10BT/100BTx/1000BASE-T Transceiver
BCM5718 Programmer’s Guide
Broadcom
®
January 29, 2016 • 5718-PG108-R
Page 62
10BT/100BTx/1000BASE-T Transceiver
Auto-Negotiation
The Ethernet controller devices negotiate their mode of operation over the twisted-pair link using the auto-
negotiation mechanism defined in the IEEE 802.3u and IEEE 802.3ab specifications. Auto-negotiation can be
enabled or disabled by hardware or software control. When the auto-negotiation function is enabled, the
Ethernet controllers automatically choose the mode of operation by advertising its abilities and comparing them
with those received from its link partner. The Ethernet controllers can be configured to advertise 1000BASE-T
full-duplex and/or half-duplex, 100BASE-TX full-duplex and/or half-duplex, and 10BASE-T full-duplex and/or
half-duplex. The transceiver negotiates with its link partner and chooses the highest operating speed and duplex
that are common between them. Auto-negotiation can be disabled for testing or for forcing 100BASE-TX or
10BASE-T operation, but is always required for normal 1000BASE-T operation.
Automatic MDI Crossover
During auto-negotiation, one end of the link must perform an MDI crossover so that each transceiver’s
transmitter is connected to the other receiver. The Ethernet controllers can perform an automatic MDI crossover
when the Disable Automatic MDI Crossover bit in the PHY Extended Control register is disabled, thus
eliminating the need for crossover cables or cross-wired (MDIX) ports. During auto-negotiation, the Ethernet
controllers normally transmit on TRD
{0} and receive on TRD
{1}. When connected to another device that does
not perform the MDI crossover, the Ethernet controller automatically switches its transmitter to TRD
{1} and its
receiver to TRD
{0} to communicate with the remote device. If two devices that both have MDI crossover
capability are connected, an algorithm determines which end performs the crossover function. During
1000BASE-T operation, the Ethernet controllers swap the transmit symbols on pairs 0 and 1 and pairs 2 and 3
if auto-negotiation completes in the MDI crossover state. The 1000BASE-T receiver automatically detects pair
swaps on the receive inputs and aligns the symbols properly within the decoder.
PHY Control
The NetXtreme/NetLink Ethernet controller supports the following physical layer interfaces:
• The MII is used in conjunction with 10/100 Mbps copper Ethernet transceivers.
• GMII supports 1000 Mbps copper Ethernet transceivers.
MII Block
The MII interconnects the MAC and PHY sublayers (as shown in
).