KSZ9897R datasheet(21/196 Pages) MICROCHIP

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DS00002330E-page 21

KSZ9897R

4.1.7

AUTO-NEGOTIATION

The device conforms to the auto-negotiation protocol as described by IEEE 802.3. Auto-negotiation allows each port to

operate at either 10BASE-Te, 100BASE-TX or 1000BASE-T by allowing link partners to select the best common mode

of operation. During auto-negotiation, the link partners advertise capabilities across the link to each other and then com-

pare their own capabilities with those they received from their link partners. The highest speed and duplex setting that

is common to the two link partners is selected as the mode of operation. With parallel detection, the duplex will always

be half-duplex.

The following list shows the speed and duplex operation mode from highest to lowest priority.

• Priority 1: 1000BASE-T, full-duplex

• Priority 2: 1000BASE-T, half-duplex

• Priority 3: 100BASE-TX, full-duplex

• Priority 4: 100BASE-TX, half-duplex

• Priority 5: 10BASE-Te, full-duplex

• Priority 6: 10BASE-Te, half-duplex

If the KSZ9897R link partner doesn’t support auto-negotiation or is forced to bypass auto-negotiation for 10BASE-Te

and 100BASE-TX modes, the KSZ9897R port sets its operating speed by observing the signal at its receiver. This is

known as parallel detection, and allows the KSZ9897R to establish a link by listening for a fixed signal protocol in the

absence of the auto-negotiation advertisement protocol.

The auto-negotiation link-up process is shown in Figure 4-1.

FIGURE 4-1:

AUTO-NEGOTIATION AND PARALLEL OPERATION

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