Siemens S7-1200 System Manual page 398

Extended instructions
8.7 Recipes and Data logs
Network 3 A positive edge signal triggers when to store new process values in the MyData
structure.
Network 4 The EN input state is based upon when the DataLogCreate operation is complete.
A create operation extends over many scan cycles and must be complete before executing a
write operation. The positive edge signal on the REQ input is the event that triggers an
enabled write operation.
Network 5 Close the data log once the last record has been written. After executing the
DataLogWrite operation that writes the last record, the log file full status is signaled when
DataLogWrite STATUS output = 1.
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S7-1200 Programmable controller
System Manual, 03/2014, A5E02486680-AG