MDI / MDI-X autocrossover function
The advantage of this 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.
Note
Formation of loops
Please note that the direct connection of two ports on the switch or accidental connection over
several switches causes an illegal loop. Such a loop can lead to network overload and network
failures.
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 a 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 a 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.
Auto polarity exchange
If the pair of receiving cables is incorrectly connected, in other words, RD+ and RD- are swapped
over, the polarity is reversed automatically.
Connecting up
5.6 Attachment to Industrial Ethernet
SCALANCE X-200
72
Operating Instructions, 11/2021, C79000-G8976-C284-15
