Data Coherency; Performance Factors - Emerson PACSystems RX3i User Manual

RSTI-EP PROFINET I/O Controller User Manual
GFK-2571R
• PROFINET IO-Device
node as quickly as possible. The PNS stores the input data gathered from each of the
input modules in that node into its internal memory. On each output scan, the PNS
writes the output data from its internal memory to the output modules in its node.
• PROFINET IO Production
Device publishes data from its internal memory onto the network at each scheduled
PROFINET production cycle (note: production cycles between IO Controllers and IO
Devices are not synchronized, each publishes at its configured update rate
independently). The PROFINET Controller publishes output data received from the CPU
to each IO Device, and the IO Device publishes input data from its memory to the
PROFINET Controller.
• PACSystems CPU
an output scan. The CPU input scan retrieves the current input data being stored within
the PROFINET Controller. This input data is then available for use by the application
logic. After the logic solution, the CPU output scan writes the outputs to the PROFINET
Controller.
4.4

Data Coherency

In a PACSystems PROFINET network, it is important to note that I/O data coherency is at the
PROFINET submodule level. The PROFINET Controller 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 PROFINET Controller may not be consumed during a single CPU
input scan.
4.5

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
PROFINET System Operation
Scan: in Figure 91, each VersaMax PNS scans all the modules in its
3rd party devices: The conveyance of I/O data between an I/O module and the
PROFINET IO network is device dependent. Third party manufacturer documentation
should be referred to for specifics for a device.
Cycle: each PROFINET Controller in a CPU node and each IO
Sweep: the PACSystems CPU Sweep includes both an input scan and
Section 4
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