LXT971ABC datasheet(45/90 Pages) INTEL

45 / 90 page

LXT971A 3.3V Dual-Speed Fast Ethernet Transceiver

Datasheet

Document #: 249414

Revision #: 002

Rev. Date: August 7, 2002

• Register bits 17.14 and 17.9 can be used to determine the link operating conditions (speed and

duplex).

3.9.1.1

Monitoring Next Page Exchange

The LXT971A offers an Alternate Next Page mode to simplify the next page exchange process.

Normally, Register bit 6.1 (Page Received) remains set until read. When Alternate Next Page mode

is enabled Register bit 6.1 is automatically cleared whenever a new negotiation process takes place.

This prevents the user from reading an old value in 6.1 and assuming that Registers 5 and 8

(Partner Ability) contain valid information. Additionally, the LXT971A uses Register bit 6.5 to

indicate when the current received page is the base page. This information is useful for recognizing

when next pages must be resent due to a new negotiation process starting. Register bits 6.1 and 6.5

are cleared when read.

3.9.2

LED Functions

The LXT971A incorporates three direct LED drivers. On power up all the drivers are asserted for

approximately 1 second after reset de-asserts. Each LED driver can be programmed using the LED

Configuration Register (refer to Table 56 on page 85) to indicate one of the following conditions:

• Operating Speed

• Transmit Activity

• Receive Activity

• Collision Condition

• Link Status

• Duplex Mode

The LED drivers can also be programmed to display various combined status conditions. For

example, setting Register bits 20.15:12 = 1101 produces the following combination of Link and

Activity indications:

• If Link is down LED is off.

• If Link is up LED is on.

• If Link is up and activity is detected, the LED blinks at the stretch interval selected by Register

bits 20.3:2 and continues to blink as long as activity is present.

The LED driver pins also provide initial configuration settings. The LED pins are sensitive to

polarity and automatically pull up or pull down to configure for either open drain or open collector

circuits (10 mA Max current rating) as required by the hardware configuration. Refer to the

discussion of “Hardware Configuration Settings” on page 30 for details.

3.9.2.1

LED Pulse Stretching

The LED Configuration Register also provides optional LED pulse stretching to 30, 60, or 100 ms.

The pulse stretch time is further extended if the event occurs again during this pulse stretch period.

When an event such as receiving a packet occurs it is edge detected and it starts the stretch timer.

The LED driver remains asserted until the stretch timer expires. If another event occurs before the

stretch timer expires then the stretch timer is reset and the stretch time is extended.

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