WinCC Flexible Data logging

Hi Guys - How do I get WinCC Flexible Standard to log data when I tell it to log it. I defined the datalog and looked at the properties of tags which allow for logging on value change, cyclically and on demand but I can't see what on demand actual does or how it works?

What I want to do is log three tag variables at the same time when I raise a complete flag in the Siemens S7 315-2DP PLC.

Thanks in advance

Haven't done it yet, but looking at the help file it looks like you'll need to create an object which you tie to your "Complete" Flag. Then you need to use the change of state of this variable to execute the ArchiveVariable System Function (hope it's called that in English too).

Log Tag

I think you can call the Log_Tag event and it will log the tag. You could set this up with the on change event of a tag (end of seq) so when the tag (end of seq) changes state it would log the data.