I recommend downloading and reviewing the S7-1200 / S7-1500 Style and Programming Guideline document produced by Siemens.

It describes some situations where FB and FC can be used, must be used, might be useful to use, and so on.

And of course, you are welcome to download as many Siemens sample applications to see what Siemens does in their projects with OBs/FBs/FCs.

Opinions vary widely for OBs - mostly because those who starting with Siemens on S7-300/400 were limited to a single cyclic OB (OB1).  However, with s7-1200 / s7-1500 and TIA Portal, multiple OBs can be created to help organize logic better - if it makes sense to do so.

Mina0

Hi,

I´m a new in PLC world, in my job i have some times to troubleshoot but i really confused when it comes to thr relation between all blocks like OB, FC, FB and DB.

Can you please the difference between then and when it is good to use FC or FB?

Thanks in advance,

Fayek