What is SoE in EtherCAT?

SoE is the abbreviation for Servodrive over EtherCAT. This is a protocol defined in IEC 61800-7-304 (not to be confused with the more frequently used CiA 402 standard for drives, which is defined in IEC 61800-7-201 and IEC 61800-7-301 (PDOs)).

This protocol uses IDNs instead of indexes and subindexes to read and write data to and from the drive. IDNs are similar to SDOs in CANopen, but they are optimized for drives and motion control applications.

Source: EtherLab Ethercat master, v1.6 documentation, section 6.4