Data processing circuit apparatus having a data transmission unit of redundant design

Method for connecting a circuit core module to at least one external circuit module, having the following steps:

• a) providing a controller processor unit;
• b) driving the circuit core module by means of control data which are supplied by the controller processor unit via a control bus;
• c) addressing the circuit core module by means of addressing data which are supplied by the controller processor unit via an address bus;
• and
• d) transmitting data between the circuit core module and the at least one external circuit module by means of a data transmission unit,
• wherein provision is made of at least one further data transmission unit that is of redundant design with respect to the data transmission unit, a data stream being changed over between the circuit core module and the data transmission units of multiply redundant design by means of a first changeover unit and a data stream being changed over between the data transmission units of multiply redundant design and the at least one external circuit module by means of a second changeover unit, wherein the first changeover unit is changed over by means of a first test mode signal and the second changeover unit is changed over by means of a second test mode signal.