LXT975B datasheet(24/74 Pages) INTEL

24 / 74 page

LXT974/LXT975 — Fast Ethernet 10/100 Quad Transceivers

Datasheet

Collision

The LXT974/975 asserts its collision signal, asynchronously to any clock, whenever the line state

is half-duplex and the transmitter and receiver are active at the same time. Table 14 summarizes the

conditions for assertion of carrier sense, collision, and data loopback signals.

2.2.2.2

MII Management Interface

The LXT974/975 supports the IEEE 802.3 MII Management Interface also known as the

Management Data Input/Output (MDIO) Interface. This interface allows upper-layer devices to

monitor and control the state of the LXT974/975. The MDIO interface consists of a physical

connection, a specific protocol that runs across the connection, and an internal set of addressable

registers. Some registers are required and their functions are defined by the IEEE 802.3

specification. Additional registers are allowed for expanded functionality. The LXT974/975 is

configured with both sets of registers.

The physical interface consists of a data line (MDIO) and clock line (MDC). Operation of this

interface is controlled by the MDDIS input pin. When MDDIS is High, the MDIO operates as a

read-only interface. When MDDIS is Low, both read and write are enabled. The timing for the

MDIO Interface is shown in Table 40 on page 61. The protocol is shown in Figure 8 and Figure 9

(read and write). The protocol allows one controller to communicate with up to eight LXT974/975

chips. Bits A4:2 of the 5-bit PHY address are assigned as the LXT974/975 address. Bits A1:0 are

assigned as port addresses 0 through 3. The LXT974/975 supports 12 internal registers per port (48

total), each of which is 16 bits wide.

Figure 7. Loopback Paths

Digital

Block

MII

Analog

Block

Driver

100TX

Loopback

100FX

Loopback

10T

Loopback

Table 14. Carrier Sense, Loopback, and Collision Conditions

Speed & Duplex Condition

Carrier Sense

Loopback

Collision

Full-Duplex at 10 Mbps or 100 Mbps

Receive Only

None

100 Mbps, Half-Duplex

Transmit or Receive

None

Transmit and Receive

10 Mbps, Half-Duplex, 19.11 = 0

Transmit or Receive

Yes

Transmit and Receive

10 Mbps, Half-Duplex, 19.11 = 1

Transmit or Receive

None

Transmit and Receive

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