ST70134 - ST70135A
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.
Figure 1 : ADSL modem block configuration
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
DMT MODEM ST70135A