Siemens SIMATIC ET 200MP Manual page 15

Isochronous real-time communication
Synchronized communication protocol for cyclic exchange of IRT data between PROFINET
devices. A reserved bandwidth is available in the send cycle for IRT data. The reserved
bandwidth ensures that IRT data can be transferred at reserved synchronized intervals,
without being influenced by other network loads (e.g., TCP/IP communication, or additional
real-time communication).
A topological configuration is required for IRT.
Note
IO controller as sync master with IRT communication
We recommend operating the IO controller as sync master when configuring IRT
communication.
Otherwise, IO devices with IRT and RT configuration could fail as a result of sync master
failure.
You can find additional information on 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 V14
(https://support.industry.siemens.com/cs/ww/en/view/49948856) function manual.
● as of STEP 7 V5.5 in the PROFINET System Description
(http://support.automation.siemens.com/WW/view/en/19292127) manual.
Interface module IM 155-5 PN ST (6ES7155-5AA01-0AB0)
Manual, 11/2017, A5E03612323-AC
Product overview
2.2 Functions
15