Automatically assigning IO Addresses - References - SIMATIC AX - AX Hardware Engineering documentation - Hardware Engineering,

When a module's address is not set in the hardware declaration file, an address is automatically assigned when apax hwc compile is executed. The auto-generated addresses are persisted in the IO Address Lock File.

If a module is already present in the IO address lock file from a previous run, the same address will be assigned to the module. An already set address will be persisted even if the HWL file no longer contains it. UserDefined addresses in the HWL file that conflict with an AutoAssigned address in the lock file will cause a compile error. For the locked addresses to be reinitialized, the lock file needs to be deleted.