Rockwell Automation 1794-L34 FlexLogix Controller System User Manual - Manual (Page 47)

Publication 1794-UM001G-EN-P - January 2007
Manage Controller Communications 47
Send and Receive
Messages Messages transfer data to other devices, such as other controllers or
operator interfaces. Messages use unscheduled connections to send or
receive data. Connected messages can leave the connection open
(cache) or close the connection when the message is done
transmitting.
Connected messages are unscheduled connections on both
ControlNet and EtherNet/IP networks.
Each message uses one connection, regardless of how many devices
are in the message path. You can programmatically change the target
of a MSG instruction to optimize message transfer time.
Determine whether to cache message connections
When you configure a MSG instruction, you have the option of
whether or not to cache the connection.
See:
• Logix5000 Controllers Common
Procedures Manual, 1756-PM001
• Logix5000 Controllers Design
Considerations Reference Manual,
This message type: With this
communication
method: Is a connected
message: The message
can be cached:
CIP data table read or write 3 3
PLC2, PLC3, PLC5, or SLC
(all types) CIP
CIP with Source ID
DH+ 3 3
CIP generic
your option
(1)
(1)
You can connect CIP generic messages. But for most applications we recommend you
leave CIP generic messages unconnected.
3
(2)
(2) Consider caching only if the target module requires a connection.
block-transfer read or write 3 3
If the message executes Then
repeatedly Cache the connection.
This keeps the connection open and optimizes execution time. Opening a connection each
time the message executes increases execution time.
infrequently Do not cache the connection.
This closes the connection upon completion of the message, which frees up that
connection for other uses.