Profinet Io Update Rate Configuration; Pacsystems Cpu Operations For Profinet; Reference Id Variables For The Pacsystems Application - Emerson PACSystems RX3i User Manual

RSTI-EP PROFINET I/O Controller User Manual
GFK-2571R
When designing a PROFINET IO system, consider and weigh these factors appropriately to
achieve an optimal IO system for the application.
4.6

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,
PROFINET Controller, 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 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 PACSystems 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.
4.7

PACSystems CPU Operations for PROFINET

This section describes several PACSystems CPU functions as related to their operation when
used with a PROFINET network.
In addition, PACSystems CPUs with version 7.0 or later firmware and PAC Machine Edition
version 7.0 or later provide special tools for use in systems with PROFINET networks based
on the PROFINET Controller:
• Reference ID Variables (RIVs)
• PNIO_DEV_COMM function block
4.7.1 Reference ID Variables for the PACSystems
Application
RIVs are available to the PACSystems application logic to provide a simple symbolic
reference to an entity. The following RIV types are defined for use with PROFINET Controllers
and IO Devices.
PROFINET System Operation
Section 4
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