Real-Time (Rt) And Isochronous Real-Time (Irt) Communication - Siemens SINAMICS DCM Operating Instructions Manual

Descriptions of functions
10.3 PROFINET IO
10.3.2.2

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 these requirements are important. PROFINET meets these
requirements and is, therefore, implemented as a deterministic real-time network as follows:
● Transmission of time-critical data takes place at guaranteed time intervals. To achieve
● It is possible to predict the exact time at which data transmission will take place.
● Problem-free communication using other standard protocols is guaranteed within the
Definition: Isochronous real-time communication (IRT)
Isochronous real-time Ethernet: Real-time properties of PROFINET IO where IRT telegrams
are transmitted deterministically via scheduled communication paths in a defined sequence
to achieve the best possible synchronism and performance. This is also known as time-
scheduled communication and uses knowledge about the network structure. IRT requires
special network components that support scheduled data transmission.
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.
Figure 10-27 Bandwidth distribution/reservation, PROFINET IO IRT
Note
Currently, only communication via PROFINET IO with RT is possible when operating S7-300
stations with SINAMICS drives.
344
this, PROFINET provides an optimized communications channel for real-time
communication: Real time (RT).
same network.
SINAMICS DCM Control Module
Operating Instructions, 06.2010, C98130-A7067-A1-02-7619