This part 2 of IEC 61139 specifies the extensions to SDCI in IEC 61131-9: for functional safety. This comprises: " a standardized OSSDe interface for redundant switching signals based on IEC 61131-2, " minor modifications/extensions to state machines of SDCI to support the safety operations, " a lean functional safety communication protocol on top of the standard SDCI communication which is a black channel according to IEC 61784-3:2021, " protocol management functions for configuration, parameterization, and commissioning, " IODD extensions for functional safety, " a Device tool interface to support Dedicated Tools according to functional safety standards. This part 2 does not cover: " communication interfaces or systems including multi-point or multi-drop linkages, " communication interfaces or systems including multi-channel or encrypted linkages, " wireless communication interfaces or systems, " integration of SDCI-FS into upper-level systems such as fieldbuses/FSCPs.