Data Sheet

Interconnects—Ethernet Controller I210
115
The PHY does not falsely establish link with a partner operating at a different speed. For example, the
PHY does not establish a 1 Gb/s or 10 Mb/s link with a 100 Mb/s link partner.
When the PHY is first powered on, reset, or encounters a link down state; it must determine the line
speed and operating conditions to use for the network link.
The PHY first checks the MDIO registers (initialized via the hardware control interface or written by
software) for operating instructions. Using these mechanisms, designers can command the PHY to do
one of the following:
• Force twisted-pair link operation to:
— 1000T, full duplex
— 1000T, half duplex
— 100TX, full duplex
— 100TX, half duplex
— 10BASE-T, full duplex
— 10BASE-T, half duplex
• Allow auto-negotiation/parallel-detection.
In the first six cases (forced operation), the PHY immediately begins operating the network interface as
commanded. In the last case, the PHY begins the auto-negotiation/parallel-detection process.
3.7.8.1.2 Forced Operation
Forced operation can be used to establish 10 Mb/s and 100 Mb/s links, and 1000 Mb/s links for test
purposes. In this method, auto-negotiation is disabled completely and the link state of the PHY is
determined by MII Register 0.
In forced operation, the designer sets the link speed (10, 100, or 1000 MB/s) and duplex state (full or
half). For GbE (1000 MB/s) links, designers must explicitly designate one side as the master and the
other as the slave.
Note: The paradox (per the standard): If one side of the link is forced to full-duplex operation and
the other side has auto-negotiation enabled, the auto-negotiating partner parallel-detects to
a half-duplex link while the forced side operates as directed in full-duplex mode. The result is
spurious, unexpected collisions on the side configured to auto-negotiate.
Table 3-30 lists link establishment procedures.
Table 3-30. Determining Duplex State Via Parallel Detection
Configuration Result
Both sides set for auto-negotiate Link is established via auto-negotiation.
Both sides set for forced operation No problem as long as duplex settings match.
One side set for auto-negotiation and the other for forced, half-
duplex
Link is established via parallel detect.
One side set for auto-negotiation and the other for forced full-
duplex
Link is established; however, sides disagree, resulting in
transmission problems (Forced side is full-duplex, auto-
negotiation side is half-duplex.).