Siemens SINAMICS DCM Operating Instructions Manual page 383

Update times and send cycles for RT classes
Definition of 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 time.
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
● Send cycles supported in the PROFINET devices assigned to a synchronization domain.
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- 11 Adjustable send cycles and update times
Send cycle
Range 250, 500,
"even" 1000 µs
1)
2000 µs
4000 µs
Range 375, 625, 750,
"uneven" 875, 1125,
3)
1250 to
3875 µs
(increment
125 µs)
Note
There is no intersection between the send cycles for the "even" and "uneven" ranges.
Explanations for the above table:
1) It is only possible to set send cycles from the "even" range when IO devices with RT class
"RT" are assigned to a synchronization domain. Likewise, only the reduction ratios from the
"even" range can be set for a send cycle setting from the "even" range.
SINAMICS DCM DC Converter
Operating Instructions, 1.2012, C98130-A7066-A1-05-7619
1 ms is an example of a typical send cycle.
Reduction ratios between update time and send cycle
RT
IRT "high flexibility"
1,2,4,8,16,32,64,128,256,512
1,2,4,8,16,32,64,128,256
1,2,4,8,16,32,64,128
Not supported 5)
IRT "high performance"
4)
1,2,4,8,16
1,2,4,8,16
1,2,4,8,16
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Descriptions of functions
10.3 PROFINET IO
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