Rockwell Automation 1756-SPESMNRMXT GuardLogix Controllers User Manual - Manuel (Page 64)

64 Rockwell Automation Publication 1756-UM020I-EN-P - August 2012
Chapter 4 Communicate over Networks
Connections over the ControlNet Network
The number of connections the controller uses is determined by how you
configure the controller to communicate with other devices in the system.
Connections are allocations of resources that provide more reliable
communication between devices compared to unconnected messages.
ControlNet connections can be scheduled or unscheduled.
The 1756-CNB and 1756-CNBR communication modules support 64 CIP
connections over a ControlNet network. However, we recommend that you
configure no more than 48 connections to maintain optimal performance.
The 1756-CN2 module supports 128 CIP connections over the ControlNet
network.
ControlNet Communication Example
This example illustrates the following:
• GuardLogix controllers can produce and consume standard or safety tags
between each other.
• GuardLogix controllers can initiate MSG instructions that send/receive
standard data or configure devices.
(1)
• The 1756-CN2 module can be used as a bridge, letting the GuardLogix
controller produce and consume standard and safety data to and from I/O
devices.
• The personal computer can upload/download projects to the controllers.
• The personal computer can configure devices on the ControlNet network,
and it can configure the network itself.
Table 16 - ControlNet Connections
Connection Type Description
Scheduled
(unique to the ControlNet network) A scheduled connection is unique to ControlNet communication. A scheduled connection lets you send and receive data repeatedly at a
predetermined interval, which is the requested packet interval (RPI). For example, a connection to an I/O module is a scheduled connection
because you repeatedly receive data from the module at a specified interval. Other scheduled connections include connections to the
following:
• Communication devices
• Produced/consumed tags
On a ControlNet network, you must use RSNetWorx for ControlNet software to enable scheduled connections and establish a network update
time (NUT). Scheduling a connection reserves network bandwidth to specifically handle the connection.
Unscheduled An unscheduled connection is a message transfer between controllers that is triggered by the requested packet interval (RPI) or the program
(such as a MSG instruction). Unscheduled messaging lets you send and receive data when needed.
Unscheduled connections use the remainder of network bandwidth after scheduled connections are allocated.
Safety produced/consumed connections are unscheduled.
(1) GuardLogix controllers do not support MSG instructions for safety data.