Publication 20D-UM002C-EN-P - November 2003
What Is DriveLogix? 2-9
How the DriveLogix System
Uses Connections
The DriveLogix system uses a connection to establish a communication link
between two devices. The DriveLogix system has enough internal resources to
support a connection to every local I/O module and 32 connections through
the daughtercard (e.g. the 1788-ENBT card). However, the daughtercard’s
connection limit is the limiting factor when sizing a system.
Connections can be:
• controller to local I/O modules or local communication cards
• controller to remote I/O or remote communication modules
• controller to remote I/O (rack optimized) modules
• produced and consumed tags
• messages
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
communications between devices than unconnected messages. The
DriveLogix system supports both scheduled and unscheduled connections and
unconnected messages.
Method: Description:
scheduled connection
• most deterministic
• unique to ControlNet
A scheduled connection is unique to ControlNet communications. A scheduled connection
lets you send and receive data repeatedly at a predetermined rate, 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 rate. 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).
unscheduled connection
• deterministic
• used by both ControlNet and
EtherNet/IP
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.
All EtherNet/IP connections are unscheduled.
unconnected message
• least deterministic
An unconnected message is a message that does not require connection resources . An
unconnected message is sent as a single request/response.
