AL2100-DS00-R datasheet(19/52 Pages) BOARDCOM

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Preliminary Data Sheet

AL2100

11/11/02

Broa d c om Co rp o r a ti o n

Document

AL2100-DS01-405-R

100Base-Twisted Pair PHY

Page 11

POWER SOURCE

A single 2.5 V is supplied for all digital and analog operations.

100BASE-TWISTED PAIR PHY

GENERAL DESCRIPTION

The twisted pair PHY performs all of the physical layer interface functions for 100Base-TX full or half-duplex on CAT5 twisted

pair cable. The 100Base-TX PHY performs encoder/decoder, link monitor, auto-negotiation selection, adaptive equalization,

clock/data recovery, baseline wander correction, multimode transmitter, scrambler/descrambler, far-end fault (FEF), and

auto-MDI/MDIX. It is fully compliant with the IEEE 802.3 and 803.3u standards.

ENCODER/DECODER

In 100Base-TX mode, the AL2100 transmits and receives data streams on twisted pair. When the MII transmit enable is

asserted, nibble wide (4-bit) data from the transmit data pins is encoded into 5-bit code groups, and inserted into the transmit

data stream. The 4B5B encoding is shown in the 4B/5B CODE-GROUP table. The transmit packet is encapsulated by

replacing the first two nibbles of preamble with a start-of-stream delimiter (J/K codes), and appending an end-of-stream

delimiter (T/R codes) to the end of packet. When the MII transmit error input is asserted during a packet, the error code group

(H) is sent in place of the corresponding data code group. The transmitter repeatedly sends the idle code group between

packets.

In 100Base-TX mode, the encode data stream is scrambled by a stream cipher block, and serialized and encoded into the

MLT3 signal level. A multimode transmit DAC (digital to analog converter) is used to drive the MLT3 data onto twisted pair

cable. Following are baseline wander correction, adaptive equalization, and clock/data recovery in 100Base-TX mode. The

receive data stream is converted from MLT3 to serial NRZ data. The NRZ data is descrambled by the stream cipher block,

and deserialized and aligned into 5-bit code groups.

LINK MONITOR

In 100Base-TX mode, receive signal energy is detected by monitoring the receive pair for transitions in the signal level. The

signal levels are qualified using squelch detect circuits. When no signal, or a certain valid signal, is detected on the receive

pair for a minimum period of time, the link monitor enters the link-pass state, and the transmit and receive functions are

enabled.

AUTO-NEGOTIATION/AUTO-NEGOTIATION SELECTION

Auto-negotiation selection is on the 100Base-T twisted-pair PHY only; it is not operating in 100Base-Fiber PHY.

In 100Base-TX mode, auto-negotiation can be enabled or disabled by hardware or software control. When the auto-

negotiation function is enabled, the 100Base-TX PHY automatically chooses its mode of operation by advertising its abilities,

and comparing them with those received from its link partner. The 100Base-TX PHY can be configured to advertise as

100Base-TX full-duplex or 100BaseTX half-duplex.

The default auto-negotiation mode is configured via a reset read value of LED3/ANEN, LED2/DUPLEX. The SPD100 signal

is always defaulted to 1. When the SPD100 is set to 0, it is undefined, and the result is unexpected.

AL2100-DS00-R Datasheet(PDF) 19 Page - Broadcom Corporation.

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