Real Time Class Communication - Datalogic AMT58*-PN Series Instruction Manual

AMT58x-PN ProfiNET®

11. Real time class communication

Within PROFINET IO, process data and alarms are always
transmitted in real time. Real-Time for PROFINET (RT) is based on
the definitions of IEEE and IEC for high-performance data exchange
of I/O data. RT communication constitutes the basis for data
exchange in PROFINET IO.
Real-time data are handled with higher priority compared to
TCP(UDP)/IP data. This method of data exchange allows bus cycle
times in the range of a few hundred milliseconds to be achieved.
Isochronous data exchange with PROFINET is defined in the
Isochronous-Real-Time (IRT) concept. IRT communication is always
clock synchronized and only possible within an IRT domain.
Isochronous realtime communication differs from realtime
communication mainly in its isochronous behavior: the start of a bus
cycle can deviate by a maximum of 1 µs (jitter is less then 1 µs). IRT
is required in motion control applications (positioning operations), for
example. This communication is required, for example, for high-
accuracy closed-loop control tasks.
11.1 Real-time classes in PROFINET IO
To enable enhanced scaling of communication options and, thus,
also of determinism in PROFINET IO, real-time classes have been
defined for data exchange. From the user perspective, these classes
involve unsynchronized and synchronized communication.
PROFINET IO differentiates the following classes for RT
communication.
They differ not in terms of performance but in determinism.
11.2 Real-Time class 2 (RT2) – Not synchronized
In real-time class 2 frames are transmitted via unsynchronized
communication (anysochronous communication).
To activate the real-time class 2 both the IO controller and the IO
device must be set exactly the same as "Not synchronized". To do
this proceed as follows.
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