一、LAN8720A概述

1. 简介

LAN8720A/LAN8720Aiis a low power variableI/O电压的10/100M PHY收发器,符合IEEE 802.3-2005标准,支持通过RMII接口与以太网MAC通信.

LAN8720A/LAN8720AiImplement auto-negotiation,The best possible speed and duplex mode of operation is automatically determined.HP Auto-MDIXSupport allows the use of direct connect or crossover LAN cables.

LAN8720A/LAN8720Ai既支持IEEE 802.3-2005标准,It also supports vendor-specific registration functions.但是,Operations do not require access to registers.The initial configuration can be passed“配置带”Configuration pin selection as described in . Register-selectable configuration options can be used to further define the functionality of the transceiver.

2. LAN8720A典型应用

3. LAN8720A内部框图

4. LAN8720A引脚说明

PHY芯片使用的是LAN8720A,引脚图如下：

The classification and functions of pins are as follows：

其中RMII引脚只有7条数据线,相比MII有16条数据线,非常方便：

二、LAN8720A功能描述

1. Serial Management Interface（SMI）

SMIThe interface is used to control the device and get its state.

该接口支持802.3标准的第22the required registers0到6,as well as allowed by the specification“特定于供应商”的寄存器16到31,Unsupported register(例如7到15)will be read as hexadecimal“FFFF”.

SMI接口提供了2条信号线：MDIO和MDC.

• MDC信号：The controller is managed by the site(SMC)provided aperiodic clock,The minimum edge spacing is 160ns,There is no maximum interval
• MDIO信号：is a bidirectional dataSMI输入/输出信号,接收控制器SMC的串行数据(命令),并向SMC发送串行数据(状态)

读数据的时序：

写数据的时序：

2. PHY地址

PHY地址取决于PHYADDR引脚,This value is read at power-up,and stored in the register18里面,So it can also be configured by software.

3. 寄存器描述

其中寄存器0和寄存器1It is a general-purpose register specified by the standard.

寄存器2用来标识PHY ID：

寄存器3用来标识PHY ID：

三、使用uboot测试

uboot中提供了mii命令访问mdio总线：

（1）View currently available devices

mii device

（2）列出当前MII PHY信息

mii info

（3）读取PHY芯片寄存器