Specifications

1768-SG001A-EN-P -- March 2006

CompactLogix Selection Guide

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A Logix system uses a connection to establish a communication link between two

devices. Connections can be:

y Controller to local I/O modules or local communication modules

y Controller to remote I/O or remote communication modules

y Controller to remote I/O (rack-optimized) modules

y Produced and consumed tags

y Messages

You indirectly determine the number of connections the controller uses by configuring the

controller to communicate with other devices in the system.

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Unscheduled connection

• Deterministic

An unscheduled connection is a message transfer between controllers that is triggered by

the Requested Packet Interval (RPI) or the program (such as a MSG instruction).

Unscheduled messaging lets you send and receive data when needed.

All EtherNet/IP connections are unscheduled.

Unconnected message

• Least deterministic

An unconnected message is a message that does not require connection resources. An

unconnected message is sent as a single request/response.

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In a 1768 CompactLogix system, the only connections to consider are those associated

with each 1768-ENBT module in the system.

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1768-ENBT

128 Logix (CIP) connections (all connections are unscheduled)

64 TCP/IP connections

The total connection requirements for a 1768 CompactLogix system include both local

and remote (distributed) connections. Tallying local controller connections is not an issue

because the controllers supports all the connections required for the maximum number

of I/O modules and 1769-SDN scanners in one system. It is important to tally remote

(distributed) connections via the EtherNet/IP network because each 1768-ENBT scanner

supports 64 connections.