RTL8208B-LF/RTL8208BF-LF
Datasheet
7.10. Crossover Detection and Auto Correction
During the link setup phase, the RTL8208B(F)-LF checks whether it receives active signals on each port
in order to determine if a connection can be established. In cases where the RTL8208B(F)-LF receiver
data pin pair is connected to the receiver data pin pair of the peer device, or vice versa, the
RTL8208B(F)-LF will automatically change its configuration to swap receiver data pins with transmitter
data pins. If a port is connected to a PC or NIC with MDI-X interface with a crossover cable, the
RTL8208B(F)-LF will reconfigure the port to ensure proper connection. This effectively replaces the DIP
switch commonly used for reconfiguring a port on a hub or switch.
By pulling-up EN_AUTOXOVER, the RTL8208B(F)-LF identifies the type of connected cable and sets
the port to MDI or MDIX. When switching to MDI mode, the RTL8208B(F)-LF uses TXOP/N as
transmit pairs; when switching to MDIX mode, the RTL8208B(F)-LF uses RXIP/N as transmit pairs. The
same is true for the receive pairs. This function is port-based. Pulling-down EN_AUTOXOVER disables
this function and the RTL8208B(F)-LF operates in MDI mode, in which TXOP/N represents transmit
pairs, and RXIP/N represents receive pairs.
Note: IEEE 802.3 compliant forced mode 100M ports with Autoxover have link problems with NWAY
(Auto-Negotiation) ports. It is recommended to NOT use Autoxover for forced 100M.
7.11. Polarity Detection and Auto Correction
For better noise immunity and lower interference to ambient devices, the Ethernet electrical signal on a
twisted pair cable is transmitted in differential form. That is, the signal is transmitted on two wires in each
direction with inverse polarities (+/-). If wiring on the connector is faulty, or a faulty transformer is used,
the two inputs to a transceiver may carry signals with opposite but incorrect polarities. As a direct
consequence, the transceiver will not work properly.
When the RTL8208B(F)-LF operates in 10Base-T mode, it automatically reverses the polarity of its two
receiver input pins if it detects that the polarities of the incoming signals on the pins is incorrect. However,
this feature is unnecessary when the RTL8208B(F)-LF is operating in 100Base-TX mode.
Single-Chip Octal 10/100-TX/FX PHY Transceiver
46
Track ID: JATR-1076-21 Rev. 1.3
REALTEK [ Realtek Semiconductor Corp. ]
