3 rt classes, 1 rt classes for profinet io – Efficient Networks Siemens Sinamics S120 User Manual
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Communication PROFIBUS DP/PROFINET IO
10.3 Communications via PROFINET IO
Drive Functions
444
Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4
10.3.3
RT classes
10.3.3.1 RT classes for PROFINET IO
Description
PROFINET IO is a scalable realtime communications system based on Ethernet technology.
The scalable approach is expressed with three realtime classes.
RT
The RT communication is based on standard Ethernet. The data is transferred via prioritized
Ethernet message frames.
IRTflex
This realtime class is not supported in FW 2.5 SP1.
IRTtop
In addition to the bandwidth reservation, the message frame traffic can be further optimized
by configuring the topology. This enhances the performance during data exchange and the
deterministic behavior. The IRT time interval can thus be further optimized or minimized
compared with IRTflex.
In addition to the isochronous data transfer, with IRT even the application (position control
cycle, IPO cycle) can be synchronized in the devices. This is an essential requirement for
closed-loop axis control and synchronization via the bus.
Table 10-33 Comparison between RT and IRTtop
RT class
RT
IRTtop
Transfer mode
Switching based on the MAC address;
prioritization of the RT message frame
possible using Ethernet-Prio (VLAN
tag)
Path-based switching using a topology-
based planning; no transmission of
TCP/IP frames in the IRTtop interval.
MinDeviceInterval
Typically 2-8 msec
Fully deterministic, also for 250 µsec
Isochronous application
-
Yes
Start time of the isochronous
application
-
Times for receiving the data scheduled
exactly. A synchronous application can
be started directly afterwards (similar to
DP)
Determinism
Variance of the transmission duration
by started TCP/IP message frames
Exactly planned transfer; times for
transmission and receiving are
guaranteed for any topologies.
Reload the network configuration after
a change
-
Whenever the topology or the
communication relationships
change
Cross-traffic (controller-controller)
-
Yes