5220-DS02-R datasheet(14/90 Pages) BOARDCOM

14 / 90 page

BCM5220

Preliminary Data Sheet

04/20/04

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

Page 2

Link Monitor

Document

5220-DS04-405-R

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 CAT 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 BCM5220 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 100BASE-X modes, carrier sense is asserted asynchronously on the CRS pin as soon as activity is detected in the receive

data stream. RXDV is asserted as soon as a valid Start-of-Stream Delimiter (SSD) is detected. Carrier sense and RXDV are

deasserted synchronously upon detection of a valid end of stream delimiter or two consecutive idle code groups in the

receive data stream. If carrier sense is asserted and a valid SSD is not detected immediately, then RXER is asserted in place

of RXDV. A value of 1110 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.

In half-duplex DTE mode, the BCM5220 asserts carrier sense while transmit enable is asserted and the link monitor is in the

Pass state. In full-duplex mode, CRS is only asserted for receive activity.

COLLISION DETECTION

In half-duplex mode, collision detect is asserted on the COL pin whenever carrier sense is asserted and transmission is in

progress.

5220-DS02-R Datasheet(PDF) 14 Page - Broadcom Corporation.