5238-DS03-405-R datasheet(9/76 Pages) BOARDCOM

9 / 76 page

Advance Data Sheet

BCM5238

1/31/03

Broa d c om Co rp o r a t i o n

Document

5238-DS03-405-R

Functional Description

Page 1

Secti on 1: Fu nction al Descri p ti on

OVERVIEW

The BCM5238 is a single-chip device containing eight independent Fast Ethernet transceivers. Each transceiver performs

all of the physical layer interface functions for 100BASE-TX full-duplex or half-duplex Ethernet on Category 5 twisted-pair

cable and 10BASE-T full-duplex or half-duplex Ethernet on Category 3, 4, or 5 cable.

The chip performs 4B5B, MLT3, NRZI, and Manchester encoding and decoding, clock and data recovery, stream cipher

scrambling/descrambling, digital adaptive equalization, line transmission, carrier sense and link integrity monitor,

auto-negotiation SMII and SSMII management functions. The BCM5238 may be connected to a MAC through the SMII or

SSMII on one side and connects directly to the network media on the other side through isolation transformers. The

BCM5238 is compliant with the IEEE 802.3 standard.

ENCODER/DECODER

The BCM5238 transmits and receives a continuous data stream on twisted pair. When the transmit enable is asserted, 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 Table 1. 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 the packet. The transmitter

repeatedly sends the idle code group between packets.

The encoded data stream is scrambled by a stream cipher block and then serialized and encoded into MLT3 signal levels.

A multimode transmit DAC is used to drive the MLT3 data onto the twisted pair cable.

Following adaptive equalization, and clock recovery, the receive data stream is converted from MLT3 to serial NRZ data.

The NRZ data is descrambled by the stream cipher block and then deserialized and aligned into 5-bit code groups.

The 5-bit code groups are decoded into 4-bit data nibbles, as shown in Table 1. The start of stream delimiter is replaced with

preamble nibbles and the end of stream delimiter and idle codes are replaced with all zeros. The decoded data is driven onto

the SMII receive data stream. When an invalid code group is detected in the data stream, the BCM5238 asserts the SMII

RXER signal in the receive data stream. The chip also asserts RXER for several other error conditions which improperly

terminate the data stream.

In 10BASE-T mode, Manchester encoding and decoding is performed on the data stream. The multimode transmit DAC

performs pre-equalization for 100 meters of Category 3 cable.

Table 1: 4B5B encoding

Name

4B Code

5B Code

Meaning

0000

11110

Data 0

0001

01001

Data 1

0010

10100

Data 2

0011

10101

Data 3

0100

01010

Data 4

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