Chapter 10. Real-Time Class Communication; Real-Time Classes In Profinet Io; Real-Time Class 2 (Rt2) - Not Synchronized; Real-Time Class 3 (Irt_Top) (Rt3) - Datalogic AMT58 Series Manual

CHAPTER 10
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 millisec-
onds 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 real-time communication differs from real-time communica-
tion mainly in its isochronous behavior: the start of a bus cycle can deviate by a maxi-
mum of 1 µs (jitter is less than 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.

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 per-
spective, 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.

REAL-TIME CLASS 2 (RT2) - NOT SYNCHRONIZED

In real-time class 2, frames are transmitted via unsynchronized communication (asyn-
chronous communication).
To activate the real-time class 2 both the IO controller and the IO device must be set the
same as "Not synchronized".

REAL-TIME CLASS 3 (IRT_TOP) (RT3)

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 real-time communication differs from real-time communica-
tion mainly in its isochronous behavior: the start of a bus cycle can deviate by a maxi-
mum of 1 µs (jitter is less then 1 µs).
This communication is required, for example, for high-accuracy closed-loop control
tasks.
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