A microcontroller which can be coupled to an execution unit. For the operation of the microcontroller, a program in the microcontroller generates a message as a function of input data and transmits said message to the execution unit. For the operation of the microcontroller, accompanying the message, a check code is generated as a function of the execution of the program and is transmitted to the execution unit. For the operation of the execution unit, a test determines whether the check code is logically predefined and/or received within a predetermined time interval, wherein in the case of a positive test result, the message is designated as valid, and in the case of a negative result, the message is designated as invalid.