Profinet Io Update Rate Configuration - GE PACSystems RXi User Manual

PROFINET IO Update Rate Configuration

10.6
Selecting PROFINET IO update rates is one of the primary means for adjusting performance
of the system. Consider the following when choosing an appropriate value.
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GFK-2816F
In general, for most applications, there is little benefit to configuring PROFINET IO
update rates faster than half the CPU Sweep time. Scheduling PROFINET IO update
rates faster than required by the application creates unnecessary loading on the
network, PNC, and PROFINET IO devices.
Keep in mind that transferring IO over the PROFINET IO network could take up to
one complete PROFINET update cycle time for the transfer to actually occur. Since
PROFINET IO production is asynchronous to the source of the produced data, in the
worst case the new production data could miss a PROFINET IO production cycle,
and thus must await the next cycle. Note, this means for an I/O loopback situation
where an application asserts an output and expects to see the output echoed on
another input, there are two PROFINET transfers involved, therefore it may take two
PROFINET IO production cycles (one for each data transfer).
It is possible that the RXi CPU, through application logic actions, can update output
data for a Remote IO Module faster than the usual I/O update rate of that remote I/O
module. The application logic must be careful not to update output data faster than
the scanning of the Remote IO Module (which is a function of both the PROFINET IO
Update Rate and IO-Device Scan). Otherwise, output data from the CPU may not
transfer to the Remote IO Module before being overwritten by new output data from
the application logic.
Chapter 10. PROFINET IO-Controller Operation
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