am79d2251 Advanced Micro Devices, am79d2251 Datasheet - Page 10

• Manufacturer Part Number: am79d2251
• Description: Dual Intelligent Subscriber Line Audio-processing Circuit Islac
• Manufacturer: Advanced Micro Devices

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The main functions that can be observed and/or controlled through the ISLAC backplane interface are:
To accomplish these functions, the ISLIC device collects the following information and feeds it, in
analog form, to the ISLAC device:
The outputs supplied by the ISLAC device to the ISLIC device are then:
The ISLAC device performs the codec and filter functions associated with the four-wire section of
the subscriber 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
function, permit adjustment of the two-wire termination impedance and provide frequency
attenuation adjustment (equalization) of the receive and transmit paths. Adaptive transhybrid
balancing is also included. All programmable digital filter coefficients can be calculated using
WinSLAC software. The PCM codes can be either 16-bit linear two’s-complement or 8-bit
companded A-law or µ-law, with the further option of 32 or 24 kb/s ADPCM compression.
Besides the codec functions, the Intelligent Access voice chipset provides all the sensing, feedback,
and clocking necessary to completely control ISLIC device functions with programmable parameters.
System-level parameters under programmable control include active loop current limits, feed
resistance, and feed mode voltages.
The ISLAC device supplies complete mode control to the ISLIC device using the control bus (P1-P3)
and tri-level load signal (LDi).
The Intelligent Access voice chipset provides extensive loop supervision capability including off-hook,
DTMF, ring-trip and ground-key detection. Detection thresholds for these functions are programmable.
A programmable debounce timer is available that eliminates false detection due to contact bounce.
For subscriber line diagnostics, AC and DC line conditions can be monitored using built in test tools.
Measured parameters can be compared to programmed threshold levels to set a pass/fail bit. The
user can choose to send the actual PCM measurement data directly to a higher level processor by
way of the voice channel. Both longitudinal and metallic resistance and capacitance can be
measured, which allows leakage resistance, line capacitance, and telephones to be identified.
DC-feed characteristics
Ground-key detection
Off-hook detection
DTMF detection
Modem tone (2100 Hz) detection
Metering signal
Longitudinal operating point
Subscriber line voltage and currents
Ring-trip detection
Abrupt and smooth battery reversal
Subscriber line matching
Ringing generation
Sophisticated line and circuit tests
The metallic (IMT) and longitudinal (ILG) loop currents
The AC (VTX) and DC (VSAB) loop voltage
A voltage (VHLi) that provides control for the following high-level ISLIC device outputs:
—DC loop current
—Internal ringing signal
—12 or 16 kHz metering signal
A low-level voltage proportional to the voice signal (VOUTi)
A voltage that controls longitudinal offset for test purposes (VLBi)
Am79D2251