Functions
5.5 Real-time communication
PROFINET with STEP 7 V15
178 Function Manual, 12/2017, A5E03444486-AH
Comparison of RT and IRT
The most important differences between RT and IRT
Table 5- 2 Comparison between RT and IRT
Transmission method Prioritizing the RT frames through
Ethernet priority (VLAN tag)
Path-based switching on the basis of a communi-
cation path plan; no transmission of TCP/IP fra-
mes in the time range with IRT communication.
Determinism Variance of the duration of trans-
mission by the shared use of the
transmission bandwidth with other
Exact, planned transmission, transmission and
reception times are guaranteed for all topologies.
Hardware support through special
Ethernet controllers is required
Not required Required
Starting time of the isochronous
application
- The point in time for the reception of the data is
planned exactly. Application can be started syn-
Configuring PROFINET IO with IRT
Introduction
If you want to configure a PROFINET IO system with IRT, you have to configure the
PROFINET IO devices. These PROFINET devices must support IRT. Set which device acts
as the sync master and synchronizes the other devices. This is done by configuring a sync
domain with a sync master and at least one sync slave.
● There is an IO system with an IO controller and at least one IO device.
● You have configured the topology for the IO system.
● The devices support IRT.
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