5228-DS05-R datasheet(14/100 Pages) BOARDCOM

14 / 100 page

BCM5228

Data Sheet

7/12/04

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

Page 2

Link Monitor

Document

5228-DS09-405-R

Following baseline wander correction, adaptive equalization, and clock recovery in TX mode, the receive data stream is

converted from MLT3 to serial NRZI data. The NRZI data is descrambled by the stream cipher block and then deserialized

and aligned into 5-bit code groups.

In FX mode, the receive data stream differential PECL levels are sampled from the fiber-optic receiver. Baseline wander

correction, adaptive equalization, and stream cipher descrambling functions are bypassed, and NRZI decoding is used

instead of MLT3.

The 5-bit code groups are decoded into 4-bit data nibbles, as shown in Table 1 on page 4. 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 RMII/SMII receive data pins. When an invalid code group is detected in the data stream, the BCM5228

asserts the RMII/SMII RXER signal. The chip also asserts RXER for several other error conditions that improperly terminate

the data stream. While RXER is asserted, the receive data pins are driven with a 01 for an invalid data reception and a 10

for a false carrier.

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

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

LINK MONITOR

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

Signal levels are qualified using squelch detect circuits. When no signal or certain invalid signals are detected on the receive

pair, the link monitor enters and remains in the Link Fail state where only idle codes are transmitted. When a 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.

In 100BASE-FX mode, the external fiber-optic receiver performs the signal energy detection function and communicates this

information directly to the BCM5228 through the differential SD± pins.

In 10BASE-T mode, a link-pulse detection circuit constantly monitors the RD± pins for the presence of valid link pulses.

CARRIER SENSE

In DTE mode, the carrier sense and receive data valid signals are multiplexed on the same pin. The carrier sense is asserted

asynchronously on the CRS_DV pin as soon as valid activity is detected in the receive data stream. Loss of carrier results

in the deassertion of CRS_DV synchronous to the cycle of REF_CLK that presents the first di-bit of a nibble onto RXD. If the

PHY has additional bits to be presented on RXD following the initial deassertion of CRS_DV, the PHY asserts CRS_DV on

cycles of REF_CLK that present the second di-bit of each nibble, and deasserts CRS_DV on cycles of REF_CLK that

present the first di-bit of each nibble. If carrier sense is asserted and a valid SSD is not detected immediately, RXER is

asserted. A value of 2h (2 hex) is driven on the receive data pins to indicate false carrier sense.

In 10BASE-T mode, carrier sense is asserted asynchronously on the CRS pin when valid preamble activity is detected on

the RD± input pins.

5228-DS05-R Folha de dados(PDF) 14 Page - Broadcom Corporation.