Method for the configuration and parameterisation of fieldbus subscribers (Ctr,Dev) that are connected to one another via a fieldbus, wherein at least one first fieldbus subscriber (Dev) is designed so as to provide and/or to receive process data and a second fieldbus subscriber (Ctr) is designed in order to allow a user program to run, wherein in - a first step using a configuration tool a topology (Topo) having configuration parameters of the fieldbus subscribers (Ctr,Dev) is determined in a configuration file, and in - a second step the first fieldbus subscriber (Dev) is parameterised for later communication via the fieldbus using at least one configuration data set (Dconf) comprising at least one first part of the configuration file, in - a third step an object-oriented class (class) having elements and functions (f) for the communication between the second fieldbus subscriber (Ctr) and the first fieldbus subscriber (Dev) is generated from the configuration file and further code parts (C1,...,C5) from a program library, wherein in - a fourth step the class (class) is instantiated in the user program of the second fieldbus subscriber (Ctr) and when the user program is being executed the functions (f) are used for the communication, whereby the access to the process data is rendered possible, wherein the fieldbus subscribers (Ctr,Dev) are divided into two of the following types, an IO controller type for the second fieldbus subscriber (Ctr) and an IO device type for the first fieldbus subscriber (Dev), wherein - the IO controller type is the type of device that assumes control tasks and in which the user program is executed and - the IO device type is the type of device that receives data as a field device from an industrial process or outputs data to an industrial process, wherein said device is controlled by the devices of the IO controller type, characterised in that - using the configuration tool a mesh network topology (Masch-Topo) with the configuration parameters of the fieldbus subscribers (Ctr,Dev) is determined in a mesh configuration file (mCD), and wherein - the generation of the class (class) is divided into a generation of a server class and into a generation of a client class and in - fieldbus subscribers of the type IO controller the two classes (SC,CC) are instantiated in the user program and in the - fieldbus subscribers of the type IO device at least the server class is instantiated. - a first step using a configuration tool a topology (Topo) having configuration parameters of the fieldbus subscribers (Ctr,Dev) is determined in a configuration file, and in - a second step the first fieldbus subscriber (Dev) is parameterised for later communication via the fieldbus using at least one configuration data set (Dconf) comprising at least one first part of the configuration file, in - a third step an object-oriented class (class) having elements and functions (f) for the communication between the second fieldbus subscriber (Ctr) and the first fieldbus subscriber (Dev) is generated from the configuration file and further code parts (C1,...,C5) from a program library, wherein in - a fourth step the class (class) is instantiated in the user program of the second fieldbus subscriber (Ctr) and when the user program is being executed the functions (f) are used for the communication, whereby the access to the process data is rendered possible, wherein the fieldbus subscribers (Ctr,Dev) are divided into two of the following types, an IO controller type for the second fieldbus subscriber (Ctr) and an IO device type for the first fieldbus subscriber (Dev), wherein - the IO controller type is the type of device that assumes control tasks and in which the user program is executed and - the IO device type is the type of device that receives data as a field device from an industrial process or outputs data to an industrial process, wherein said device is controlled by the devices of the IO controller type, characterised in that - using the configuration tool a mesh network topology (Masch-Topo) with the configuration parameters of the fieldbus subscribers (Ctr,Dev) is determined in a mesh configuration file (mCD), and wherein - the generation of the class (class) is divided into a generation of a server class and into a generation of a client class and in - fieldbus subscribers of the type IO controller the two classes (SC,CC) are instantiated in the user program and in the - fieldbus subscribers of the type IO device at least the server class is instantiated. - the IO controller type is the type of device that assumes control tasks and in which the user program is executed and - the IO device type is the type of device that receives data as a field device from an industrial process or outputs data to an industrial process, wherein said device is controlled by the devices of the IO controller type, characterised in that - using the configuration tool a mesh network topology (Masch-Topo) with the configuration parameters of the fieldbus subscribers (Ctr,Dev) is determined in a mesh configuration file (mCD), and wherein - the generation of the class (class) is divided into a generation of a server class and into a generation of a client class and in - fieldbus subscribers of the type IO controller the two classes (SC,CC) are instantiated in the user program and in the - fieldbus subscribers of the type IO device at least the server class is instantiated.