GE RX3i PROFINET - Data Coherency; Sampling Rate; Differences from Main (CPU) Rack

Chapter 5. Operations
54 PACSystems* RX3i PROFINET IO-Scanner User Manual GFK-2737F
5.2.2 Data Coherency
The RX3i PNS provides coherency at a submodule basis only. This means that output data from a single
I/O Controller for multiple modules in the PNS rack might not be applied by the PNS during the same
output scan. Likewise, input data from all modules read in a single PNS input scan may not be produced
by the PNS during the same PROFINET I/O cycle.
5.2.3 Sampling Rate
The PROFINET Device Update Rate should be taken into consideration with regard to I/O devices in a
Scanner rack. I/O data that changes quickly, such as status bits that represent an event in a module and
are only set for one scan of the module, may be missed if the update period spans multiple scans of the
module. In some cases, other functionality may be utilized to capture momentary events. For example,
High-Speed Counter Over Range, Under Range, Overflow, and Underflow status conditions can be latched
by configuring an unused counter to mirror the operating counter and assigning the event condition as a
strobe source. The corresponding strobe status and acknowledge bits may be used to monitor and
acknowledge the condition.
5.2.4 Differences from Main (CPU) Rack
The following CPU operations are not supported or exhibit different behavior than when used with I/O
modules in a CPU rack.
5.2.4.1 Interrupts
Interrupts are not supported for I/O modules in a PNS rack. Service Requests that disable, enable,
suspend, or resume interrupts have no effect. Interrupt driven Logic blocks cannot be used with I/O
modules in a PNS rack, and interrupt status bits should be ignored.
5.2.4.2 Do I/O and Suspend I/O
Do I/O and Suspend I/O operations are limited to updating or suspending the data between the CPU and
PNC. The PROFINET I/O scan is not altered (that is, DO_IO data is not exchanged with the PNS any faster
than the PROFINET update rate allows).