Siemens SIMATIC NET SCALANCE XC-300 Operating Instructions Manual page 63

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 at 100 Mbps
or 10 Mbps half duplex mode.
• If you disable the "Auto negotiation" function, the "MDI/MDI-X autocrossover" function is also
turned off. Then use a crossover cable.
Fast Retrain
The devices support the Fast Retrain function in accordance with standard IEEE 802.3. The Fast
Retrain function ensures that no link interruptions occur in the case of electromagnetic
interferences (EMI) on the connection cable to the partner.
If a Fast Retrain event occurs, the device tries to reestablish the communication to the partner
device for a duration of up to 30 ms. Only if this is unsuccessful, is the link disconnected.
During the Fast Retrain procedure no telegrams are transferred via the affected connection.
Note
The function is always enabled and cannot be deactivated.
The function is relevant only for 10 Gbps ports.
There are no Fast Retrain events for port speeds ≤ 1 Gbps.
SCALANCE XC-300
Operating Instructions, 10/2022, C79000-G8976-C584-01
Connecting up
6.5 Industrial Ethernet
63