PHY-dat

PHY (Physical Layer Transceiver)

In networking, a PHY is a hardware component responsible for the Physical Layer (Layer 1) of the OSI model, which deals with the electrical or optical signal transmission and reception. It's typically used in Ethernet systems to interface between the digital data from a MAC (Media Access Controller) and the physical medium, such as twisted-pair cables or fiber optics.

Key roles of a PHY:

  • Signal encoding/decoding: Converts digital data (from the MAC) into signals suitable for transmission over physical media (and vice versa).
  • Clock recovery: Extracts clock signals from incoming data streams.
  • Auto-negotiation: Determines connection parameters like speed (10/100/1000 Mbps) and duplex mode (full/half).
  • Media-dependent interfaces: Provides the electrical interface for the transmission medium, such as copper wires or fiber.

The PHY communicates with the MAC through standardized interfaces like RGMII, MII, or GMII.

RGMII (Reduced Gigabit Media Independent Interface)

RGMII is a standard interface used between a MAC and a PHY to support Gigabit Ethernet (1 Gbps) connectivity. It is a more compact and efficient version of GMII, reducing the number of data pins.

Features of RGMII:

  1. Reduced pin count: Uses only 12 data pins (compared to GMII's 24 pins) by transmitting data on both the rising and falling edges of the clock (DDR - Double Data Rate).
  2. Speed support: Capable of operating at 10 Mbps, 100 Mbps, and 1 Gbps.
  3. Signals in RGMII:
    • TX (Transmit) and RX (Receive) data signals
    • Clock signals for TX and RX
    • Control signals (TX_EN, RX_DV)

RGMII enables the MAC and PHY to communicate effectively while optimizing space and complexity.

MDIO (Management Data Input/Output)

The MDIO (Management Data Input/Output) interface is a two-wire protocol used for managing and configuring Ethernet PHYs. It allows the MAC (or a host controller) to:

  • Read status registers in the PHY.
  • Configure operating modes (e.g., speed, duplex, auto-negotiation settings).

MDIO Interface Components:

  • MDIO Signal: A bidirectional data line that transfers register addresses and data between the controller and the PHY.
  • MDC (Management Data Clock): A clock signal provided by the MAC or host to synchronize MDIO operations.

Using the MDIO interface, a host can control multiple PHY devices on the same bus by assigning unique addresses to each PHY.

Table of Contents