le79231 Zarlink Semiconductor, le79231 Datasheet - Page 4

• Manufacturer Part Number: le79231
• Description: Intelligent Subscriber Line Interface Circuit
• Manufacturer: Zarlink Semiconductor

The VE790 series ISLAC devices perform 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.
Besides the codec functions, the 790 series chip set provides all the sensing, feedback, and clocking necessary to completely
control the Le79231 ISLIC device functions with programmable parameters. System-level parameters under programmable
control include active loop current limits, feed resistance, and feed mode voltages.
The VE790 series ISLAC devices supply complete mode control to the Le79231 ISLIC device using the control bus (P1-P3) and
tri-level load signal (LD
The 790 series voice chip set 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 measurement data directly
to a higher level processor by way of the PCM voice channel. Both longitudinal and metallic resistance and capacitance can be
measured, which allows leakage resistance, line capacitance, and telephones to be identified.
*Note:
i = channel number
•
•
–
–
A low-level voltage proportional to the voice signal (VOUT
A voltage that controls longitudinal offset for test purposes (VLB
i
).
DC loop current
12 or 16 kHz metering signal
Zarlink Semiconductor Inc.
4
i
)
i
)