LAN8720 – the possibility of integration

[Marcin_W]

Dear All,
The availability of the AR8035 chip is limited. The LAN8720 is easily available from global retail distributors. I got acquainted with “Ethernet compatible PHYs” but I found only information related to LAN8710. We are working on our own project and because of the price and availability LAN8720 is very attractive. Additionally, DEVBoard is available: https://www.waveshare.com/wiki/LAN8720_ETH_Board
which will be very helpful in testing.
Please help in the topics:
1)Opinion on the co-operation of the LAN8720 system with OSD335x-SM
2)Comments, recommendations
3)Maybe someone has experience in this area LAN8720+OSD335x-SM
Thank you.

[Erik Welsh]

First, be aware that the AR8035 is a 10/100/1000 Ethernet PHY, while the LAN8720 is a 10/100 Ethernet PHY.  The reason you find more information about the LAN8710 interfacing to the AM335x or OSD335x is due to the open hardware reference designs from BeagleBoard.org that use that device.  However, the LAN8720 should work as well.  It appears that the LAN8720 uses the same Linux driver as the LAN8710, but within Octavo, we do not have experience with the LAN8720 and the OSD335x family of devices.  The main thing to be aware of is that the LAN8720 uses RMII, so you need to make sure that the layout comprehends the clocking and timing requirements of RMII so that you don’t run into any issues.

[Marcin_W]

Thank you very much for help. I am looking for a LAN8720 connection scheme for OSD3358-512-ISM but I can not find one. The only scheme that seems to be useful is here : https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/791/1185.am335x_2D00_LAN8720A.png , but it still does not fully explain. I do not know how to connect ETHRXER (AM335). I do not know how to connect nINT / REFCLK from the LAN8720 module. There is a problem with the 50MHz clock. Can you help us in this matter. The 50MHz generator is on the LAN8720 ETH BOARD, if needed we can use it as a source for the RMII AM335X

[Marcin_W]

Thank you very much for help. I am looking for a LAN8720 connection scheme for OSD3358-512-ISM but I can not find one. The only scheme that seems to be useful is attached, but it still does not fully explain. I do not know how to connect ETHRXER (AM335). I do not know how to connect nINT / REFCLK from the LAN8720 module. There is a problem with the 50MHz clock. Can you help us in this matter. The 50MHz generator is on the LAN8720 ETH BOARD, if needed we can use it as a source for the RMII AM335X

Attachments:

1. 

   1185.am335x-LAN8720A.png
   

[Marcin_W]

I enclose my connection proposal.

Attachments:

1. 

   am335x-LAN8720A_ETH_BOARD_Proposal.png
   

[Erik Welsh]

Marcin,

Unfortunately, we do not have a reference design that uses the LAN8720.

Looking through your connection proposal, you will need to make a few minor adjustments.  If you look in the LAN8720 datasheet (http://ww1.microchip.com/downloads/en/devicedoc/00002165b.pdf), there are two connection schemes listed.  Figure 3.7 shows the connections when using an external 50MHz clock source.  In this case, nINT/REFCLKO is an interrupt and should go to a GPIO pin on the OSD335x device.  Additionally, you need to be careful in layout to make sure that the clock is balanced between the PHY and the OSD335x.  Figure 3.8 shows the connections when using a 25MHz crystal.  In this case, nINT/REFCLKO is used as a reference clock that should be sent to the OSD335x.

Figure 3.8 is what is shown in the first picture you attached from the reference design.  If you would like to use the 50 MHz oscillator, then you will need to remove R11 in your diagram and connect the nINT/REFCLKO to a different GPIO pin that you will specify as the Ethernet interrupt in your device tree.  Alternatively, you can change the 50MHz oscillator to a 25MHz crystal and use the connections from the reference design.

Regardless, you will need to add the appropriate pull up resistors (i.e. the 10K resistors in the reference design picture) in order to set all the strap pins.  Additionally, you will need to add the 1.5k pull up resistor the the MDIO connection per the Ethernet specification.  Also, it is a good idea to add the 33Ohm termination resistors to help with signal integrity on the interface.

Please let us know if you have any additional questions on this.

 

 

 

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