KSZ9021GN TR Micrel Inc, KSZ9021GN TR Datasheet - Page 20

• Manufacturer Part Number: KSZ9021GN TR
• Description: Specifications: Number of Drivers/Receivers: 8/8 ; Type: Transceiver ; Voltage - Supply: 3.135 V ~ 3.465 V ; Package / Case: 64-VFQFN Exposed Pad ; Packaging: Tape & Reel (TR) ; Protocol: Gigabit Ethernet ; Lead Free Status: Lead Free ; RoHS Stat
• Manufacturer: Micrel Inc

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
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M9999-091010-1.1