Method for operating a field bus network system with ring topology and corresponding field bus network system

The method involves sending a data message through a master unit (ECU) to a slave unit among slave units (SE10, SE20, SE30, SE40), where the slave unit is appropriate for receiving the data message. The slave unit is comprised of a counter unit and a passing counter. Counter readings of the counter unit and the passing counter are modified with preset algorithms, respectively by the slave units when the data message is received. A determination is made whether the slave units are the slave unit assigned to receive the data message.