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Intel
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82575EB Gigabit Ethernet Controller — Determining Link State
Intel
®
82575EB Gigabit Ethernet Controller 324632-003
Software Developer’s Manual and EEPROM Guide Revision: 2.1
264 January 2011
11.2 Determining Link State
The PHY and its link partner determine the type of link established through one of three methods:
• Auto-Negotiation
• Parallel Detection
• Forced Operation
Auto-Negotiation is the only method allowed by the 802.3ab standard for establishing a 1000BASE-T
link, although forced operation could be used for test purposes. For 10/100 links, any of the three
methods can be used. The sections that follow discuss each in greater detail.
Figure 29 provides an overview of link establishment. First the PHY checks if Auto-Negotiation is
enabled. By default, the PHY supports Auto-Negotiation (PHY register 0, bit 12). If not, the PHY forces
operation as directed. If Auto-Negotiation is enabled, the PHY begins transmitting Fast Link Pulses
(FLPs) and receiving FLPs from its link partner. If FLPs are received by the PHY, Auto-Negotiation
proceeds. It also can receive 100BASE-TX MLT3 and 10BASE-T Normal Link Pulses (NLPs). If either
MLT3 or NLPs are received, it aborts FLP transmission and immediately brings up the corresponding
half-duplex link.
Figure 29. Overview of Link Establishment
11.2.1 False Link
The PHY does not falsely establish link with a partner operating at a different speed. For example, the
PHY does not establish a 1000 Mb/s or 10 Mb/s link with a 100 Mb/s link partner.
Power-Up, Reset,
Link Failure
Start
A/N
Enabled
?
Speed
0.13
?
No
Send FLP
Send NLP
0 = 10M
Send IDLES
1 = 100M
Detect
10Mbps
?
Link
Down
No
Link
Up
Yes
Detect
10Mbps
?
Take
Link
Down
No
Take
Link
Up
Yes
Detect
FLP
Auto
Negotiate
Detect
IDLES
Detect
NLP
10M
Half-Duplex
Link
Yes
No
Parallel
Detect
100M
Half-Duplex
Link
Yes
No
Yes
Yes