Rockwell Automation 1203-EN1 EtherNet/IP-to-SCANport Module - Manual (Page 177)

Glossary G-9
Z
Zero Data
When communications are disrupted (for example, a cable is
disconnected), the module and drive can respond with zero data. Zero
data results in the drive receiving zero as values for Logic Command,
Reference, and Datalink data. If the drive was running and using the
Reference from the module, it will stay running but at zero Reference.