Siemens SCALANCE XR-300WG Series Operating Instructions Manual page 38

Connecting up
5.2 Industrial Ethernet
MDI / MDI-X autocrossover
With the MPI/MDI-X autocrossover function, the send and receive contacts of an Ethernet
port are assigned automatically. The assignment depends on the cable with which the
communications partner is connected. This means that it does not matter whether the port is
connected using a patch cable or crossover cable. 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 IE switch or accidental connection
over several IE switches causes an illegal loop. Such a loop can lead to network overload
and network failures.
Autonegotiation
Autonegotiation means the automatic detection/negotiation of the transmission rate and the
operating mode of ports at the opposite end. This makes it possible to configure different
devices automatically.
Two components connected to a link segment can exchange information about the transfer
and can adapt their settings to each other. The mode with the highest possible speed is set.
Note
• If a port is set permanently to full duplex, the connected partner port must also be set to
full duplex.
• If a port operating in the "Auto negotiation" mode is connected to a partner port that is not
operating in the"Auto negotiation" mode, the partner port setting must be fixed.
• Devices not supporting "Auto negotiation" must be set permanently to 100 Mbps or
10 Mbps half duplex.
• If you disable the "Auto negotiation" function, the "MDI/MDI-X autocrossover" function is
also turned off. Then use a crossover cable.
38
Operating Instructions, 05/2017, C79000-G8976-C454-01
SCALANCE XR-300WG