Operation
7.6 Communication via PROFINET IO
SINAMICS DCP
248 Operating Instructions, 09/2019, A5E34382853K
7.6.1.1 Real-time (RT) and isochronous real-time (IRT) communication
Real-time communication
When communication takes place via TCP/IP, the resultant transmission times may be too
long and not defined to meet the production automation requirements. When communicating
time-critical IO user data, PROFINET IO therefore uses its own real-time channel, rather
than TCP/IP.
Real time means that a system processes external events over a defined period.
Determinism
Determinism means that a system will react in a predictable (deterministic) manner.
With PROFINET IO with IRT, it is possible to precisely determine (predict) transmission
times.
PROFINET IO with RT (Real Time)
Real-time data is treated with a higher priority than TCP(UDP)/IP data. Transmission of time-
critical data takes place at guaranteed time intervals. RT communication is the basis for data
exchange with PROFINET IO.
PROFINET IO with IRT (Isochronous Real Time)
Isochronous real time: Real-time property of PROFINET IO where IRT telegrams are
transferred deterministically via planned communication paths in a defined sequence to
achieve the best possible synchronism and performance between the IO controller and IO
device (drive unit). IRT is also known as time-scheduled communication whereby knowledge
about the network structure (topology) is utilized. IRT requires special network components
that support scheduled data transmission.
Minimum cycle times of 500 μs and a jitter accuracy of less than 1 μs can be achieved with
this transmission method.
Figure 7-38 Bandwidth distribution/reservation, PROFINET IO
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