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:

    “Narrowed-down by her early editors and anthologists, reduced to quaintness or spinsterish oddity by many of her commentators, sentimentalized, fallen-in-love with like some gnomic Garbo, still unread in the breadth and depth of her full range of work, she was, and is, a wonder to me when I try to imagine myself into that mind.”
    —Adrienne Rich (b. 1929)

    “The question confronting the Church today is not any longer whether the man in the street can grasp a religious message, but how to employ the communications media so as to let him have the full impact of the Gospel message.”
    —Pope John Paul II (b. 1920)

    “I have defeated them all.... I was left with some money to battle with the world when quite young, and at the present time have much to feel proud of.... The Lord gave me talent, and I know I have done good with it.... For my brains have made me quite independent and without the help of any man.”
    —Harriet A. Brown, U.S. inventor and educator. As quoted in Feminine Ingenuity, ch. 8, by Anne L. MacDonald (1992)