STEP 7 - Operation

I read several papers on the blocks in s7 300 and wanted to know
if someone could explain more about the following blocks as the
readings of the manual does not say much:
OB: Organization block
FC: Function
FB: Function block
DB: Data block
SFC: System functions
SFB: System function block
SDB: System data block

taken from the following website: http://support.automation.siemens.c...&viewreg=WW&nodeid0=10805384&objaction=csview

some initial information that may allow progress and better understand the concepts without getting lost. thanks

Hello Rubik;
The best level of information on this subject is located in this basic document, Programming with Step 7 (see ch.4):
http://support.automation.siemens.com/WW/view/en/18652056

Basically:
-OBs are called by the operating system, not by the user. OB1 is the only one that the programmer uses to setup his program cycle;all higher numbered OBs can interrupt it if the OS requireds it. Think of a main() function in C programming.

-FCs are small blocks of programming used to setup the logic of a particular machine or operation. They are called from OB1 or another block. Think of C procedures.

-FBs are almost the same as FCs, but they have an memory block (an instance DB) attached to them permanently. They are used when it is required that you can have access to the memory area at all times in the progrmming; anything that requires counting or timing will find this useful, runtime meters and totalizers are only some uses for them.

-DBs are areas of user memory, structured for a special use by the programmer. For repetetive creation of DBs, create a UDT (user-defined type) and use that to create identical DBs as required; one example, create a UDT called MNotor control, weith all required bits, INTs and REALs needed, then create your DBs for each motor you will control.

-SFC and SFB are pre-programmed blocks (FB and FC) made available by Siemens for intricate programming: communication blocks, PIDs, diagnostics, etc.:
http://support.automation.siemens.com/WW/view/en/44240604
Not all SBCs and SFBs are available for every S7 CPU; the CPU firmware limits the selection.

-SDBs are system datablocks generated by the HWConfig editor when you create a hardware configuration for the project. The user may not open or modify them, as they may then lose consistency.
Hope this helps,
Daniel Chartier

thanks dchartier for the clarification, very didactic way of comparison with C.
Now I can go a little more in the world of the plc.
Greetings