Preliminary Data Sheet

AC101L

8/9/04

B roa dcom Co rpo rat ion

Document

AC101L-DS06-R

FEF (Far-End Fault)

Page 5

Auto-negotiation provides the mechanism to inform the link partner that a remote fault has occurred. Auto-negotiation is

disabled, however, in the 100BASE-FX applications. An alternative in-band signaling function (FEFI) is used to signal a

remote fault condition.

FEFI is a stream of 84 consecutive ones followed by one logic zero. This pattern is repeated three times.

An FEFI signal is given under three conditions:

•

When no activity is received from the link partner.

•

When the clock recovery circuit detects a signal error or PLL lock error.

•

When a management entity sets the Transmit Far-End Fault bit.

The FEFI mechanism is enabled by default in the 100BASE-FX mode and disabled in 100BASE-TX or 10BASE-T modes.

The register setting can be changed by software after reset.

In 100BASE-TX mode, the PHY transmit function converts synchronous 4-bit data nibbles from the MII to a pair of 125-Mbps

differential serial data streams. The serial data are transmitted over network twisted-pair cables via an isolation transformer.

Data conversion includes 4B/5B encoding, scrambling, parallel-to-serial, NRZ to NRZI, and MLT3 encoding. The entire

operation is synchronous to the 25-MHz and 125-MHz clocks. Both clocks are generated by an on-chip PLL clock

synthesizer that is locked on to an external 25-MHz clock source.

In 100BASE-FX, the transmit driver does not perform filtering; it utilizes a current drive output that is well balanced and

produces a low noise PECL signal. PECL voltage levels are produced with resistive terminations.

In 10BASE-T mode, if the MII interface is used, parallel-to-serial logic is used to convert the 4-bit data into the serial stream

through the output wave shaping driver. The wave shaper reduces any EMI emission by filtering out the harmonics, therefore

eliminating the need for an external filter.

This feature is able to detect the required cable connection type (straight-through or crossed-over) and make correction

automatically.