Rockwell Automation 1756-SYNCH ControlLogix SynchLink Module User Manual - Manual (Page 24)

Publication 1756-UM521C-EN-P - July 2004
2-4 Time Synchronization in the ControlLogix System
System Synchronization
When a SynchLink system is initialized, the individual SynchLink
nodes power-up at separate times and the individual SynchLink node
clocks begin to count at arbitrary points in time. When this occurs, the
system is not yet synchronized. As the master node clock counts, it
reaches a point where it rolls over and goes back to zero.
When the rollover occurs, the SynchLink Time Master transmits a
beacon signal to the SynchLink Time Slaves; the beacon is included in
the control field of the transmitted message. When the SynchLink
Time Slave receives the first message with the beacon signal, it begins
to adjust the 1μs time base of its node clock to synchronize with the
master clock. This process can be gradual or immediate, depending
on the product implementation.
Figure 2.2
After a SynchLink Time Slave is synchronized with the Time Master,
each SynchLink frame that is transmitted serves as a 50μS “tick” (or
mark) used for the periodic adjustment of its clock’s 1μS time base.
This process provides highly accurate results.
Figure 2.3
Master
Slave
Beacon Beacon Beacon
Time adjustment
Initial Start-Up
42982
Master
Slave
Synchronized Operation
42983
Beacon signal
synchronizes
SynchLink node
clocks
42984
SynchLink 50 microsecond message frame
serves as a “tick” to keep clocks synchronized