Chapter · Ethernet
The cable and the chips
How a link comes up, the MAC and the PHY and the seven wires between them, and how a frame reaches an IP address.
- 06How the link comes up4 minBefore a link light comes on, the two ends of a cable advertise what they can do and pick the best mode they share. A link light proves the cable and the PHYs, and nothing above them.
- 07The MAC, the PHY and their wires5 minThe MAC builds and checks frames, the PHY drives the cable, and RMII joins them with seven signals timed by one 50 MHz clock. Two more wires, MDC and MDIO, let the MAC read the PHY's registers.
- 08From frames to an IP address4 minA link that is up has no IP address yet. On an ESP32 the driver hands frames to lwIP through esp_netif, and code should wait for the got-IP event, not the link-up event, before it talks.
Start at 06 and read down — the order is the order things get easier in. Or take the one with your part in it; every article stands on its own, and links back to whatever it needs.