Siemens SIMATIC PROFINET Function Manual page 179

Requirements for the fragmentation process (CPU 1518-4 PN/DP)
If you use the following combinations for send clock and bandwidth settings, the devices in
the IO system use the fragmentation process.
● Send clock cycle 125 µs: Always fragmentation irrespective of the bandwidth setting.
● Send clock cycle 187.5 µs: Fragmentation with the bandwidth settings "Maximum 50%
cyclic IO data. Balanced proportion." and "Maximum 90% cyclic IO data. Focus on cyclic
IO data."
The PROFINET IO interface of the controller supports fragmentation if all the ports except
one are deactivated.
Optimizing port settings for low send clocks
You can further optimize the bandwidth use in your PROFINET IO system by using cables
with a short cable length (< 20 m) or a short signal delay (max. 0.12 µs) between the
devices.
To configure cables with a shorter length or signal delay in STEP 7, follow these steps:
1. Select the port in the topology view of STEP 7.
2. Navigate in the Inspector window to "Port interconnection" in the "Partner port" box.
3. Select the option "Cable length" or "Signal delay:".
4. Select the cable length or enter the signal delay.
Figure 5-62
PROFINET with STEP 7 V14
Function Manual, 09/2016, A5E03444486-AG
Optimizing port settings for low send clocks
5.6 PROFINET with performance upgrade
Functions
179