the OPC UA server of the CP.
Special features of the OPC UA client
With process data with the data type STRING that are referenced by the "UAAnyPointer",
the data type "2" (BYTE) is specified.
As the repetition factor in the UAAnyPointer always select the maximum value of 256
(0x100); 254 for the user data + 2 for the header.
ARRAY
Special features of the OPC UA client
The client program blocks support only the transfer of one dimensional arrays from the
memory area "DB".
The transfer of the data type "ARRAY of BOOL" is not supported by the client program
blocks.
With a ARRAY of STRING, with the limits of the dimension of every string element the
maximum length (256) must be specified "n" times, where "n" is the number of strings in the
array.
Special features of the OPC UA server
The data type "ARRAY of BOOL" is readable in all cases.
The data type "ARRAY of BOOL" can only be written when the length is a multiple of 8.
UDT
You will find the structure of the UDTs required by the program blocks for the OPC UA client
function in the description of the relevant block, see for example UDT757 UAAnyPointer
(Page 99).
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Operating Instructions, 01/2017, C79000-G8976-C427-02
CP 443-1 OPC UA