[datasheet] interpretation of phy lan8720 network chip

Let's talk about the advantages of this chip first , Electric power 、 Industry 、 Medical electronics have had this PHY Chip applications , Why so popular , There must be a reason ;

1、 The package size is very small ,24-pin QFN,package (4 x 4 x 0.85mm height);

2、10/100M The adaptive , accord with IEEE802.3/802.3u;

3、 The price in 8 yuan ;

4、 Can support RMII Interface , External grounding 25M Crystal oscillator , But the internal frequency doubling is 50MHZ, Provide to MCU Make reference clock ;

System diagram , There is crystal oscillator signal 、RMII Media interface 、MDIO Register read / write interface 、LED;

Architectural Overview

This chip does not support MII Interface .

RMII and MII All media interfaces , What are the differences and connections ？

MII Called media independent interface ,16 Root line ,TX_CLK and RX_CLK The clock is 25MHZ,PHY External grounding 25M Crystal oscillator , such as ：100M The bandwidth of the , The rate of each data line is 25M, So we need 4 Send and receive through a data line .

RMII To simplify the media independent interface ,7 Root line , The transceiver clock is increased to 50Mhz, Again 100M bandwidth , It only needs two data cables , But be careful ,MAC And PHY The clock source must be synchronized .

LED It is also possible to define functions through programming ;

The above figure is the application block diagram , Pay attention to the parameters of network tap when selecting hardware ;

Software debugging skills ：

If appear PHY Debugging failure , The following points need to be checked ;

1、 First measure whether the external voltage of the chip is normal ,3.3V Power Supply ;

2、 Whether the external crystal oscillator vibrates , Observe whether the active crystal oscillator pins are placed correctly , measurement REF_CLK 50MHZ;

3、 Network tap parameter check ;

4、 All of the above are true , Print PHY Register values , Check the corresponding status according to the manual ;

Pay attention to WeChat public number , reply “LAN8720”, The chip manual is free to download ;