Rockwell Automation Publication 1769-UM011H-EN-P - April 2012 77
Manage Controller Communication Chapter 5
Determine Whether to Cache Message Connections
When you configure a MSG instruction, you can cache or not cache the
connection.
Connections
A Logix5000 system uses a connection to establish a communication link
between two devices. Connections can be:
• a controller to local I/O modules or local communication modules.
• a controller to remote I/O or remote communication modules.
• a controller to remote I/O (rack-optimized) modules.
• produced and consumed tags.
• messages.
• controller access by RSLogix 5000 programming software.
• controller access by RSLinx software for HMI or other applications.
The limit of connections may ultimately reside in the communication module
you use for the connection. If a message path routes through a communication
module, the connection related to the message also counts towards the
connection limit of that communication module.
Table 13 - Caching Messages
Message Execution Function
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, freeing up that connection for other uses.
Table 14 - Connections Overview
Device Supported Connections
CompactLogix controller (1769-L31)
100
Built-in ControlNet communication port (1769-L32C and 1769-
L35CR controllers only)
Built-in EtherNet/IP communication port (1769-L32E and
1769-L35E controllers only)
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