View source for IBH Link UA:Consistent Reading/Writing arrays and structures

==Consistent Reading/Writing arrays and structures from data blocks==


=== Arrays und Structures within data blocks ===


Simple arrays and structures are displayed as a variable with all values. This is only possible as long as the structure does not contain further substructures (i.e. the last Level), otherwise it will be displayed as a directory:


[[Image:IBH_Link_UA_DB_Structure_Simple.png|747px]]


Sample of a data block created with TIA Portal:


[[Image:IBH_Link_UA_DB_Structure_Array.png|475px]]



==== Reading the Variable: Consistent ====

Data can only be read consistently from a PLC if all the data of a structure fits in a telegram (PDU size).


The telegram size can be different. If a structure can be read or written consistently, the value of the variable '' 'Consistent' '' will be set to '' 'true' ''. As long the structure or size of the CPU does not change, the value of the variable will not change. That means the value must be evaluated only once during commissioning.


[[Image:IBH_Link_UA_DB_Structure_Array_Client.png|1156px]]


Data can only be read consistently from a PLC, if all the data of a structure fits in a telegram (PDU size). This allows the OPC UA client very confortable and safe to check the consistency of the data.