The LAN8650/1 combines a Media Access Controller (MAC) and an Ethernet PHY to enable low‑cost microcontrollers, including those without an onboard MAC, to access 10BASE‑T1S networks. The common standard Serial Peripheral Interface (SPI) of the LAN8650/1 allows interfacing with nearly any microcontroller, so that the transfer of Ethernet packets and LAN8650/1 control/status commands are performed over a single, serial interface. SPI also requires only 4 pins, enabling a simpler hardware interface with fewer pins than MII or RMII.

Ethernet packets are segmented and transferred over the serial interface according to the OPEN Alliance 10BASE‑T1x MAC‑PHY Serial Interface specification. The serial interface protocol can simultaneously transfer both transmit and receive packets between the station controller and the LAN8650/1. Packets are typically stored within the LAN8650/1 before being forwarded to either the station microcontroller or to the network. Alternatively, packets may be transferred in a cut-through mode for applications needing reduced latency.