50 Rockwell Automation Publication ENET-UM004B-EN-P - November 2015
Chapter 4 Add an EtherNet/IP Communication Module to a Controller Project
Time Synchronization
In certain situations, the I/O modules can synchronize with the adapter before
the adapter synchronizes with the system Grandmaster clock. This
synchronization occurrence leads to a time difference between the I/O and the
Grandmaster clock until the adapter synchronizes with the Grandmaster clock.
In your logic, verify that the adapter is synchronized with the Grandmaster clock
(CIPSyncValid) before you initiate timestamp requests or scheduled outputs
from your I/O modules. A system with intermediate devices, such as network
bridges and switches, can require that you insert a delay until the time stabilizes in
the system.
For information on how to verify that the adapter is synchronized to a
Grandmaster clock, see CIP Sync Diagnostics in the Integrated Architecture and
CIP Sync Configuration Application Technique, publication
IA-AT003. This
publication also includes information on Time Sync Object Attributes.
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