Rockwell Automation 22-COMM-D DeviceNet Adapter - Manual (Page 132)

Glossary-8
U
UCMM (UnConnected Message Manager)
UCMM provides a method to create connections between DeviceNet
devices.
Z
Zero Data
When communications are disrupted (for example, a cable is
disconnected), the adapter and drive can respond with zero data. Zero
data results in the drive receiving zero as values for command data. If the
drive was running and using the Reference from the adapter, it will stay
running but at zero Reference.