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PACSystems* RX3i
PROFINET Controller Manual
– December 2011
GFK-2571A
4
PROFINET IO Update Rate Configuration
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.
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 RX3i 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.
