LAN8720AI datasheet(17/79 Pages) SMSC

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Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support

Datasheet

SMSC LAN8720A/LAN8720Ai

Revision 1.4 (08-23-12)

DATASHEET

Chapter 3 Functional Description

This chapter provides functional descriptions of the various device features. These features have been

categorized into the following sections:

Transceiver

Auto-negotiation

HP Auto-MDIX Support

MAC Interface

Serial Management Interface (SMI)

Interrupt Management

Configuration Straps

Miscellaneous Functions

Application Diagrams

3.1

Transceiver

3.1.1

100BASE-TX Transmit

The 100BASE-TX transmit data path is shown in Figure 3.1. Each major block is explained in the

following subsections.

3.1.1.1

100BASE-TX Transmit Data Across the RMII Interface

The MAC controller drives the transmit data onto the TXD bus and asserts TXEN to indicate valid data.

The data is latched by the transceiver’s RMII block on the rising edge of REF_CLK. The data is in the

form of 2-bit wide 50MHz data.

Figure 3.1 100BASE-TX Transmit Data Path

MAC

Driver

MLT-3

Converter

NRZI

Converter

4B/5B

Encoder

CAT-5

RJ45

25MHz by

5 bits

NRZI

MLT-3

Scrambler

and PISO

RMII

25MHz

by 4 bits

Ext Ref_CLK

PLL

RMII 50Mhz by 2 bits

MLT-3

Magnetics

125 Mbps Serial

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