Hello Marcin,
Rychło w czas. There are new features coming for OH 3.x and 4.1.x fatek binding, which bring support for data registers.
Docs for version with support only for discrete inputs is here: Fatek / Facom :: ConnectorIO® Documentation, configuration remains similar for updated PR. You can look at the .adoc files which are part of pull requests. Briefly speaking there are two more channel types - data16 and data32 where you configure register (D, R etc.) and index. For 32 registers there is floating switch which cause read/written value to be treated as a floating point number. Both register kinds accept unsigned flag. At present there is no support for color and rollershuter items or two register switches known from fatek1 binding. If you need them please report issue Issues · ConnectorIO/connectorio-addons · GitHub with b-fatek label on it.
For picking up snapshot please follow this instruction: Installation and upgrade within openHAB® :: ConnectorIO® Documentation. You need to look for 3.0.0-pr72-SNAPSHOT or 4.1.0-pr-73-SNAPSHOT, depending on OH version you aim.