Siemens SCALANCE X-200 Operating Instructions Manual page 56

Product properties
3.10 SCALANCE XF204-2
Autonegotiation
Autonegotiation means the automatic detection of the functionality of the port at the opposite
end. Using autonegotiation, repeaters or end devices can detect the functionality available at
the port of a partner device allowing automatic configuration of different types of device. With
autonegotiation, two components connected to a link segment can exchange parameters
and set themselves to match the supported communication functionality.
Note
If an IE switch port operating in autonegotiation mode is connected to a partner device that is
not operating in autonegotiation mode, the partner device must be set permanently to half
duplex mode.
If an IE switch port is set permanently to full duplex, the connected partner device must also
be set to full duplex.
If the autonegotiation function is disabled, the MDI/MDI-X autocrossover function is also
inactive. This means it may be necessary to use a crossover cable.
Note
The SCALANCE XF204-2 is a plug-and-play device that does not require settings to be
made for commissioning.
MDI / MDIX autocrossover function
The advantage of the MDI / MDIX autocrossover function is that straight-through cables can
be used throughout and external Ethernet crossover cables are unnecessary. This prevents
malfunctions resulting from mismatching send and receive wires. This makes installation
much easier for the user.
IE Switches X-200 support the MDI / MDIX autocrossover function.
NOTICE
Please note that a direct connection of two ports on the switch or an accidental connection
across several switches causes a forbidden loop. Such a loop can lead to network overload
and network failures.
Auto polarity exchange
If the pair of receiving cables are incorrectly connected (RD+ and RD- swapped over), the
polarity is reversed automatically.
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Operating Instructions, 12/2011, A5E00349864-19
SCALANCE X-200