Hello,

Give more details. How did you solved SF error then? Did you check what means this SF in diagnostic? What kind of CPU do you use? Of course, (depends what means SF) you could use memory card, battery...instead of UPS.

Regards,

Hristo Mihalev

Hello,
Also please tell us more details if you have a profibus network linked with the CPU.
Regards,

Hello mef3000,
Ok, Let me descripe your problem in other words.
When you power off the complete system (i.e. the PLC and the profibus nodes and then power on them again, Each node needs few seconds in order to aquire its bus parameter. The CPU it self also take a time (few seconds) to be in run mode. What will happen if the CPU has come to run mode faster than the profibus slaves?
It would give bus fault (BF).

I do recommend you to insert OB86 in your program. Here's bellow OB86 description:

The operating system of the CPU calls OB86 whenever the failure of a central expansion rack (not with S7-300), a DP master system, or a station is detected in the distributed I/Os (PROFIBUS DP or PROFINET IO) (both when entering and outgoing event).

If OB86 has not been programmed, the CPU changes to the STOP mode when this type of error is detected.

You can disable or delay and re-enable OB86 using SFCs 39 to 42.

Regards,