Efficient Networks S120 manual Definition Real Time RT and determinism

Communication PROFIBUS DP/PROFINET IO 10.3 Communications via PROFINET IO

10.3.1.2Real-time (RT) and isochronous real-time (IRT) communication

Real-time communication

If supervisors are involved in communication, this can result in excessively long runtimes for the production automation system. When communicating time-critical IO user data, PROFINET therefore uses its own real time channel, rather than TCP/IP.

Definition: Real Time (RT) and determinism

Real time means that a system processes external events over a defined period. Determinism means that a system responds in a predictable manner (deterministically).

In industrial networks, both of these requirements are important. PROFINET meets these requirements. PROFINET is implemented as a deterministic real time network as follows:

●Transmission of time-critical data takes place at guaranteed time intervals. To achieve this, PROFINET provides an optimized communication channel for real time communication: Real Time (RT).

●An exact prediction of the time at which the data transfer takes place is possible.

●Problem-free communication using other standard protocols is guaranteed within the same network.

Definition: Isochronous real time communication (IRT)

Isochronous Real Time Ethernet: Real time properties of PROFINET IO where IRT telegrams are transmitted deterministically via planned communication paths in a defined sequence to achieve the best possible synchronism and performance. This is also known as time-scheduled communications whereby knowledge about the network structure is utilized. IRT requires special network components that support planned data transfer.

When the transfer procedure is implemented in the ERTEC ASICs (Enhanced Real-Time Ethernet Controller), this results in cycle times of at least. 500 μs and a jitter accuracy of less than 1 μs.

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Figure 10-45 Broadband distribution/reservation, PROFINET IO IRT

Note

When operating S7-300 stations with SINAMICS drives, presently only communications via PROFINET IO with RT are possible. For SIMOTION with SINAMICS drives, communications via PROFINET IO with IRT are possible.

438	Drive Functions
	Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4