Allen-Bradley 1756-L63XT, User Manual

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Rockwell Automation Publication 1756-UM001O-EN-P - October 2014 89
Communication Networks Chapter 5
support it. If non-DDR modules are also in the chassis, communication between
those modules is at the non-DDR rate.
For example, you can have a chassis with two 1756-L7 x controllers in slots 0 and
1 communicating with each other by using DDR, and two 1756-L6 x controllers
in slots 2 and 3 communicating by using non-DDR.
When multicast communication is used within a chassis to multiple modules, the
transmission rate is limited to the slowest module—or at the non-DDR rate.
For example, if a 1756-L7 x controller is producing a tag to a 1756-L7 x controller
and a 1756-L6 x controller on the same multicast connection, it must use the
non-DDR rate.
ControlNet Network
Communication The ControlNet network is a real-time control network that provides high-speed
transport of time-critical I/O and interlocking data and messaging data. This
includes the upload and download of program and configuration data on one
physical-media link. The highly efficient data transfer capability of the
ControlNet network significantly enhances I/O performance and peer-to-peer
communication in any system or application.
The ControlNet network is highly deterministic and repeatable and is unaffected
when devices are connected or disconnected from the network. This quality
results in dependable, synchronized, and coordinated real-time performance.
The ControlNet network often functions as the following:
• A substitute/replacement for the remote I/O (RIO) network because the
ControlNet network adeptly handles large numbers of I/O points
• A backbone for multiple distributed DeviceNet networks
• A peer interlocking network