LAN8808D datasheet(31/80 Pages) MICROCHIP

31 / 80 page

LAN8808D

DS00005833C-page 31

The auto-negotiation link-up process is shown in Figure 5-1.

For 1000BASE-T mode, auto-negotiation is required and always used to establish a link. During 1000BASE-T auto-

negotiation, the master and slave configuration is first resolved between link partners. Then the link is established with

the highest common capabilities between link partners.

Auto-negotiation is enabled by default after power-up or hardware reset. After that, auto-negotiation can be enabled or

disabled through the Basic Control register, bit[12]. If auto-negotiation is disabled, the speed is set by the Basic Control

If the speed is changed on the fly, the link goes down and either auto-negotiation and parallel detection initiate until a

common speed between the device and its link partner is re-established for a link.

If the link is already established and there is no change of speed on the fly, the changes (for example, duplex and pause

capabilities) will not take effect unless either auto-negotiation is restarted through the Basic Control register, bit[9] or a

link-down to link-up transition occurs (that is, disconnecting and reconnecting the cable).

After auto-negotiation is completed, the link status is updated in the Basic Status register, bit[2], and the link partner

capabilities are updated in Registers 5h, 6h, 8h, and Ah.

The auto-negotiation finite state machines use interval timers to manage the auto-negotiation process. The duration of

these timers under normal operating conditions is summarized in Table 5-2.

FIGURE 5-1:

AUTO-NEGOTIATION FLOW CHART

START AUTO-NEGOTIATION

FORCE LINK SETTING

LISTEN FOR 10BASE-T

LINK PULSES

LISTEN FOR 100BASE-TX

IDLES

ATTEMPT AUTO-

NEGOTIATION

LINK MODE SET

BYPASS AUTO-NEGOTIATION

AND SET LINK MODE

LINK MODE SET?

PARALLEL

OPERATION

YES

JOIN FLOW

LAN8808D Datasheet(PDF) 31 Page - Microchip Technology