LAN8808D datasheet(30/80 Pages) MICROCHIP

30 / 80 page

LAN8808D

DS00005833C-page 30

Auto-MDIX detection is enabled in the device by default.

Auto-MDIX can be disabled by setting the swapoff bit in the Digital Debug Control 1 register. The MDI/MDI-X mode may

then be manually selected by the mdi_set bit in the Digital Debug Control 1 register.

The Auto-MDIX status bits are located in the Digital AX/AN Status register.

An isolation transformer with symmetrical transmit and receive data paths is recommended to support Auto MDI/MDI-X.

5.4

Alignment and Polarity Detection/Correction

In 1000BASE-T mode, the device supports 50 ns ±10 ns difference in propagation delay between pairs of channels in

accordance with the IEEE 802.3 standard, and automatically corrects the data skew so the corrected four pairs of data

symbols are synchronized.

Additionally, the device detects and corrects polarity errors on all MDI pairs, a useful capability that exceeds the require-

ments of the standard. Polarity detection and correction applies to 10BASE-T and 1000BASE-T and is not required for

100BASE-TX.

5.5

Wave Shaping, Slew-Rate Control, and Partial Response

In communication systems, signal transmission encoding methods are used to provide the noise-shaping feature and

to minimize distortion and error in the transmission channel.

• For 1000BASE-T, a special partial-response signaling method is used to provide the band-limiting feature for the

transmission path.

• For 100BASE-TX, a simple slew-rate control method is used to minimize EMI.

• For 10BASE-T, pre-emphasis is used to extend the signal quality through the cable.

5.6

Auto-Negotiation

The device conforms to the auto-negotiation protocol, defined in Clause 28 of the IEEE 802.3 Specification [1].

Auto-negotiation allows UTP link partners to select the highest common mode of operation.

During auto-negotiation, link partners advertise capabilities across the UTP link to each other, and then compare 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 operating mode.

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

• Priority 1: 1000BASE-T, full-duplex

• Priority 2: 1000BASE-T, half-duplex (Note 5-2)

• Priority 3: 100BASE-TX, full-duplex

• Priority 4: 100BASE-TX, half-duplex

• Priority 5: 10BASE-T, full-duplex

• Priority 6: 10BASE-T, half-duplex

Note 5-2

The device does not support 1000BASE-T, half-duplex and may not be enabled to advertise such.

If auto-negotiation is not supported or the device’s link partner is forced to bypass auto-negotiation for 10BASE-T and

100BASE-TX modes, the device sets its operating mode by observing the input signal at its receiver. This is known as

parallel detection, and allows the device to establish a link by listening for a fixed signal protocol in the absence of the

auto-negotiation advertisement protocol.

LAN8808D Datasheet(PDF) 30 Page - Microchip Technology

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