Siemens SINAMICS DCM Operating Instructions Manual page 381

In addition to the isochronous data transmission function provided by IRT, even the
application itself (position control cycle, IPO cycle) can be isochronous in the devices. This is
an essential requirement for closed-loop axis control and synchronization via the bus.
Isochronous data transmission with cycle times well below one millisecond and with a
deviation in the cycle start (jitter) of less than a microsecond provide sufficient performance
reserves for demanding motion control applications.
The RT classes IRT "high flexibility" and IRT "high performance" can be selected as options
in the synchronization settings configuration area of HW Config. In the description below,
both these classes are simply referred to as "IRT".
In contrast to standard Ethernet and PROFINET IO with RT, the telegrams for PROFINET IO
with IRT are transmitted according to a schedule.
Comparison between RT and IRT
Table 10- 10 Comparison between RT and IRT
RT class
Transmission mode
Isochronous application
in the IO controller
Determinism
Reload the network
configuration after a change
Maximum switching depth
(number of switches in one
line)
For possible send cycles, see subitem "Send cycles and update times for RT classes" in table "Adjustable send cycles and
update times"
Note
SINAMICS DCM does not support isochronous communication.
SINAMICS DCM DC Converter
Operating Instructions, 1.2012, C98130-A7066-A1-05-7619
RT
Switching based on the MAC
address; prioritization of the
RT telegrams possible using
Ethernet-Prio (VLAN tag)
No
Variance of the transmission
duration by started TCP/IP
telegrams
Not relevant
10 at 1 ms
IRT "high flexibility"
Switching using the MAC
address;
bandwidth reservation by
reserving an IRT "high
flexibility" interval in which
only IRT "high flexibility"
frames are transferred but,
for example, no TCP/IP
frames
No
Guaranteed transmission of
the IRT "high flexibility"
telegrams in the current
cycle thanks to reserved
bandwidth
Only when the size of the
IRT "high flexibility" interval
needs to be modified
(position reservation is
possible)
61
Descriptions of functions
10.3 PROFINET IO
IRT "high performance"
Path-based switching
according to a topology-
based schedule; no
transmission of TCP/IP
frames and IRT "high
flexibility" frames in the IRT
"high performance" interval
Yes
Precisely scheduled
transmission; times for
transmitting and receiving
are guaranteed for any
topologies.
Whenever the topology or
the communication
relationships
change
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