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Manage Controller Communications
Send and Receive
Messages
47
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.
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:
3
3
3
3
CIP generic
your option (1)
3(2)
block-transfer read or write
3
3
CIP data table read or write
PLC2, PLC3, PLC5, or SLC
(all types)
CIP
CIP with Source ID
DH+
(1)
You can connect CIP generic messages. But for most applications we recommend you
leave CIP generic messages unconnected.
(2)
Consider caching only if the target module requires a connection.
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.
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.
Publication 1794-UM001G-EN-P - January 2007