Siemens Step 7 question

[haygood2]

What is significant about FB80 and why is important to load this block even though nothing is in it??

 

[Macbeth]

I use step7 all the time and I can say, I have never had to do that. What happens if you do not load FB80?

 

[haygood2]

OB80 is a scan cycle time fault

If your preset scan cycle time is exceeded and you don't have OB80 loaded, your CPU will STOP

 

[Macbeth]

Yes OB80 will do that. I should have known OB80 not FB80. The default scan tine is 150ms; you can go into CPU proprieties and change the default to a greater time. Look at CPU info to see what your actual time is.
Many of the OB’s are for error handling, when an error occurs like excessive scan time these OB are called. They allow the user to set up error handling, even though there may not be any logic in them they are still call much like an FB would. If they don’t exist the PLC won't know how to handle the error and Fault. We have often set up attribute to send messages or even counters to log such events.