Fragmentation - Siemens SIMATIC ET 200AL System Manual

STEP 7 shows the DFP groups in "Domain management" > "Sync domains" > "Name of the
sync domain" > "Device" in the "IO devices" box.
Figure 5-56
Note
Dynamic frame packing with high watchdog times
If you set the parameter "Accepted update cycles without IO data" higher than 31, Dynamic
Frame Packing does not place this IO device in a DFP group.
5.6.2

Fragmentation

The transfer of a complete standard Ethernet frame with TCP/IP data takes up to 125 µs.
This means that the cycle time for PROFINET IO data cannot be reduced by any desired
amount.
The performance upgrade uses the fragmentation procedure, which breaks down TCP/IP
frames into sub-frames. These frame segments are transferred to the target device over
multiple send clocks; there they are reassembled to the original TCP/IP frame.
Fragmentation is a requirement for cycle times lower than 250 µs. In these short send
clocks, you can use more bandwidth for cyclic IO data, since the fragments of the standard
Ethernet frames use significantly less bandwidth than a complete standard Ethernet frame.
PROFINET with STEP 7 V15
Function Manual, 12/2017, A5E03444486-AH
Display of the DFP groups in STEP 7
5.6 PROFINET with performance upgrade
Functions
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