Nortel NT1R20, Description

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QPC578 Integrated Services Digital Line Card Page 257 of 290
Line cards Description
Card interfaces
The integrated services digital line card passes voice, data, and signaling over
network loops. This interface is discussed in detail in “Peripheral equipment”
on page 6.
Line interface units
The QPC578 ISDLC is equipped with eight identical line interface units.
Each line interface unit provides a multiplexed voice, data, and signaling path
to and from digital terminal equipment over a 2-wire full duplex 512 kHz time
compression multiplexed (TCM) digital link.
The TCM loop interface circuit provides transformer coupling and foreign
voltage protection between the TCM loop and the digital line interface circuit.
It also provides battery voltage for the digital telephone set.
Multiplex control
The multiplex control logic is common to all four channels. This logic
interfaces the individual line circuits to the peripheral bus signaling channel.
Circuits are provided in the multiplex control logic to retime the digital
signals received from the peripheral bus. Circuits are also provided to decode
the address information contained on the peripheral bus to enable the
individual line circuits during their selected time slots. Further, logic is
provided to enable or disable the front panel LED to indicate the service state
of the card.
Circuit power
A switching power supply on the QPC578 ISDLC card takes either the
–52 V dc or the –48 V dc input and generates the +5 V dc and +10 V dc
required by the ISDLC logic circuits. The ±15.0 V dc inputs to the card are
used to power the loop interface circuits.