Error detection in fault secure controllers using state encoding

In applications where safety is of utmost importance, defective functions must frequently be detected very early in order to restore the system to a safe operating condition. At the same time the availability may not be restricted by measures implemented to detect errors. The efficiency of error detection state encodings for a control unit is investigated based on the example of the Motorola microprocessor core M68HC11. The terms "dependent encoding" and "independent encoding" are introduced. The designed circuits are compared with regard to error detection of stuck-at errors and chip area. The degree of error detection is shown with the help of a fault simulation.