IEC 61784-3-13:2016 specifies a safety communication layer (services and protocol) based on CPF 13 of IEC 61784-2 and IEC 61158 Type 13. It identifies the principles for functional safety communications defined in IEC 61784-3 that are relevant for this safety communication layer. This safety communication layer is intended for implementation in safety devices only. This second edition cancels and replaces the first edition published in 2010. This edition constitutes a technical revision. The main changes with respect to the previous edition are listed below: - change of trade name to openSAFETY; - addition of Slim Safety PDU; - addition of SOD CRC; - addition of SSDO block transfer services; - addition of connection valid bit to SPDO; - addition of number of retries for reset guarding; - addition of user parameters that are writeable at any time; - corrections and editorial improvements.