There are two versions of KSZ8873: RLL and MLL (also FLL, but that is MLL with fiber ports). RLL uses reduced media-independent interface (RMI) and MLL uses a media-independent interface (MII) in port 3. MII has two modes: MAC and PHY.

The PHY mode needs to be matched between the switch and MAC controller. Normally, the MAC controller is connected to the switch, so PHY MII mode is the default. When the switch is connected directly to another switch, then one of them has to be in MAC MII mode. The default 0xA6 register setting of 0x13 just means port 3 is running in RMII mode and the other PHY ports are using copper (or a regular Ethernet jack). The MAC/PHY MII setting does not apply to RMII.

For more information, visit the KSZ8873 product page.

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