I/O Scans; Figure 23: Profinet Media Redundancy - GE GFK-2892F User Manual

Chapter 4. System Operation
Ethernet Media Redundancy Protocol
PROFINET also supports redundancy in the form of Ethernet Media Redundancy Protocol (MRP). As shown in
Figure 23, 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, refer to the
PACSystems RX3i & RSTi-EP PROFINET I/O Controller Manual, GFK-2571.

Figure 23: PROFINET Media Redundancy

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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