I'm currently working on a project of a testing module that requires three Ethernet ports:

  • one for network connection
  • two for external hardware (one of which is a device being tested)

The testing module uses an AM3352 SoM as a main controller and supports two MII interfaces. So I had to use W5500 (SPI interface) as a third Ethernet module instead of LAN8710A-EZC.

Question: the W5500 does not have PHYAD pins, and I am not sure if that's OK for my project... Is there a way to set physical address for this device, and does it need that at all? Or do I have to use an external PHY device to connect to the W5500?

  • \$\begingroup\$ PHY address is only relevant for MDIO bus. It has nothing to do with anything else. It's not part of Ethernet. \$\endgroup\$ Feb 9, 2023 at 13:16

2 Answers 2


That chip is a TCP/IP microcontroller with embedded PHY. You don't talk to the PHY directly, the microcontroller does. The SPI inferace you talk with the MCU has no concept of PHY address.

  • \$\begingroup\$ Ok. Can this chip be used with other Ethernets that include Phy addressing? Won't there be any indefinite addressing or whatsoever? I apologize if my question is silly, just trying to learn how to use the devices correctly. \$\endgroup\$ Feb 9, 2023 at 8:30
  • 1
    \$\begingroup\$ You are focusing on wrong detail. The PHY addressing is irrelevant to you, because you can think the Wiznet part as MCU and PHY bolted together. The MCU communicates with PHY in any way it wants and that is not relevant to you or Ethernet. You communicate to Wiznet MCU via SPI. PHY addressing is only relevant between a MCU and PHY, if you use the management interface, where the PHY addresses are used. You have no access to Wiznet PHY management interface, you don't need it. \$\endgroup\$
    – Justme
    Feb 9, 2023 at 10:12

The "PHY address" you refer to is an MDIO bus address. MDIO is a management interface between a MAC and one or more PHYs. In the case of the W5500, the MAC and PHY are integrated in the chip. Refer to the W5500 block diagram (green lines added by me):

enter image description here

So there's no need for an external management interface, or for PHYAD pins.

  • \$\begingroup\$ Thank you for your answer! What if multiple W5500 or a mixture of W5500 and LAN8700/LAN8710 are used in one board? Will there be any sort of conflict between those devices? \$\endgroup\$ Feb 9, 2023 at 8:48
  • \$\begingroup\$ No. You might be confusing MDIO addresses with MAC addresses. These are completely different and unrelated. MDIO addresses never appear on the Ethernet link or to other MACs/PHYs (except other PHYs that share the same MDIO bus... but you have no MDIO bus). \$\endgroup\$
    – TypeIA
    Feb 9, 2023 at 8:51

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