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3.0 Configuration (Continued)

The Auto-Negotiation priority resolution are as follows:

1. 1000BASE-T Full Duplex (Highest Priority)

2. 1000BASE-T Half Duplex

3. 100BASE-TX Full Duplex

4. 100BASE-TX Half Duplex

5. 10BASE-T Full Duplex

6. 10BASE-T Half Duplex (Lowest Priority)

3.3.2 Gigabit Speed Fallback

When gigabit mode is advertised, the default auto-negotia-

tion mode attempts to establish link at the highest common

denominator advertised. However, there are situations that

the cable media may not be appropriate for the gigabit

speed communication. If achieving a quality link is the

highest priority, the Speed Fallback Mode can be enabled.

The Speed Fallback Mode allows auto-negotiation to link at

the next lower speed advertised (100Mbps or 10Mbps) if

the gigabit mode fails.

There are three criteria established to initiate the gigabit

Speed Fallback.

1. Auto-negotiation failing to achieve a stable gigabit link

2. CRC error rate

3. Idle error rate

There are four basic control register bits used to configure

the Speed Fallback. Expanded register 0x1C0.3 = 1

enables the Speed Fallback mode. LED Control Register

0x13.2:0 selects the criteria for the Speed Fallback.

The default for AN Speed Fallback is that after five tries to

achieve a stable link, the link speed will drop down to the

next lower advertised speed. The default CRC and IE

Speed Fallback is that after five link drops due to increase

error rate, the link speed drops down to the next lower

advertised speed. If during the link retry stage that the link

partner drops the link or the CAT5 cable is unplugged, the

retry counter will reload the retry count with the default

value of five.

Note that the Speed Fallback works only from gigabit mode

to 100 Mbps or 10 Mbps.

3.3.3 Gigabit Retry Forced Link

Under the situations that the cable media may not be

appropriate for the gigabit transmission, it may take exces-

sive number of retries to achieve a stable link. If achieving

a stable link is the highest priority, the Retry Forced Link

Mode can be enabled. Retry Forced Link Mode allows

auto-negotiation to force link at the highest common link

speed after five retries.

There are two criteria established to initiate the gigabit

Retry Forced Link.

1. CRC error rate

2. Idle error rate

There are three basic control register bits used to configure

the Speed Fallback and Retry Forced Link. Expanded reg-

ister 0x1C0.3 = 0 enables the Retry Forced Link mode (i.e.,

teh default mode upon power up). LED Control Register

0x13.1:0 selects the criteria for the Speed Fallback. Since

Retry Forced Link does not work when AN fails to achieve

stable link, LED Control Register 0x13.2 should be 0.

The default CRC and IE Retry Forced Link is that after five

link drops due to increase error rate, the link will be forced

at the highest advertised speed. If during the link retry

stage that the link partner drops the link or the CAT5 cable

is unplugged, the retry counter will reload the retry count

with the default value of five. Note that the retry may take

forever to achieve a forced link when link partner drops the

link or CAT5 cable is unplugged.

3.3.4 Master/Slave Resolution

If 1000BASE-T mode is selected during the priority resolu-

tion, the second goal of Auto-Negotiation is to resolve Mas-

ter/Slave configuration. The Master mode priority is given

to the device that supports multiport nodes, such as

switches and repeaters. Single node devices such as DTE

or NIC card takes lower Master mode priority.

MULTI_EN is a strapping option for advertising the Multi-

node functionality. (Table 36) In the case when both PHYs

advertise the same option, the Master/Slave resolution is

Table 33. Speed/Duplex Selection, AN_EN = 1

DUP

Speed[1] Speed[0]

Comments

1000/100/10 HDX

1000/100 HDX

1000 HDX

1000/10 HDX

1000/100/10 FDX + HDX

1000/100 FDX + HDX

1000 FDX + HDX

1000/10 FDX + HDX

Table 34. LED Control Reg 0x13, Reg 0x1C0.3 = 1

Bit 2, AN Bit 1, CRC Bit 0, IE

Comments

No Speed Fallback (SF)

SF on idle error

SF on CRC error

SF on idle and CRC

SF on failing AN

SF on AN and IE

SF on AN and CRC

SF on AN, CRC, and IE

Table 35. LED Control Reg 0x13, Reg 0x1C0.3 = 0

Bit 2, AN Bit 1, CRC

Bit 0, IE

Comments

No Retry Forced Link

(RFL)

RFL on idle error

RFL on CRC error

RFL on idle and CRC

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