PROFINET and Isochronous Communication
The isochronous data exchange with PROFINET is defined in the isochronous real-time (IRT) concept. PROFINET IO field devices with IRT functionality have switch ports integrated in the field device. They can be based e.g. on the Ethernet controllers ERTEC 400/200. The data exchange cycles are usually in the range of a few hundred microseconds up to a few milliseconds. The difference to real-time communication is essentially the high degree of determinism, so that the start of a bus cycle is maintained with high precision. The start of a bus cycle can deviate up to 1 µs (jitter). IRT is required, for example, for motion control applications (positioning control processes).
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