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194 Software Developer’s Manual
PHY Functionality and Features
11.6 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 11-2 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 11-2. Overview of Link Establishment
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