The present invention describes a control system for controlling safety-critical processes. The control system has a first control unit for controlling a safety-critical process and at least one signal unit linked to the safety-critical process via I/O channels. It further comprises a field bus connecting said first control unit and said signal unit, and a bus master for controlling communication on said field bus. Said first control unit and said signal unit each comprise safety-directed arrangements for ensuring failsafe communication among each other. Said bus master is connected to said field bus separately from said first control unit and said signal unit.