Simantic S7 manager uses DB, OB, FC, PB and FB
OBs : Determine the structure of the user program
Data Block : These are the blocks used by logic blocks in CPU program for storing the data. DB’s doesnot contain any instructions and it take up space in the user memory. The user program can access a data block with bit, byte, word or double word operations.
Global data block : These contains information that can be accessed by all the logic block in the user program.
Instance data block : These DBs are always assigned to a particular FB.
FC Functions : It is a logic block without memory. An FC is always executed by calling in another block. FC is used either for returning a function value to a calling function or executing a technological function. Temporary variable belonging to FC are saved in local stack and this data is lost when the FC has been executed.
Function Blocks (FBs) : A function block is block with a memory. A FB contains a program that is always executed when a different logic block calls the FB. FB make it much easier to program frequently occurring complex functions.