LXT975B datasheet(27/74 Pages) INTEL

27 / 74 page

Fast Ethernet 10/100 Quad Transceivers — LXT974/LXT975

Datasheet

2.3

Initialization

At power-up or reset, the LXT974/975 performs the initialization as shown in Figure 11. Control

mode selection is provided via the MDDIS pin as shown in Table 18. When MDDIS (pin 100) is

High, the LXT974/975 operates in Manual Control Mode. When MDDIS is Low, the LXT974/975

operates in MDIO Control Mode.

2.3.1

MDIO Control Mode

In the MDIO Control Mode, the LXT974/975 uses the Hardware Control Interface to set up initial

(default) values of the MDIO registers. The MDIO Register set for the LXT974/975 is described in

Table 44 through Table 55. Specific bits in the registers are referenced using an “X.Y” notation,

where X is the register number (0-6 or 16-20) and Y is the bit number (0-15). Once initial values

are set, bit control reverts to the MDIO interface.

2.3.2

Manual Control Mode

In the Manual Control Mode, LXT974/975 disables direct write operations to the MDIO registers

via the MDIO interface. The Hardware Control Interface is continuously monitored and the MDIO

registers are updated accordingly.

Table 17. Configuring the LXT974/975 with Auto-Negotiation Disabled

Desired Configuration1,2

Pin Settings

MDIO Registers

SD/TPn

per port

CFG_2

global

CFG_0

global

FDE

global

FDE_FX

0.8

0.13

19.2

Per Port (Fiber) Configuration

Fiber operation can be forced per port via SD/TPn pins when auto-negotiation is enabled. Per-port settings override the global

pin settings.

100FX Full-Duplex

Operation.

High or

PECL3

Ignored

High

100FX Half-Duplex

Operation.

High or

PECL3

Ignored

Low

Global (Twisted-Pair) Configuration5

Force 100TX Full-Duplex

Operation on all ports.4

Low

High

Ignored

Force 100TX Half-Duplex

Operation on all ports.4

Low

High

Low

Ignored

Force 10T Full-Duplex

Operation on all ports.

Low

High

Ignored

Force 10T Half-Duplex

Operation on all ports.

Low

Ignored

1. Refer to Table 15 for basic configurations.

2. Refer to Table 16 for Hardware Control Interface functions advertised when auto-negotiation is enabled.

3. When SD/TPn is set High or to PECL levels, auto-negotiation is disabled and FDE_FX determines the duplex mode of the

port.

4. CFG_2, CFG_0, and SD/TPn must all be set for 100TX operation.

5. Fiber configuration must be selected on a per-port basis.

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