The ML6691 implements the upper portion of the physical layer for the Fast Ethernet 100BASE-T standard. Functions contained in the ML6691 include a 4B/5B encoder/ decoder, a Stream Cipher scrambler/descrambler, and collision detect. Additional functions of the ML6691 -- accessible through the two-wire MII management interface -- include full duplex operation, loopback, power down mode, and MII isolation.