Efficient Networks Siemens Sinamics S120 - Manual (Page 438)

Communication PROFIBUS DP/PROFINET IO
10.3 Communications via PROFINET IO
Drive Functions
438
Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4
10.3.1.2 Real-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.