Bridging Unscheduled Data - Allen-Bradley ControlLogix User Manual

ControlNet Communication Basics 1-3

Bridging Unscheduled Data

Unscheduled messaging is data transfer or communication between
controllers that is triggered by the program (i.e., the message instruction)
and uses one or more of the communication protocols, including
ControlNet. Unscheduled messaging allow you to send and receive data
when needed.
ControlLogix bridges transfer unscheduled data from one network protocol
(ControlNet, DeviceNet, Ethernet) to the ControlLogix backplane and vise
versa. The 1756-CNB module bridges unscheduled data, such as messaging
and programming information, between its ControlLogix backplane and the
ControlNet network.
Side of Module
Backplane = 1
ControlNet "wire" = 2
1 ss
Redundant media connector
(1756-CNBR module only)
2 nn
To properly route the messages that it receives, the 1756-CNB must be
supplied with the correct path information.To route an unscheduled
message through the ControlLogix backplane, a path segment of "1 ss" is
first required, where ss is the slot number of the module the message is
being sent to. To route the message through the ControlNet network, a path
segment of "2 nn" is required, where nn is the node number of the module
the message is being sent to.
For example, to route an unscheduled message through a 1756-CNB
module in chassis slot 3 through another 1756-CNB module at ControlNet
node 6 in a different chassis, the path would be:
1, 3, 2, 6, . .
to backplane to ControlNet node 6
to backplane slot 3
onto ControlNet wire
The next device in the path could be a controller, an I/O device, a bridge to
another communication protocol such as DeviceNet, etc.
1756-6.5.3 - December 1999