Rockwell Automation Publication 1756-UM058G-EN-P - November 2012 49
Common Module Features Chapter 3
Mixing CST and CIP Sync Modules in a ControlLogix System
CST is automatically enabled for each chassis that has been configured to use
CIP Sync. Therefore, it is possible to include modules that use CST for their time
base into systems that have been configured to use CIP Sync. Also, there is a
direct correlation between CIP Sync system time and the local chassis CST time.
The CIP Sync system time and local chassis CST time are related by this
equation:
CIP Sync system time = CST time + offset
The offset in the above equation is a value unique to each chassis and can be
obtained by using one of these methods:
• CSTOffset from the Wall Clock Time (WCT) object of a controller in
the chassis
• SystemOffset from the Time Synchronize object of a controller in the
chassis
• LocalClockOffset returned in an I/O connection from a CIP Sync capable
module in the chassis
The relationship described above enables CST and CIP Sync-based I/O to
interoperate as long as the offset in the chassis containing the CST-based module
is accessible.
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