Publication 1756-UM050A-EN-P - December 2001
About the 1756-ENBT Module 1-3
Rack optimized connections reduce the total number of connections
needed to transfer data when using many I/O modules in a system.
The following example illustrates the benefit of rack optimized
connections.
Assume you have set up a system that contains 10 discrete I/O
modules in a remote ControlLogix chassis. If you use direct
connections to transfer data to each of the these I/O modules, you
need 10 connections to transfer all of the data, one to each of the ten
I/O modules. If you use a rack-optimized connection to transfer the
data, you only need a single connection – the connection to the
1756-ENBT module.
See the EtherNet/IP Performance and Application Guide, publication
number ENET-AP001, for more information on connections.
Mixing Rack Optimized and Direct Connections
You can mix communication formats for different I/O modules in the
same chassis. I/O modules set up to use Rack Optimization will
communicate at the rate of the RPI (requested packet interval)
configured for the 1756-ENBT module. I/O modules configured for
direct communication will communicate at their set RPI and ignore the
1756-ENBT module’s RPI.
IMPORTANT
Although rack optimized connections offer an
efficient way to use resources, there are a few
limitations on their use:
• You can only use rack optimized connections to
send data to and from discrete digital I/O
modules. Analog I/O requires direct connections.
• Rack optimized connections can contain I/O data
and status information only. Additional module
information, such as diagnostics, is not available
through a rack-optimized connection.
• All data is sent at the same time at the RPI rate of
the 1756-ENBT module.
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