This part of IEC 61131 specifies a single-drop digital communication interface technology for small sensors and actuators SDCI (commonly known as IO-LinkTM2), which extends the traditional digital input and digital output interfaces as defined in IEC 61131-2 towards a point-to-point communication link. This technology enables the transfer of parameters to Devices and the delivery of diagnostic information from the Devices to the automation system. This technology is mainly intended for use with simple sensors and actuators in factory automation, which include small and cost-effective microcontrollers. This part specifies the SDCI communication services and protocol (physical layer, data link layer and application layer in accordance with the ISO/OSI reference model) for both SDCI Masters and Devices. This part also includes EMC test requirements. This part does not cover communication interfaces or systems incorporating multiple point or multiple drop linkages, or integration of SDCI into higher level systems such as fieldbuses.