Rockwell Automation 5720 DriveLogix System - Manual (Page 130)

Publication 20D-UM002C-EN-P - November 2003
6-14 Communicating with Devices on an EtherNet/IP Link
Connected messages are unscheduled connections on EtherNet/IP.
If a MSG instruction uses a connection, you have the option to leave the
connection open (cache) or close the connection when the message is done
transmitting.
The controller has the following limits on the number of connections that you
can cache:
Communicating with another Logix-based controller
All Logix-based controllers can use MSG instructions to communicate with
each other. The following examples show how to use tags in MSG instructions
between Logix-based controllers.
The source and destination tags:
• must be controller-scoped tags.
• can be of any data type, except for AXIS, MESSAGE, or
MOTION_GROUP.
If you: Then:
Cache the connection The connection stays open after the MSG instruction is done.
This optimizes execution time. Opening a connection each time
the message executes increases execution time.
Do not cache the
connection The connection closes after the MSG instruction is done. This
frees up that connection for other uses.
If you have this software
and firmware revision: Then you can cache:
11.x or earlier
• block transfer messages for up to 16 connections
• other types of messages for up to 16 connections
12.x or later up to 32 connections
Type of MSG Instruction: Example Source and Destination:
Logix-based controller writes to
Logix-based controller
(CIP Data Table Write)
source tag
destination tag
array_1
array_2
Logix-based controller reads from
Logix-based controller
(CIP Data Table Read)
source tag
destination tag
array_1
array_2