am79r251 Advanced Micro Devices, am79r251 Datasheet - Page 9

• Manufacturer Part Number: am79r251
• Description: Intelligent Subscriber Line Interface Circuit Islic
• Manufacturer: Advanced Micro Devices

GENERAL DESCRIPTION
The Intelligent Access voice chipsets integrate all functions of the subscriber line. Two chip types
are used to implement the linecard; an Am79R251 device and an ISLAC device. These provide the
following basic functions:
1. The Am79R251: A high voltage, bipolar device that drives the subscriber line, maintains
2. The ISLAC device: A low voltage CMOS IC that provides conversion, control and DSP functions
Complete schematics of linecards using the Intelligent Access voice chipsets for internal and external
ringing are shown in Figure 3 and Figure 4.
The Am79R251 uses reliable, bipolar technology to provide the power necessary to drive a wide
variety of subscriber lines. It can be programmed by the ISLAC device to operate in eight different
modes that control power consumption and signaling. This enables it to have full control over the
subscriber loop. The Am79R251 is designed to be used exclusively with the ISLAC devices. The
Am79R251 requires only +5 V power and the battery supplies for its operation.
The Am79R251 implements a linear loop-current feeding method with the enhancement of intelligent
Thermal Management. This limits the amount of power dissipated on the Am79R251 chip by
dissipating power in external resistors in a controlled manner.
Each ISLAC device contains high-performance circuits that provide A/D and D/A conversion for the
voice (codec), DC-feed and supervision signals. The ISLAC device contains a DSP core that handles
signaling, DC-feed, supervision and line diagnostics for all channels.
The DSP core selectively interfaces with three types of backplanes:
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The Intelligent Access voice chipset provides a complete software configurable solution to the
BORSCHT functions as well as complete programmable control over subscriber line DC-feed
characteristics, such as current limit and feed resistance. In addition, these chipsets provide system
level solutions for the loop supervisory functions and metering. In total, they provide a programmable
solution that can satisfy worldwide linecard requirements by software configuration.
Software programmed filter coefficients, DC-feed data and supervision data are easily calculated
with the WinSLAC
to enter a description of system requirements. WinSLAC then computes the necessary coefficients
and plots the predicted system results.
The Am79R251 interface unit inside the ISLAC device processes information regarding the line
voltages, loop currents and battery voltage levels. These inputs allow the ISLAC device to place
several key Am79R251 performance parameters under software control.
The main functions that can be observed and/or controlled through the ISLAC backplane interface
are:
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Standard PCM/MPI
Standard GCI
Modified GCI with a single analog line per GCI channel
DC-feed characteristics
Ground-key detection
Off-hook detection
Metering signal
Longitudinal operating point
Subscriber line voltage and currents
Ring-trip detection
Abrupt and smooth battery reversal
longitudinal balance and senses line conditions.
for the Am79R251.
software. This PC software is provided free of charge. It allows the designer
Am79R251
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