Rockwell Automation Publication 1756-UM001M-EN-P - February 2012 125
Manage Controller Communication (connections) Chapter 7
The number of available connections limits the number of tags that can be
produced or consumed. If the controller uses all of its connections for I/O and
communication devices, no connections are left for produced and consumed tags.
For more information about produced/consumed tags, see the Logix5000
Controllers Produced and Consumed Tags Programming Manual, publication
1756-PM011
.
Send and Receive Messages
Messages transfer data to other devices, such as other controllers or operator
interfaces. The MSG instruction is a ladder logic output instruction that
asynchronously reads or writes a block of data to or from another module over
the backplane or a network. The size of the instruction depends on the data types
and message command programmed by the user.
Messages use unscheduled connections to send or receive data. These connected
messages can leave the connection open (cache) or closed when the message is
done transmitting.
Table 33 - ControlLogix Modules and Available Connections
Module Type Cat. No. Available Connections
Controller 1756-L7x 500
1756-L6x 250
EtherNet/IP • 1756-EN2F
• 1756-EN2T
• 1756-EN2TXT
• 1756-EN2TR
256
• 1756-ENBT
• 1756-EWEB
128
ControlNet • 1756-CN2
• 1756-CN2R
• 1756-CN2RXT
128
• 1756-CNB
• 1756-CNBR
64
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