Rockwell Automation 1756-IH16ISOE ControlLogix Sequence of Events Module - Manual (Page 130)

Publication 1756-UM528A-EN-P - April 2004
C-2 Synchronizing CSTs Across Multiple Chassis
• The controller in the local chassis typically serves as the time
master for its chassis; the 1756-SYNCH module in the local
chassis can also serve as the time master.
• The 1756-SYNCH module in the local chassis sends a
common CST time reference to 1756-SYNCH modules in
remote chassis over a fiber optic connection.
• The 1756-SYNCH module in remote chassis receive the CSTs
from the 1756-SYNCH module in the local chassis and use
that time to set the CST on the backplane of the chassis where
they reside.
• All the other modules in the remote chassis operate with a
CST from the backplane that is synchronized with the CST in
the controller’s chassis.
Figure C.1
Once the CST is synchronized between chassis, as shown in
Figure C.1, the modules in chassis #2 use the same CST as the
modules in chassis #1. You can use 1756-SYNCH modules to
synchronize CSTs for up to 257 ControlLogix chassis.
Synchronization of CSTs between ControlLogix chassis provides a
common CST with no more than +/-5
µs drift between chassis.
43743
CST on
CST on backplane
synchronized with Chassis
Chassis #1 Chassis #2
CST propagated via
Controller - Sets CST
for local chassis. 1756-SYNCH - Gets CST from
backplane and sends it to the
other 1756-SYNCH modules. 1756-SYNCH - Gets CST
from 1756-SYNCH in local
chassis and sets it on the
backplane in Chassis #2 Sequence of events
module in remote chassis
timestamps input data
with the same CST as
used by the controller in
Chassis #1.
ControlNet