PROFINET RT and IRT offer cycle times from 1 ms to 512 ms, but a wrong send clock setting or GSDML version mismatch causes cyclic data dropouts that look identical to cable faults. This article explains RT versus IRT differences, correct controller role assignment on Schneider Modicon M580 Unity Pro XL and ABB AC500 CM589-PNIO, and a six-step diagnostic workflow using Wireshark, the STEP 7 / Unity Pro diagnostic buffer, and a PROFINET tester.
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