Publication 1734-UM014A-EN-P - November 2010
About the Adapters 7
Support of Rack-optimized
and Direct Connections
The I/O adapters supports both direct and rack-optimized connections. A
direct connection is a real-time data transfer link between the controller and
the module occupying the slot that the configuration data references.
Direct I/O connections occur at a cyclic rate specified by the RPI during
configuration. A rack-optimized connection is a grouping of data from one or
more digital I/O modules into a single block of data sent over a single
connection at the same data rate.
Analog, safety, and speciality modules cannot participate in the rack-optimized
connection; these modules require a direct I/O connection.
Rack-optimized connections reduce the total number of connections needed
to transfer data when using many digital I/O modules in a system. The
following example illustrates the benefit of rack-optimized connections.
Assume you set up a system that contains eight digital I/O modules interfaced
to an adapter. If you use direct connections to transfer data to each of the
these I/O modules, you need eight connections to transfer all of the data, one
to each of the eight I/O modules. If you use a rack-optimized connection to
transfer the data, you only need a single connection – the connection to the
I/O adapter.
See the EtherNet/IP Performance and Application Guide, publication
number ENET-AP001
, for more information on connections.
Mix Rack-optimized and Direct Connections
You can mix communication formats for different I/O modules
communicating through the same adapter. I/O modules set up to use rack
optimization communicate at the rate of the RPI configured for the adapter.
I/O modules configured for direct communication communicate at their own
individual RPIs and ignore the rack-optimized RPI.
Although rack-optimized connections offer an efficient way to use
resources, there are a few limitations on their use:
• You can use only rack-optimized connections to send data to
and from digital I/O modules. Analog or speciality I/O
requires direct connections.
• All data is sent at the same time as the RPI rate of the I/O
adapters. If the update rate required for a digital module is
different from the RPI of the rack-optimized connection, a
direct connection to that digital I/O module is required.
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