Nortel NT1R20, Description

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NT8D09 Analog Message Waiting Line Card Page 219 of 290
Line cards Description
Signaling and control
The signaling and control portion of the card provides circuits that establish,
supervise, and take down call connections. These circuits work with the
system CPU to operate the line interface circuits during calls. The circuits
receive outgoing call signaling messages from the CPU and return incoming
call status information over the DS-30X network loop.
Circuit power
The +8.5 V dc input is regulated down to +5 V dc for use by the digital logic
circuits. All other power to the card is used by the line interface circuits. The
+15.0 V dc input is regulated down to +12 V dc to power the analog circuits.
The –48.0 V dc input is for telephone set battery.
Ringing power for telephone sets is 86 Vrms ac at 20 Hz on –48 V dc. The
Rsync signal is used to switch 20 Hz ringing on and off at the zero current
cross-over point to lengthen the life of the switching circuits.
Power for lighting the message waiting lights is provided by either the
peripheral equipment power supply or the ringing generator. Logic on the
message waiting line card interrupts the –150 V dc signal at 1 Hz intervals to
provide a flashing message waiting light.