A module unit for connecting a data bus participant to a local bus. The module unit has a first input interface and a first output interface which can be connected to the local bus, a first data connection interface which can be connected to the data bus participant, and a first switch which is adapted so as to assume a first or a second switch state depending on a control input from the data bus participant, connect the first input interface to the first output interface in the first switch state, and connect the first data connection interface to the first output interface in the second switch state.