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:

    “The Gettysburg speech is at once the shortest and the most famous oration in American history. Put beside it, all the whoopings of the Websters, Sumners and Everetts seem gaudy and silly. It is eloquence brought to a pellucid and almost gem-like perfection—the highest emotion reduced to a few poetical phrases.”
    —H.L. (Henry Lewis)

    “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 ex-Presidential situation has its advantages, but with them are certain drawbacks. The correspondence is large. The meritorious demands on one are large. More independent out than in place, but still something of the bondage of the place that was willingly left. On the whole, however, I find many reasons to be content.”
    —Rutherford Birchard Hayes (1822–1893)