Declaring PIW and PQW in WinCC
The PIW and PQW addresses for modules are set in HWconfig, i.e., select the PLC station in the project tree, then select Hardware. This is where you define the modules on a rack. Normally, the addresses are assigned automatically, but you can modify if needed. Generally, when referencing a Profibus slave device, you would want the PIW and PQW addresses the same because of limitations in the FBs/FCs used to read from/write to the slave.
The addresses defined for the module or slave are the PIW and PQW addresses used to access the channels on the card.
Each module is reported back in counts, which then is usually converted to an engineering unit value, using a linear conversion.
Normally the count range is 0 to 27648 for a 4-20ma signal or a 0-10v signal or whatever corresponds to 0 to 100% of span.