This question has come up in the Community before and I do not know if there was ever a solution presented for EtherNet/IP Unconnected Explicit Messaging. If you are willing to do some testing and offer feedback as to the results, I can try to help you through the process. I do not have, nor am I familiar with, the PowerFlex 525, but I dabble with EtherNet/IP a bit. So, I can only base my information on the vendor's documentation.

Before Testing:

• Configuration of the following parameters let you determine the action of the embedded EtherNet/IP adapter and drive if the I/O communication is disrupted, the controller is idle, or Explicit Messaging for the drive is disrupted.
  • C143 (EN Communication Fault Action)
  • C144 (EN Idle Fault Action)
• Apply power to the drive AFTER connecting the EtherNet/IP adapter to the network.
• Set parameter P046 (Start Source 1) to 5 "EtherNet/IP".
• Set parameter P047 (Speed Reference 1) to 15 "EtherNet/IP".

Before testing the Do-more EIPMSG instructions with the EtherNet/IP adapter, be sure to provide a variable for the General Status fields, as well as a reference to an 8 element UINT Array for the Extended Status (make a memory block). This will help in diagnosing issues while troubleshooting.  

Note: EtherNet/IP Explicit Messaging uses TCP port 44818.

Testing:

Set Control Timeout value using the following information in an EIPMSG instruction:

• Class: 4 (0x04)
• Instance: 0 (0x00)
• Attribute: 100 (0x64)
• Service: 16 (0x10) Set_Attribute_Single
• Size: 2 bytes (UINT)
• Description: Control timeout in seconds

Read Drive Status information from the Input Data Assembly:

• Class: 4 (0x04)
• Instance: 1 (0x01)
• Attribute: 3 (0x03)
• Service: 14 (0x0E) Get_Attribute_Single
• Size: 4 bytes
• Description: 
  • Word 0: Logic Status
  • Word 1: Speed Feedback

Write Drive Commands to the Output Data Assembly:

• Class: 4 (0x04)
• Instance: 2 (0x01)
• Attribute: 3 (0x03)
• Service: 16 (0x10) Set_Attribute_Single
• Size: 4 bytes
• Description: 
  • Word 0: Logic Command
  • Word 1: Speed Reference

Definitions for Logic Command Word and Logic Status Word can be found on pages 153 and 154 of the link below:

https://literature.rockwellautomation.com/idc/groups/literature/documents/um/520com-um001_-en-e.pdf#page=153

Let me know if this gets you moving forward OR if we need to test new values within the instructions.