Siemens SIMATIC S7-400H System Manual page 73

Note
Networking PROFINET components
The PROFINET interfaces of our devices are set to "automatic setting" (autonegotiation) by
default. Verify that all devices connected to the PROFINET interface of the CPU are also set
to the "Autonegotiation" mode. This is the default setting of standard PROFINET / Ethernet
components.
If connecting a device to the on-board PROFINET interface of the CPU that does not support
the "automatic setting" (Autonegotiation) operating mode, or selecting a setting other than
the "automatic setting" (Autonegotiation), note the following:
 PROFINET IO needs to be operated at 100 Mbps in full-duplex mode, which means if the
 Operation at 100 Mbps full-duplex is possible if the on-board PROFINET interface(s) of
Background: If a switch that is permanently set to 10 Mbps half-duplex is connected to the
interface of the CPU, the "Autonegotiation" setting forces the CPU to adapt itself to the
settings of the partner device, i.e. the communication operates de facto at "10 Mbps half-
duplex". However, this would not be a valid operating mode because PROFINET IO
demands operation at 100 Mbps full-duplex.
Reference
● For additional information on PROFINET, refer to PROFINET System Description
● For detailed information about Ethernet networks, network configuration and network
● For additional information about PROFINET, refer to: PROFINET
S7-400H
System Manual, 03/2012, A5E00267695-11
on-board PROFINET interface of the CPU for PROFINET IO communication and
Ethernet communication is used at the same time, the PROFINET interface may only be
operated at 100 Mbps in full-duplex mode.
the CPU is(are) used for Ethernet communication only. Half-duplex mode is not allowed
in any situation.
(http://support.automation.siemens.com/WW/view/en/19292127)
components refer to the SIMATIC NET manual: Twisted-pair and fiber-optic networks
(http://support.automation.siemens.com/WW/view/en/8763736) manual.
(http://www.profibus.com/)
Assembly of a CPU 41x–H
5.9 PROFINET interface (X5)
73