Media Independent Interface - Reduced Media Independent Interface

Reduced Media Independent Interface

Reduced Media Independent Interface (RMII) is a standard which was developed to reduce the number of signals required to connect a PHY to a MAC. Four things were changed compared to the MII standard to achieve this:

  • The two clocks TXCLK and RXCLK are replaced by a single clock. This clock is an input to the PHY rather than an output, which allows the clock signal to be shared among all PHYs in a multiport device, such as a switch.
  • The clock frequency is doubled from 25 MHz to 50 MHz, while the data paths are narrowed to 2 bits rather than 4 bits.
  • RXDV and CRS signals are multiplexed to one signal.
  • The COL signal is removed.

These changes means that RMII uses about half the number of signals compared to MII. The high pin count of MII is more of a burden on microcontrollers with built-in MAC, FPGA's, multiport switches or repeaters, and PC motherboard chipsets than it is for a separate single port Ethernet MAC which partially explains why the older MII standard was more wasteful of pins.

Read more about this topic:  Media Independent Interface

Famous quotes containing the words reduced, media and/or independent:

    “There surely is a being who presides over the universe; and who, with infinite wisdom and power, has reduced the jarring elements into just order and proportion. Let speculative reasoners dispute, how far this beneficent being extends his care, and whether he prolongs our existence beyond the grave, in order to bestow on virtue its just reward, and render it fully triumphant.”
    —David Hume (1711–1776)

    “The media no longer ask those who know something ... to share that knowledge with the public. Instead they ask those who know nothing to represent the ignorance of the public and, in so doing, to legitimate it.”
    —Serge Daney (1944–1992)

    “The soul of me is very selfish. I have gone my way after a fashion that made me the center of the plan. And you who are so individual, who are so independent a spirit, whose soul is also a kingdom, have been so loyal, so forgiving, so self-sacrificing in your willingness to live my life. Nothing but love cold have accomplished so wonderful a thing.”
    —Woodrow Wilson (1856–1924)