GFK-2571A Chapter 4 System Operation 4-9
Data Coherency
In a PACSystems RX3i PROFINET network, it is important to note that I/O data coherency is at the
PROFINET submodule level. The RX3i PNC coherently transfers I/O data to and from the CPU on a
PROFINET submodule basis. This means that output data from a single CPU output scan for
multiple PROFINET submodules may not be transferred during the same PROFINET IO production
cycle. Conversely, input data consumed from a single PROFINET IO cycle by the PNC may not be
consumed during a single CPU input scan.
Performance Factors
There are many factors that affect the timing of I/O as it flows through the system. Primary factors
include:
CPU Sweep Time
Configured PROFINET IO Update Rate(s)
Number of PROFINET IO Devices
Number of IO modules
Network latency and loading (for example, switching hardware, additional non-PROFINET
network traffic)
I/O Module Filter Times
When designing a PROFINET IO system, consider and weigh these factors appropriately to achieve
an optimal IO system for the application.
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