52 Rockwell Automation Publication 1769-UM011H-EN-P - April 2012
Chapter 4 Communicate over Networks
Figure 5 - CompactLogix ControlNet Overview
Connections over ControlNet
You indirectly determine the number of connections the controller uses by
configuring 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 Network
Distributed I/O
1756-CNB Module (as an
adapter) with 1756 I/O
Modules
1794-ACN15 Adapter with
1794 I/O Modules
Personal Computer/Workstation
CompactLogix Controller
FlexLogix Controller with
1788-CNC Card
1734-ACNR Adapter with
1734 I/O Modules
PowerFlex 700S Drive
PanelView Terminal
PLC-5/40C15 Controller
Table 7 - ControlNet Connection Methods
Connection Method Description
Scheduled A scheduled connection is unique to ControlNet communication. A scheduled connection lets you send and receive data repeatedly at a set 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:
• communication devices.
• produced/consumed tags.
On a ControlNet network, you must use RSNetWorx for ControlNet to enable all 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 nodes that is triggered by ladder logic or the program (such as a MSG instruction).
Unscheduled messaging lets you send and receive data when needed. Unscheduled messages use the remainder of network bandwidth after
scheduled connections are allocated.
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