Where do online blocks get symbols from if no UDTs exist online?

[plcnoob69]

I'm a bit confused about how symbols and UDTs work...
As far as I know, in offline mode FB gets symbols from the UDT declared in the "state" variables section on top. When you download FB and go online, you can still see the symbols. Where does it get them from?

One more thing I'm confused about is that if you make a change to UDT and copy online FB to the offline project, you will get STAT everywhere because of timestamp conflict. Is there not a way to tell the FB to ignore the timestamp, or is there another way to recover the symbols in such a case?

 

[mk42]

What PLC are you using? The answer could change a lot based on the PLC. I'm assuming it's a Siemens one, S7-300?

 

[plcnoob69]

Yes that is correct

 

[mk42]

I'm a bit confused about how symbols and UDTs work...
As far as I know, in offline mode FB gets symbols from the UDT declared in the "state" variables section on top. When you download FB and go online, you can still see the symbols. Where does it get them from?

It's been a while, but I think that as long as the block interface didn't change, Step 7 keeps the offline copy of the symbols. Or, if you're talking about global tags (I/Q/M/etc) then those come from the symbol table.

One more thing I'm confused about is that if you make a change to UDT and copy online FB to the offline project, you will get STAT everywhere because of timestamp conflict. Is there not a way to tell the FB to ignore the timestamp, or is there another way to recover the symbols in such a case?

never tried that part, no idea, sorry

 

[RVaughan]

Assuming S7-300/S7-400:
When you view online blocks, you are viewing them through the lens of the offline project. The raw code is uploaded to your computer, then Step7 matches the offline names with the online code and finally displays it on your screen.

You may view the online code through Accessible nodes to view without the lens of the offline project.