Intel Gigabit Ethernet Controllers Benutzerhandbuch

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The internal MII implementation for the Ethernet controller provides full IEEE 802.3 and IEEE 

802.3u compliant operation for 10Mb/s and 100Mb/s operation in conjunction with the onboard 

MII compliant PHY. 

The MII uses a clocked, nibble-wide (4-bit) data path in each direction. The clock rate for Fast 
Ethernet operation is 25 MHz with data transfer speed of 4 bits x 25 MHz = 100 Mb/s. For 

10 Mb/s operation the clock rate is 2.5 MHz and also uses the nibble-wide data path.

The Ethernet controller supports the IEEE 802.3 MII Management Interface also known as the 

Management Data Input/Output (MDI/O) Interface. This interface allows upper-layer devices to 
monitor and control the state of the PHY. 

For the 82546GB/EB, 82545GM/EM, 82541xx, 82540EP/EM, and 82547GI/EI, the MDI/O 

interface consists of an internal connection, a special protocol that runs across the connection, and 

an internal set of addressable registers. For the 82541xx and 82547GI/EI, the physical interface 
between the MAC and PHY is not available externally.

For the 82544GC/EI, the MDI/O interface consists of a physical connection, a special protocol that 

runs across the connection, and an internal set of addressable registers. The physical interface 

consists of a (B_MDIO) data line and a clock line (O_MDC).

•

O_MDC:
Management Data Clock, used by the PHY as a clock timing reference for information transfer 

on the B_MDI/O signal. The O_MDC is not a continuous signal and can be frozen by the 
Ethernet controller when no management data is transferred. The O_MDC signal has a 

maximum operating frequency of 2.5 MHz.

•

B_MDO:
Management Data I/O, a bidirectional data signal used to transfer control information and 

status between the Ethernet controller and the PHY (read and write PHY management 
registers). The B_MDO signal is sampled by the rising edge of the O_MDC signal.

Software can use MDI/O to read and write registers in a internal PHY by accessing the Ethernet 

controller’s MDIC register.

The 82546GB/EB and 82545GM/EM supports half-duplex and full-duplex 10/100 Mb/s mode. 

Half-duplex in 1000 Mb/s mode using either the Internal SerDes or GMII interface is NOT 
supported.

The 82544GC/EI, 82540EP/EM, 82541xx, and 82547GI/EI, support half-duplex and full-duplex 

10/100 Mb/s mode or 1000 MB/s mode. However, only full-duplex mode is supported when the 

 TBI interface option is used.

1.

MDIO/MDC Interface for the 82544GC/EI, 82540EP/EM, 82541xx, and 82547GI/EI.