Efficient Networks S120 manual RT classes for Profinet IO Description, IRTflex, IRTtop

Communication PROFIBUS DP/PROFINET IO 10.3 Communications via PROFINET IO

10.3.3RT classes

10.3.3.1RT 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;	Path-based switching using a topology-
	prioritization of the RT message frame	based planning; no transmission of
	possible using Ethernet-Prio (VLAN	TCP/IP frames in the IRTtop interval.
	tag)
MinDeviceInterval	Typically 2-8 msec	Fully deterministic, also for 250 µsec
Isochronous application	-	Yes
Start time of the isochronous	-	Times for receiving the data scheduled
application		exactly. A synchronous application can
		be started directly afterwards (similar to
		DP)
Determinism	Variance of the transmission duration	Exactly planned transfer; times for
	by started TCP/IP message frames	transmission and receiving are
		guaranteed for any topologies.
Reload the network configuration after	-	Whenever the topology or the
a change		communication relationships
		change
Cross-traffic (controller-controller)	-	Yes

444	Drive Functions
	Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4