This section of IEC 60870-5 applies to protection equipment with coded bit serial data transmission for exchanging information with control systems. It defines a companion standard that enables interoperability between protection equipment and devices of a control system in a substation. The defined companion standard utilizes standards of the IEC 60870-5 series. This section of IEC 60870-5 presents specifications for the informative interface of protection equipment. This standard does not necessarily apply to equipment that combines protection and control functions in the same device sharing a single communication port. This section of IEC 60870-5 describes two methods of information exchange: the first is based on explicitly specified APPLICATION SERVICE DATA UNITS (ASDUs) and application procedures for transmission of ‘standardized’ messages, and the second uses generic services for transmission of nearly all possible information. The ‘standardized’ messages do not cover all possible protection functions, and furthermore a protection device may support only a subset of the messages specified in this standard. For interoperability purposes, in specific applications, this subset has to be specified in clause 8. The use of predefined messages and application procedures is mandatory, if applicable. In other cases generic services shall be used. The ‘private ranges’ defined in this standard are maintained for compatibility reasons; however, their use is not recommended for future applications.