LAN8820I datasheet(29/83 Pages) MICROCHIP

29 / 83 page

 2009-2015 Microchip Technology Inc.

DS00001871B-page 29

LAN8820/LAN8820I

The device also provides an advanced Auto Link Breaker feature (only for 1000BASE-T links). Using this feature, the

link can be taken down if the bit error rate (BER) exceeds the threshold defined in Link Break Threshold field of the Link

Control Register. The error counting occurs during the idle time for a period commensurate with the specified BER. The

Auto Link Breaker feature is enabled via the Link Break Enable bit of the Link Control Register.

3.9.4.3

100BASE-TX

For 100BASE-TX links, the device and its link partner begin transmitting idle symbols after completion of the auto-nego-

tiation process. Each side continues sending idle symbols whenever it has no data to transmit. The link is maintained

as long as valid idle symbols or data are received.

3.9.4.4

10BASE-T

For 10BASE-T links, the device and its link partner begin exchanging normal link pulses (NLPs) after completion of the

auto-negotiation process. The device transmits an NLP every 16ms and expects to receive an NLP every 8 to 24ms. A

link is maintained as long as NLPs are received.

3.9.4.5

Taking Down a Link

The device takes down an established link when the required conditions are no longer met. When a link is down, data

transmission stops. For 10BASE-T links, the link is taken down after NLPs are no longer received. For 100BASE-TX

and 1000BASE-T links, the link is taken down after valid idle codes are no longer received.

After a link is down, the device does the following:

• If auto-negotiation is enabled, the device re-enters the auto-negotiation phase and begins transmitting FLPs

• If auto-negotiation is not enabled, the device transmits NLPs in 10BASE-T mode, and MLT-3s in 100BASE-TX

mode.

3.9.5

SPEED OPTIMIZER

The Speed Optimize function is designed to resolve the issue of using auto-negotiation to establish a link on impaired

cable plants.

Examples of impaired cable plants for 1000BASE-T (Gigabit) connections include:

• Channel 2 twisted pair cable plant is broken

• Channel 3 twisted pair cable plant is broken

• Channel 2 and 3 twisted pair cable plants are broken

• Cable plant is too long

Examples of impaired cable plants for 100BASE-TX connections include:

• Cable plant is too long

• Using wrong cable plant (such as CAT-3)

The Speed Optimize function requires the MAC to support 1000/100/10 Mbps speeds, 1000/100 Mbps speeds, 1000/

10 Mbps or 100/10 Mbps speeds.

If a link fails to establish after the link partners go through auto-negotiation several times at the HCD (Highest Common

Denominator), the device advertises the next highest-allowable speed (as set in the Auto Negotiation Advertisement

When 1000BASE-T is advertised, the Speed Optimize function can change its advertised speed from 1000BASE-T to

100BASE-TX and from 100BASE-TX to 10BASE-T. When 100BASE-TX is advertised, the Speed Optimize function can

change its advertised speed from 100BASE-TX to 10BASE-T. If a previous link has used the Speed Optimize function

to establish a link, when the link goes down, the device begins advertising with all capable speeds.

The Speed Optimize function resets itself to advertise HCD/all speed capabilities after any of the following occurrences:

• Hardware reset

• Software reset

• While link partners exchange link pulses through the Speed Optimize process, the device does not receive link

pulses for a period of few seconds

• After an established link goes down

The Speed Optimize function is enabled via Speed Optimize Enable bit in the 10/100 Mode Control/Status Register.

When a link (with a speed slower than HCD) is being established through the Speed Optimize process, it is reported via

the Speed Optimize Status bit in the User Status 2 Register.

LAN8820I Datasheet(PDF) 29 Page - Microchip Technology

LAN8820I Datasheet(HTML) 29 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83

Datasheet Download

Link URL