IEC 61784-3-1:2010(E) specifies a safety communication layer (services and protocol) based on CPF 1 of IEC 61784-1 and IEC 61158 Types 1 and 9. It identifies the principles for functional safety communications defined in IEC 61784-3 that are relevant for this safety communication layer. This second edition cancels and replaces the first edition published in 2007. This edition constitutes a technical revision. The main changes with respect to the previous edition are: - updates in relation with changes in IEC 61784-3; - adjustment of Figure 5; - change of sequence number from two octets to four octets in 7.2.2 to match the final protocol from the consortium; - addition of details for time synchronization in 7.2.4; - addition of information for safety response time in 9.3; - addition of information in constraints for calculation of system characteristics in 9.5.