Preliminary Data Sheet

AC101L

8/9/04

B roa dcom Co rpo rat ion

Document

AC101L-DS06-R

Functional Description

Page 1

Secti on 1: Fu nction al Descri p ti on

The AC101L is a single-chip, Fast Ethernet transceiver. It performs all of the physical layer interface functions for

100BASE-TX full-duplex or half-duplex on Category 5 twisted-pair cable, and 10BASE-T full-duplex or half-duplex on

Category 3 cable. It can be configured for 100BASE-FX full- or half-duplex transmission over fiber-optic cable when paired

with an external fiber-optic line driver and receiver.

The chip performs 4B5B, MLT3, NRZI, 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 can be connected to a MAC switch controller through the MII on one side and directly to the media on the

other side through a transformer for twisted-pair (TP) mode, or fiber-optic module for FX mode. It is fully compliant with the

IEEE 802.3 and 803.3u standards.

In 100BASE-TX and 100BASE-FX modes, the AC101L transmits and receives data stream on twisted-pair or fiber-optic

cable. When the MII transmit enable is asserted, nibble wide (4-bit) data from transmit data pins is encoded into 5-bit code

groups and inserted into transmit data stream. The 4B/5B encoding is shown in Section 6: “4B/5B Code Group” on page 26.

The transmit packet is encapsulated by replacing the first 2 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 sends

repeatedly the idle code group between packets.

In 100BASE-TX mode, the encode data stream is first scrambled by a stream cipher block and then serialized and encoded

into an MLT3 signal level. Second, a multimode transmit DAC (digital to analog converter) is used to drive the MLT3 data

onto twisted-pair cable. Following 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 are descrambled by the stream

cipher block and then deserialized and aligned into 5-bit code groups.

In 100BASE-FX mode, the scrambling function is bypassed and the data are NRZII-encoded. The multi mode transmit DAC

drives differential Positive ECL (PECL) levels to an external fiber-optic transmitter. Baseline wander correction, adaptive

equalization, 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. 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 are driven onto the MII receive

data pins. When an invalid code group or bad SSD is detected in the data stream, the AC101L asserts the MII RXER signal.

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

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

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 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.