Inputs are periodic or by exception based on the signal configuration and outputs are sent when they are written at a rate limited by the execution rate of the module that is writing the outputs.
IEC 61850 defines specific names to identify data. Data is contained in Intelligent Electronic Devices within logical devices and logical nodes. The logical devices and signals defined under the IEC 61850 Intelligent Electronic Devices include the information needed to identify which data element within a logical node of a logical device is to be accessed.