ST70134 - ST70135A

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GENERAL DESCRIPTION

The ADSL modem chip set with ATM interface

provides all the active functions required to build a

complete ATM-based ADSL modem from line

interface to ATM UTOPIA bus. The chip set

employs

Discrete

MultiTone

modulation

as

specified in ANSI T1.413.

The chip set operates at CPE end of the loop

(ATU-R mode).

Reed-Solomon forward error

correction plus Trellis coding with or without

interleaving in internal interleaving RAM provides

maximum noise immunity (see Figure 3).

Interleaving

is

optional

and

can

be

used

simultaneously on a slow channel (e.g., for data or

control info) while a fast channel (e.g., video)

operates without interleaving. ICs include rate

adaptation capabilities during show time.

In transmit direction the chip set allows to select

an attenuation of the signal in case of short loops

or large echo (politeness). In receive direction the

chip set can optionally control an external

multiplexer to select an external attenuation of the

signal in case of short loops, and provide a 2-bit

output external gain control.

ASCOT chip set

ASCOT is a two-chip ADSL modem transceiver.

STMicroelectronics

provides

the

necessary

software for transceiver’s external controller.

ASCOT can easily be hooked up with ATM

systems through the built-in UTOPIA level 2/1

interface. That allows ATM traffic to be carried at

up to 8Mbit/s downstream and 1Mbit/s upstream,

over a very plain and widespread twisted pair.

ASCOT is intended for use at ATU-R end.

The modem control software can be compiled as

C++ code, independently on the processor used.

The driver can be interfaced to any external real

time operating system.

These pages block diagrams show the main

functions built-in in ST70134 and ST70135A.

ASCOT chip set supports three different rate

adaptation modes: fixed rate adaptation mode,

fixed with capability to boost within fixed range,

dynamic rate adaptation during show time.

Modem’s performances are set by the following

parameters: Rate adaptation mode, Downstream

and Upstream bit rate for both latency paths,

Noise margins (min, max and target typically at

10E-7 BER without RS, interleaving and trellis),

Maximum power spectral density for downstream,

Maximum power for both up and downstream,

Carrier

mask

(which

tones

are

disabled),

maximum interleaving delay.

Tones from number 8 to number 255 can be used:

from 8 to 31 for upsteam signals and from 32 to

255 for downstream signals. Numbers 16 and 64

(96 for ADSL over ISDN) are dedicated to pilot

tones which are employed for synchronisation

purposes with ATU-C end. The software sets the

use of tones for optimisation of performances.

Time recovery is carried out by the chip-set

through the pilot tones. This activity is undertaken

in two steps in order to achieve no more than

2ppm with ATU-C.

The transceiver controller software monitors line

and channel. As far as line is concerned noise

margin, attenuation, power, carrier load, relative

capacity occupation are checked.

Channel’s monitoring deals with cell-delineation,

actual

ATM

(fast

and

interleaved)

up

and

downstream rates.

Figure 1 : ADSL modem block configuration

DMT MODEM ST70135A

UTOPIA

µ CONTROL

MEMORY

AFE

ST70134

χ

χ

UTP