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NT8D09 Analog Message Waiting Line card Page 541 of 894
Circuit Card Description and Installation
Card interfaces
The analog message waiting line card passes voice and signaling data over
DS-30X loops and maintenance data over the card LAN link. These interfaces
are discussed in “Intelligent Peripheral Equipment” on page 30.
Line interface units
The analog message waiting line card contains 16 identical and independently
configurable line interface units (also referred to as circuits). Each unit
provides 600-ohm impedance matching and a balance network in a signal
transformer/analog hybrid circuit. Circuits are also provided in each unit to
apply the ringing voltage onto the line synchronized to the ringing current
zero crossing. Signal detection circuits monitor on-hook/off-hook status and
switchhook flash detection. Four codecs are provided to perform A/D and D/
A conversion of line analog voiceband signals to digital PCM signals. Each
CODEC supports four line interface units. The following features are
common to all units on the card:
• Transmission and reception of Scan and Signaling Device (SSD)
signaling messages over a DS30X signaling channel in A10 format.
• Loopback of SSD messages and pulse code modulation (PCM) signals
for diagnostic purposes.
• Correct initialization of all features, as configured in software, at
power-up.
• Direct reporting of digits dialed (500 telephones) by collecting dial
pulses.
• Connection of –150 V dc at 1 Hz to activate message waiting lamps in
two telephones in parallel. The two telephones must be the same type or
the neon series resistor in each telephone must be 54 K ohms or greater.
• Lamp status detection (will not detect a failure of either lamp when
operating in parallel).
• Disabling and enabling of selected units for maintenance.
• 40 mA to telephones with short circuit protection.