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Forced Operation — Intel
®
82575EB Gigabit Ethernet Controller
324632-003 Intel
®
82575EB Gigabit Ethernet Controller
Revision: 2.1 Software Developer’s Manual and EEPROM Guide
January 2011 265
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, programmers can command the PHY to
do one of the following:
• Force twisted-pair link operation to:
— 1000-T Full Duplex
— 1000-T Half Duplex
— 100-TX, Full Duplex
— 100-TX, 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.
11.2.2 Forced Operation
Forced operation can be used to establish 10 and 100 links, and 1000 links for test purposes. In this
method, Auto-Negotiation is disabled completely and the link state of the PHY is determined by PHY
register 0d.
Note: When speed is forced, the MDI/MDI-X crossover feature is not functional.
In forced operation, the programmer sets the link speed (10, 100, or 1000) and duplex state (full or
half). For Gigabit (1000) links, the programmer must explicitly designate one side as the Master and
the other as the Slave. Table 85 summarizes link establishment procedures.
11.2.3 Auto Negotiation
The PHY supports the IEEE 802.3u Auto-Negotiation scheme with next page capability. Next Page
exchange uses PHY register 7d to send information and PHY register 8d to receive them. Next Page
exchange can only occur if both ends of the link advertise their ability to exchange Next Pages.
Table 85. 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.