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

A master unit for use in a field bus network system having a ring topology, the system including the master unit and a plurality of slave units, the master unit comprising:

• a unit adapted to transmit a data message to a slave unit intended to receive the data message, which has a first counter device and a second counter device, a count of the first counter device being used to display a number of required relay steps via interposed slave units in the ring topology up to the slave unit intended for receiving the data message, and a count of the second counter device being used to display a number of completed relay steps via interposed slave units in the ring topology.

A slave unit for use in a field bus network system having a ring topology, the system including a master unit and a plurality of slave units, the slave unit comprising:

• a unit adapted to receive, process, and relay a data message, which has a first counter device and a second counter device, a count of the first counter device being used to display a number of required relay steps via interposed slave units in the ring topology up to the slave unit intended for receiving the data message and a count of the second counter device being used to display a number of completed relay steps via interposed slave units in the ring topology, the processing including modification of the count of the first counter device using a predefined algorithm upon receipt of the data message and ascertainment based on the modified count of the first counter device whether it is the slave unit intended to receive the data message, the processing further including a modification of the count of the second counter device using a predefined algorithm upon receipt of the data message.