Rockwell Automation 5730 DriveLogix5730 Controller for PowerFlex 700S Drives with Phase II Control - Manual (Page 150)

7-10 Communicating with Devices on a ControlNet Link
firmware, the MSG instruction errors because the destination
tag is not large enough. To correct this error, change the
destination tag to a DINT data type.
MSG instructions are unscheduled. The type of MSG determines whether or
not it requires a connection. If the MSG instruction requires a connection, it
opens the needed connection when it is executed. You can configure the
MSG instruction to keep the connection open (cache) or to close it after
sending the message.
Connected messages are unscheduled connections on ControlNet.
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:
This type of message: And this communication method: Uses a connection:
CIP data table read or write X
PLC2, PLC3, PLC5, or SLC (all types) CIP
CIP with Source ID
DH+ X
CIP generic CIP Optional
(1)
block-transfer read or write X
(1) You can connect CIP generic messages, but for most applications, we recommend you leave CIP generic messages unconnected.
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:
12.x or later up to 32 connections