Siemens SINAMICS Series Operating Instructions Manual page 505

Update cycles and send cycles for RT classes
Definition of the update time / send cycle
If we take a single IO device in the PROFINET IO system as an example, this device has
been supplied with new data (outputs) by the IO controller and has transferred new data
(inputs) to the IO controller within the update time. The send cycle is the shortest possible
update cycle.
All cyclic data is transferred within the send cycle. The actual send cycle that can be set
depends on various factors:
● Bus load
● Type of devices used
● Computing capacity available in the IO controller
● Supported send clocks in the participating PROFINET devices of a synchronization
domain. A typical send cycle is, e.g. 1 ms.
The table below specifies the reduction ratios which can be set between the send cycle and
the update times for IRT "high performance", IRT "high flexibility", and RT.
Table 10- 37 Settable send cycles and update cycles
Send cycle
Range 250, 500, 1000 µs
"even"
1)
2000 µs
4000 µs
Range 375, 625, 750, 875, 1125,
"odd" 1250 µs ... 3875 µs
3)
(increment 125 µs)
Explanations for the previous table:
It is only possible to set send cycles from the "even" range when IO devices with RT class "RT" are assigned to a
1)
synchronization domain. Likewise, only the reduction ratios from the "even" range can be set for a send cycle setting
from the "even" range.
It is generally only possible to set a reduction ratio of 1:1 between the update time and send cycle for IO devices
2)
(ET200S IM151-3 PN HS, SINAMICS S) which are operated in isochronous mode. In this case, the update time mode
must always be set to "fixed factor" (under "I/O device" properties, "IO cycle" tab, "Mode" drop-down menu). This means
that STEP 7 will not automatically adjust the update cycle and thus the update cycle will always correspond to the send
cycle.
The send cycles from the "uneven" range can be set only if a synchronization domain does not include any IO devices
3)
with RT class "RT". Likewise, only the reduction ratios from the "uneven" range can be set for a send cycle setting from
the "uneven" range.
Isochronous operation is not compatible with IRT "high flexibility".
4)
Uneven send cycles can be used only if the IO systems assigned to the synchronization domain do not include any RT
5)
or IRT "high flexibility" devices.
Furthermore, the send cycles which can actually be set are determined by the intersection of
the send cycles supported by all the devices in the synchronization domain.
SINAMICS DCM DC Converter
Operating Instructions, 12/2018, A5E34763375A
Reduction ratio between update and send cycles
RT
IRT "high flexibility"
4)
1, 2, 4, 8, 16, 32, 64, 128, 256, 512 1, 2, 4, 8, 16
1, 2, 4, 8, 16, 32, 64, 128, 256
1, 2, 4, 8, 16, 32, 64, 128
Not supported
5)
Descriptions of functions
10.5 Communication via PROFINET IO
IRT "high performance"
2)
1, 2, 4, 8, 16
2)
1, 2, 4, 8, 16
2)
1
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