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OK, this is the procedure. first you need to look for GSD file of IO module type that you want to insert, then you need to go control builder F, then go hardware structure, then you need to configure Ac800f, and then module profibus master, then you add one slave using GSD option. (here there are two options GSD or FDT-dtm) with fdt-dtm is valid only if you have licence for it, the basic option is GSD that does not need any aditional license.
With FDT option configurations is easy you only need to add the modules, and all configuration is ready.
With gsd file you need to configure each module in manual way.
if you select gsd option, you should Select the file type GSD, and system add the modules type, then you can begin to add modules like you have really connected in hardware in the same order.
now you need to go to each type of module and configure IO data, you select one module and the IO is at begin is empty, with right click select new and add the type of data that is according with memory map of module you are connecting, memory map is one document that also is necesary in order to configure one module.
There are some templates that can help, because in this case, all configuration is ready. you can also find it in abb webpage
Inserting IO modules is very well explained in above answers as well as you can check in CBF help file or online help video's. Regarding configuring each and every channel no need to start from scratch for each and every byte, you can import S700 I/O templates via import , in latest version S700 i/o templates available in freelance directory in export folder @ C:\Program Files\ABB Industrial IT\Freelance\export\S700_Template_US.hwm
For S800 I/O templates check associated app here( there is procedure how to import).
FYI there are function blocks also available in same export folder.