Siemens SIMATIC ET 200AL, System Manual

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Functions
5.5 Real-time communication
PROFINET with STEP 7
Function Manual, 05/2021, A5E03444486-AL
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5.5.4 Comparison of RT and IRT
The most important differences between RT and IRT
Table 5- 2 Comparison between RT and IRT
Property RT IRT
Transmission method Prioritizing the RT frames through Ethernet
priority (VLAN tag)
Path-based switching on the basis of a
communication path plan; no transmis-
sion of TCP/IP frames in the time range
with IRT communication.
Determinism Variance of the duration of transmission by
the shared use of the transmission band-
width with other protocols (e.g., TCP/IP)
Exact, planned transmission, transmis-
sion and reception times are guaranteed
for all topologies.
Hardware support through special
Ethernet controllers is required
Not required Required
Isochronous application - Yes
Starting time of the isochronous
application
- The point in time for the reception of the
data is planned exactly. Application can
be started synchronized to the cycle.
5.5.5 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.
Requirement
• 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.