AM79C202 Legerity, AM79C202 Datasheet - Page 10

• Manufacturer Part Number: AM79C202
• Description: (AM79C202 / AM79212) PCM CODEC
• Manufacturer: Legerity

ASLIC/ASLAC DEVICES FUNCTIONAL DESCRIPTION
The ASLIC/ASLAC devices chip set integrates all func-
tions of the subscriber line. The chip set comprises an
ASLIC device and an ASLAC device. The set provides
two basic functions: 1) the ASLIC device, a high-voltage,
bipolar device that drives the subscriber line, maintains
longitudinal balance, and senses line conditions, and
2) the ASLAC device, a low-voltage, CMOS device that
combines CODEC, DC Feed control, and line supervi-
sion. A complete schematic of a linecard using the
ASLIC/ASLAC devices chip set is shown in Figure 7.
The ASLIC device uses reliable, bipolar technology to
provide the power necessary to drive a wide variety of
subscriber lines. It can be programmed by the ASLAC
device to operate in eight different states that control
Power Consumption and Signaling modes. This en-
ables full control over the subscriber loop. The ASLIC
device is customized to be used exclusively with the
ASLAC device providing a two-chip universal line inter-
face. The ASLIC device requires only a +5 V power
supply and a negative battery supply for its operation.
The ASLIC device implements a linear loop current
feeding method with the enhancement of thermal man-
agement to limit the amount of power dissipated on the
ASLIC device by dissipating excess power in an external
resistor.
The ASLAC device is a high-performance, CMOS
CODEC/filter device with additional digital filters and
circuits that allow software control of transmission,
DC Feed, and supervision.
Advanced CMOS technology makes the ASLAC device
an economical device that has both the functionality and
the low power consumption required by linecard design-
ers to maximize linecard density at minimum cost.
When used with an ASLIC device, the ASLAC device
provides a complete software-configurable solution to
linecard functions as well as complete programmable
control over subscriber line DC Feed characteristics. In
addition, the ASLIC/ASLAC devices chip set provides
system-level solutions for the loop supervisory functions
and metering. In total, the ASLIC/ASLAC devices chip set
provides a programmable solution that can satisfy world-
wide linecard requirements by software configuration.
All software-programmed coefficients and DC Feed pa-
rameters are easily calculated with the AmSLAC3
ware. This software is provided free of charge and runs
on an IBM-compatible PC. It allows the designer to enter
a description of system requirements, then the software
returns the necessary coefficients and the predicted
system response.
The ASLAC device uses the General Control Interface
(GCI) protocol to interface with the back plane highway.
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Am79212/Am79C202 Data Sheet
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The ASLIC device interface unit inside the ASLAC device
processes information regarding line voltages, loop cur-
rents, and battery voltage levels. These inputs allow the
ASLAC device to place several key ASLIC device perfor-
mance parameters under programmable supervision.
The main functions that can be observed and/or controlled
through the ASLAC device control interface are:
















To accomplish these functions, the ASLAC device col-
lects the following information from the ASLIC device
and the Central Office system:




The outputs supplied by the ASLAC device are then:






The ASLAC device performs the CODEC and filter func-
tions associated with the four-wire section of the sub-
scriber line circuitry in a digital switch. These functions
involve converting an analog voice signal into digital
PCM samples and converting digital PCM samples back
into an analog signal. During conversion, digital filters
are used to band-limit the voice signals.
The user-programmable filters set the receive and
transmit gain, perform the transhybrid balancing func-
tion, permit adjustment of the two-wire termination im-
pedance,
adjustment (equalization) of the receive and transmit
paths. Adaptive transhybrid balancing is also included.
DC Feed characteristics
Ground-key detection
Off-hook detection
Metering signal
Longitudinal operating point
Subscriber line voltage and currents
Ring trip
Abrupt and smooth battery polarity reversal
The sum and difference of the currents in each loop
leg, ISUM, and IDIF
Currents proportional to:
— The voltage across the loop (IAB)
— The battery voltage (IBAT)
— The ringing current in the loop (IRTA - IRTB)
A current proportional to the desired DC loop cur-
rent (IDC)
A voltage proportional to the desired longitudinal off-
set voltage (VLBIAS)
A 12/16 kHz metering signal (appears on VM for
12/16 kHz teletax)
and
provide
frequency
attenuation