Siemens SIMATIC ET 200SP Manual page 17

Isochronous real-time communication
Synchronized transmission method for cyclic exchange of IRT data between PROFINET
devices. A reserved bandwidth within the send clock is available for IRT data. The reserved
bandwidth ensures that the IRT data can also be transferred without being affected by
another high network load (e.g. TCP/IP communication or additional real time
communication) at reserved, chronologically synchronized intervals.
A topological configuration is required for IRT.
Note
IO controller as sync master with IRT communication
We recommend also operating the IO controller as a sync master when configuring the IRT
communication.
Otherwise, IO devices with IRT and RT configuration could fail as a result of sync master
failure.
You can find more information on the configuration of synchronized PROFINET devices in
sync domains in the STEP 7 online help and
● As of STEP 7 V12, in the PROFINET with STEP 7 V13
(http://support.automation.siemens.com/WW/view/en/49948856) function manual.
● As of STEP 7 V5.5, in the system manual PROFINET System Description
(http://support.automation.siemens.com/WW/view/en/19292127).
IM 155-6 PN HF interface module (6ES7155-6AU00-0CN0)
Manual, 03/2015, A5E03915895-AF
Product overview
2.2 Functions
17