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Ethernet Media Redundancy Protocol
PROFINET also supports redundancy in the form of Ethernet Media Redundancy Protocol
(MRP). As shown in Figure 20, this form of redundancy is designed to permit all devices on the
network to continue to communicate even though the network cable has been compromised
at one point. For details, see the RX3i PROFINET Controller System Manual (GFK-2571).
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4.1.3 I/O Scans
As shown in Figure 7, there are a number of I/O Scans that effect how the input and output
devices on the Genius bus exchange data with the RSX3i PLC.
The RX3i scan reads input data from all the devices connected to it and active in its
configuration. It uses this input data to solve the control logic supplied for the application. At
the conclusion of the logic execution, the output data is ready for distribution and the output
portion of the RX3i scan takes place.
The PNC001 PROFINET Controller operates on its own cycle, receiving input data for all devices
connected to it, including the GCG001 Genius Gateway. It passes the input data to the RX3i
during the RX3i input scan. When the RX3i performs its output scan, the output data
configured to the PNC001 is transmitted by the PNC001 to the output devices on its network,
including the GCG001 Genius Gateway.
The GCG001 also operates on its own scan cycle. As the Genius bus token passes from one
SBA to the next, each device on the Genius Bus takes its turn to transmit its input data to the
GCG001, which then makes that input data available to the PNC001. The GCG001 also
consumes all the output data produced by the PNC001 and broadcasts that data to all the
output devices on the Genius bus whenever it receives the Genius Bus token.
All of the I/O scans described above are asynchronous and may vary depending on the path
through the RX3i logic, traffic on the PROFINET and traffic on the Genius Bus. Should I/O
update rates be a concern for the application, it would be prudent to perform a worst-case
analysis of the interacting scan cycles.
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Figure 20: PROFINET Media Redundancy
PACSystems RX3i Genius Communications Gateway User Manual
Chapter 4. System Operation
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