Publication 1734-UM011D-EN-P - May 2011
About the Adapter 7
Support of Rack-optimized
and Direct Connections
The 1734-AENT adapter supports both direct and rack-optimized
connections. A direct connection is a real-time data transfer link between the
controller and whatever module occupies the slot that the configuration data
references. Direct connection messaging occurs at a cyclic rate specified by the
RPI during configuration. A rack-optimized connection is a grouping of data
from more than one I/O module into a single block of data sent over a single
connection at the same data rate.
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 set up a system that contains 8 digital I/O modules interfaced to a
1734-AENT adapter. If you use direct connections to transfer data to each of
the these I/O modules, you need 8 connections to transfer all of the data, one
to each of the 8 I/O modules. If you use a rack-optimized connection to
transfer the data, you only need a single connection – the connection to the
1734-AENT 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
1734-AENT adapter. I/O modules configured for direct communication
communicate at their own set RPIs and ignore the 1734-AENT adapter’s 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 1734-AENT adapter.
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