Instruction manual

FUNCTIONAL DESCRIPTION
The electronic battery feed circuit provides talking battery to the voice terminal. It also
produces a controlled dc battery feed for short and long loops, detects when a receiver is
lifted, and provides the message waiting signal by periodically turning off the feed voltage.
The ring relay provides the interface between the ringing application circuit and the port
circuit. It causes ringing turn on and turn off.
The overvoltage surge protection circuit provides lightning surge and power line cross-
protection for the circuit pack.
ATL Line (ZTN79)
The ATL Line CP (Figure 3-8) interfaces eight ATL voice terminals corded and/or cordless (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. The ATL Line has the following unique circuitry:
● 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 -48 volts dc 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 0 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.
3-16
November 1995