RTL8211C & RTL8211CL
Datasheet
6.7. Crossover Detection and Auto-Correction
Ethernet needs a crossover mechanism between both link partners to cross the transmit signal to the
receiver when the medium is twisted-pair cable (e.g., CAT.3 or CAT.5 UTP). Crossover Detection &
Auto-Correction Configuration eliminates the need for crossover cables between devices, such as two PC’s
connected to each other with a CAT.3 or CAT.5 Ethernet cable. The basic concept is to assume the initial
default setting is MDI mode, and then check the link status. If no link is established after a certain time,
change to MDI Crossover mode and repeat the process until a link is established. An 11-bit pseudo-random
timer is applied to decide the mode change time interval.
Crossover Detection & Auto-Correction is not a part of the Auto-Negotiation process, but it utilizes the
process to exchange the MDI/MDI Crossover configuration. If the RTL8211C(L) is configured to only
operate in 100Base-TX or only in 10Base-T mode, then Auto-Negotiation is disabled only if the Crossover
Detection & Auto-Correction function is also disabled. If Crossover Detection & Auto-Correction are
enabled, then Auto-Negotiation is enabled and the RTL8211C(L) advertises only 100Base-TX mode or
10Base-T mode. If the speed of operation is configured manually and Auto-Negotiation is still enabled
because the Crossover Detection & Auto-Correction function is enabled, then the duplex advertised is as
follows:
1. If CONFIG is set to half duplex, then only half duplex is advertised.
2. If CONFIG is set to full duplex, then both full and half duplex are advertised.
If the user wishes to advertise only full duplex at a particular speed with the Crossover Detection &
Auto-Correction function enabled, then Auto-Negotiation should be enabled (register 0.12) with the
appropriate advertising capabilities set in registers 4 or 9. The Crossover Detection & Auto-Correction
function may be enabled/disabled by setting (register 16.6) manually.
After initial configuration following a hardware reset, Auto-Negotiation can be enabled and disabled via
register 0.12, speed via registers 0.13, 0.6, and duplex via register 0.8. The abilities that are advertised can
be changed via registers 4 and 9. Changes to registers 0.12, 0.13, 0.6, and 0.8 do not take effect unless at
least one of the following events occurs:
• Software reset (register 0.15)
• Restart of Auto-Negotiation (register 0.9)
• Transition from power-down to power-up (register 0.11)
Registers 4 and 9 are internally latched once each time Auto-Negotiation enters the ABILITY DETECT
state in the arbitration state machine (IEEE 802.3). Hence a write into register 4 or 9 has no effect once the
RTL8211C(L) begins to transmit Fast Link Pulses.
Integrated 10/100/1000 Gigabit Ethernet Transceiver
18
Track ID: JATR-1076-21 Rev. 1.3
ETC [ ETC ]
