I suggest the information about problems when combining optimized and standard access should be made more obvious, the first note should contain some hint and the table too. In the table below is listed only Pointer for Structured data types and the information about a different behavior for standard access is only in a note below the table 'When optimized data is transferred to a block with the property 'Standard access', it is always transferred as copy.' As structured in/out parameters are always transferred as pointer, the required data memory is not increased more than necessary.'ДЄlways means always with no exception. On the page Programming a PLC/Creating a user program/Programming basics/Block calls/Parameter transfer of block parameters/Transfer parameter as copy or as pointer there is written:Дeclare structured data types in the 'InOut' area If possible, use the 'InOut' area in the block interface for structured tags (e.g., of data type ARRAY, STRUCT, STRING, вЂ¦). I missed that information and unfortunately the online help is somehow misleading in this point. My function block originates from a S7-300 and therefore the optimized access was off. Principally, all parameters are then transferred as copies' 'However, this does not apply if one of the blocks has the property Optimized access and the other block the property Standard access. Structured InOut parameters are not always passed by reference as one could assume. The documentation is not very clear on this issue, one must read everything thoroughly. It was caused by mixing optimized and standard FB access. The problem was solved by Siemens support. Split from Uncontrolled set/reset of 'INOUT' bits from FB. It seems to be a firmware issue in all TIA PLCs or I donвЂ™t understand what passing parameters by reference meansвЂ¦ Setting and resetting another bit using all above mentioned functions in the same DB works well if the bit is not passed to any FB. It looks to me that it is passed as copy instead and if the OP writes the tag asynchronously just when the FB is processed, the write (bit set/reset) fails and the data in the DB is overwritten when the FB call ends. The data structure (PLC data type) is passed as an InOut parameter to a FB and therefor it should be passed as a pointer by reference. As Siemens does not recommend to use this function I switched to an extra single command bit (which is more labor-consuming) and I use two events with SetBit and ResetBit functions. The bit gets not always set or reset using the function SetBitWhileKeyPressed which is very annoying and possibly dangerous. Now with TIA I do the same with S7 1500 and S7 1200 CPUs and with various basic panels. The UDT was passed to a FB as INOUT parameter. In the former STEP 7 5.5 I used a byte member of a UDT placed in a DB to display the state of a device, one of the bits of that byte was used to control the device using the WinCC function SetBitWhileKeyPressed. I have a similar experience with TIA v13.

Siemens step 7 struct extra byte