PROFINET IO, real time or not ??

General, S7-1200, S7-300, S7-400, Simatic Step7 Add comments

Small article about one feature of profinet

Inspired by some discussion when I plan to apply profinet IO, one of constrain to apply profinet is cause of profinet based on ethernet, it is feared that communication data is not real time. As we know in process automation requires punctual and deterministic data transmission.

To solve this constrain, for cyclic exchange or critical I/O, Profinet IO doesn’t use TCP/IP, it uses Real-Time communication (RT) or Isochronous Real-Time communication (IRT) for synchronized data transmission.

REAL-TIME communication (RT)

Profinet IO with real-time communication (RT) is optimum solution for integrating IO system. This system use standard ethernet in the devices and available for industrial switch and special hardware is not required. Profinet IO message frames have priority over standard message frames. The data is transferred via prioritized ethernet message frames. We can realize update times from 250 us with RT communication.

ISOCHRONOUS REAL-TIME communication (IRT)

Transmission procedure cyclic exchange between Profinet devices needs synchronized procedure transmission which can be set at HWConfig at Simatic Manager. Next time, I will expain about how to configure IRT and synchronize master slave at hardware config Simatic Manager 🙂

IRT has two option configuration, consist of IRT with high flexibility and IRT with high performance.

The figure above is explained about data frames and time interval within a send clock cycle 1000 us (1 ms). Let’s see the orange and white area, reserved transmission bandwith for IRT is as a proportion of the max, possible transmission of cyclic user data 30 % of 500 us (150 us). Green area (RT data) is cyclic RT frames prioritized according to urgency in level 6/high (Profinet IO). Priority level of RT data based on IEEE 802.1Q

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