Rockwell Automation 1768-L45S Compact GuardLogix Controllers - Manual (Page 49)

Rockwell Automation Publication 1768-UM002C-EN-P - April 2012 49
Communicate over Networks Chapter 4
ControlNet connections can be scheduled or unscheduled.
The 1768-CNB communication modules support 64 CIP connections over a
ControlNet network.
ControlNet Communication Example
This example illustrates the following:
• Compact GuardLogix controllers can produce and consume standard or
safety tags between each other.
• Compact GuardLogix controllers can initiate MSG instructions that
send/receive standard data or configure devices.
(1)
• The 1768-CNB module can be used as a bridge, letting the Compact
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 7 - 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) Compact GuardLogix controllers do not support MSG instructions for safety data.