KSZ9021GN Ver la hoja de datos (PDF) - Micrel

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KSZ9021GN

Gigabit Ethernet Transceiver with GMII / MII Support

Micrel 

Micrel, Inc.

KSZ9021GN

Figure 3. Auto-Negotiation Flow Chart

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, and then the link is established

with the highest common capabilities between link partners.

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

or disabled through register 0 bit 12. If auto-negotiation is disabled, the speed is set by register 0 bits 6 and 13, and the

duplex is set by register 0 bit 8.

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

common speed between KSZ9021GN and its link partner is re-established for a link.

If link is already established and there is no change of speed on the fly, then the changes will not take effect unless

either auto-negotiation is restarted through register 0 bit 9, or a link down to link up transition occurs (i.e., disconnecting

and reconnecting the cable).

After auto-negotiation is completed, the link status is updated in register 1 and the link partner capabilities are updated

in registers 5, 6, and 10.

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

of these timers under normal operating conditions are summarized in the following table.

September 2010

20

M9999-091010-1.1

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