Reading Siemens S7 PLC symbol table

Question

I would like, for educational purposes, to read PLC symbols table by using libnodave (or any equivalent open-source like snap7).

Actually, when I read data from merkers, I must know in advance what kind of variable will be present in the DB, also due to the fact that libnodave reads raw bytes in sequences.

I'm searching a way to know in advance what kind of data was chosen by the plc programmer when storing data so, when I use raw bytes read, I can easily monitor variables and adapt my reading and visualization routine.

Thanks in advance.

Answer 1

A program in a S7-3xx/4xx PLC has no symbolic addressing downloaded. So Libnodave or Snap7 can't point to a symbol.

TIA and the S7-12xx/15xx PLC are different. They have symbols downloaded. But so far as i know Libnodave or Snap7 can not use these symbols yet.

A solution maybe is the export the Symboltable is Step7/TIA to an Excel or .scv file and read there the symbol with it's format and address information.

(Libnodave does not support S7-12xx/15xx, use Snap7 instead.)