BCM5722 Programmer’s Guide
10/15/07
Broadcom Corporation
Page 35 10BT/100BTx/1000BASE-T Transceiver Document 5722-PG101-R
10BT/100BTX/1000BASE-T TRANSCEIVER
Refer to the PHY transceiver data sheet for hardware architectural details of the triple-speed Ethernet PHY transceiver
integrated in BCM5722 Ethernet controllers.
AUTO-NEGOTIATION
The BCM5722 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 BCM5722 Ethernet controllers
automatically choose the mode of operation by advertising its abilities and comparing them with those received from its link
partner. The BCM5722 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 BCM5722 Ethernet controllers can perform an automatic MDI crossover when the
Disable Automatic MDI Crossover bit in the PHY Extended Control register (see “PHY Extended Control Register
(PHY_Addr = 0x1, Reg_Addr = 10h)” on page 428) is disabled, thus eliminating the need for crossover cables or cross-wired
(MDIX) ports. During auto-negotiation, the BCM5722 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 BCM5722 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 BCM5722 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.
WIRE SPEED
Wire speed is a mode which controls the auto-negotiation advertising. At startup, all the 100BASE-T (TX) and 1000BASE-T
(Gigabit) modes selected in MII registers 4 and 9 are advertised. If the same Highest Common Denominator (HCD) fails to
link five consecutive times, then the highest ability not already masked out is masked out. When both 100BTX and Gigabit
abilities are masked out and the same HCD fails five consecutive times, then all the advertised abilities in MII registers 4 and
9 are advertised. Whenever TX and Gigabit is masked out, then the wire speed downgrade is active, indicating that not all
the requested advertised abilities are actually advertised to the Link Partner.
Note: BCM5906 and BCM5906M are 10/100 devices only and use a 10/100-Mbps speed transceiver.
Note: The 10BASE-T ability is advertised as requested per MII register 4 at all times and is not affected by the
wire speed mode. Also, the wire speed mode never masks out Gigabit or 100BTX abilities unless there are other
abilities available to advertise.
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