10
Am79231 Data Sheet
Ringing
Sophisticated line and circuit tests
To accomplish these functions, the ISLIC device collects the following information and feeds it, in
analog form, to the ISLAC device:
The metallic (IMT) and longitudinal (ILG) loop currents
The AC (VTX) and DC (VSAB) loop voltage
The outputs supplied by the ISLAC device to the ISLIC device are then:
A voltage (VHLi) that provides control for the following high-level ISLIC device outputs:
—DC loop current
—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)
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 attenua-
tion 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.
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 resis-
tance, 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, 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 measurement data directly to a higher level processor by way
of the PCM voice channel. Both longitudinal and metallic resistance and capacitance can be mea-
sured, which allows leakage resistance, line capacitance, and telephones to be identified.
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