AT&T AT&T manual ATL Line ZTN79, Port Circuits

ATL Line (ZTN79)

The	ATL I,ine Circuit Pack interfaces eight hybrid voice	terminal (7300H series) lines and
the	TDM bus. It terminates three pairs of wires from	each terminal: analog voice pair,

digital control pair, and power pair. Figure 3-11shows the following ATL Line unique circuitry:

● Protocol handler

●Eight port circuit.

Protocol Handler: The 8-bit on-board microprocessor translates the control information in Control Channel Message Set (CCMS) message format to the control information message

format used by	the 7300H series voice terminals.	The protocol handler sends the messages
to the terminals via transceivers located in the port circuits.
Port Circuits:	Each port circuit is identical.	A port circuit consists of an analog port,
one-half of a transceiver, and an electronic power		feed device.

The analog port circuit consists of a codec, a hybrid circuit, an isolation transformer, and associated power filtering circuitry. The codec and hybrid circuit perform the same function as the codec and hybrid circuit in the Analog Line Circuit Pack (TN742). The output of the hybrid circuit is connected to the primary of the isolation transformer. The secondary of the transformer is connected to the analog voice pair.

The transceiver interfaces the voice terminal pair to the protocol handler. The electronic power feed device provides -24 volts de on the power pair to the voice terminal. The device is polled by the on-board microprocessor, periodically and on demand, to test for an overcurrent or no-current condition.

Each Electronic Power Feed (EPF) circuit supports two ports. If one of the associated lines becomes overloaded, the associated pair of lines will also be out of service. One EPF supports Ports O and 1, one Ports 2 and 3, one Ports 4 and 5, and one Ports 6 and 7. The on/off state of the device is controlled by the on-board microprocessor.

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