Prioritized Startup - Siemens SIMATIC ET 200AL System Manual

Distributed i/o system

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5.12 Accelerating startup

● Configured RT class of the IO device

Startup time and RT class of the IO device

An IO device with IRT communication requires longer than an IO device with RT

communication for the accelerated startup.

The longer startup for IRT is due to the necessity of synchronizing the IO device before

the communication can be set up.

IWLAN and prioritized startup

PROFINET devices which are connected via access points to PROFINET IO do not

support the "Prioritized startup" PROFINET function.

Prioritized startup

Prioritized startup refers to the PROFINET function for accelerating the startup of IO devices

in a PROFINET IO system with RT communication. It shortens the time that the respective

configured IO devices require in order to reach the cyclic user data exchange in the following

● After the power supply has returned

● After a station has returned

● After activation of IO devices

Data exchange despite multiple use IP addresses/device names in PROFINET IO system

To achieve higher ramp-up times, the IO controller checks the uniqueness of device name

of IP address parallel to the device ramp-up. In the case of incorrect or double assignment

of device name or IP address, a short-time data exchange is possible until the IO controller

reacts to the error. In this time the IO controller can exchange IO data with the false device.

During commissioning, ensure that no IP addresses / device names are assigned multiple

times in the PROFINET IO system.

PROFINET with STEP 7 V15

Function Manual, 12/2017, A5E03444486-AH

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