The process control unit is configured to execute a plurality of control processes, wherein a first control process executed on the process control unit is configured such that there is no provision for direct exchange of process variables with a second control process, but rather this exchange takes place via an interposed association module. An association specification is used to ascertain the control process(es) to which the process variable needs to be handed over. One advantage includes the increased flexibility in the exchange of process variables, which now takes place in the individual control processes by an association module. Restarts of the process control unit and associated production losses advantageously become unnecessary. Additional resources in the process control unit or in an engineering system may be reduced or avoided. The decreased complexity means that the control systems and engineering systems are developed more easily and hence also more quickly.