Rockwell Automation Publication 1756-UM001M-EN-P - February 2012 95
Communication Networks Chapter 5
Double Data Rate (DDR) Backplane Communication
DDR communication can be achieved with the 1756-L7x controller. These
communication modules support DDR when used in conjunction with the
1756-L7x controller:
• 1756-EN2T/C
• 1756-EN2TR/B
• 1756-EN2TF/B
• 1756-EN2TXT/C
• 1756-EN3TR/A
• 1756-RM/B
DDR communication is achieved most efficiently when all modules in the
communication path are DDR modules, or, in other words, as a single
conversation (connection) only between DDR modules.
DDR communication is achievable in a chassis with a mix of DDR and non-
DDR modules. The DDR communication occurs between the modules that
support it. If non-DDR modules are also in the chassis, communication between
those modules will be at the non-DDR rate.
For example, you could have a chassis with two 1756-L7x controllers in slots 0
and 1 communicating with each other using DDR, and two 1756-L6x controllers
in slots 2 and 3 communicating 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-L7x controller is producing a tag to a 1756-L7x controller
and a 1756-L6x 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 both time-critical I/O and interlocking data and messaging data.
This includes uploading and downloading of program and configuration data on
a single physical-media link. The ControlNet network’s highly-efficient data
transfer capability 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.
To Next Page
Loading...
Need help?
General
