AT&T AT&T manual Auxiliary Trunk TN763

Auxiliary Trunk (TN763)

The Auxiliary Trunk Circuit Pack interfaces four ports provided for client-provided equipment (CPE) and the TDM bus. It is connected to the CPE by up to three pairs of wires. The transmission pair (T and R) carry voice signals and touch-tone control signals. The T and R also provide a loop start seizure indication to the CPE. The seizure pair (SZ and SZ1) provide seizure indication to the CPE. The signal pair (S and S1) provide answer supervision and/or make-busy information from the CPE. Depending on the application, either the transmission pair only or all three pairs are connected to the CPE.

Figure 3-18shows the following Auxiliary Trunk unique circuitry:

● Ground detector circuit

●Port Input/Output (I/O) circuit

●Four port circuits.

Ground Detector Circuit: This circuit determines if an answer-supervision or make-busy signal from the CPE is present. The inputs of the ground detector come from the port circuits as an analog current to the -48 volt de supply. Its output is a port control point to the port I/O circuit.

Port I/O Circuit: This circuit consists of bus expanders				for communication	between	the
on-board microprocessor and		the port circuits.	It receives	commands from	the on-board
microprocessor and	distributes	them to the individual port circuits. It also accesses the				port
circuit scan points	and passes the information to		the on-board microprocessor.

Port Circuits: The four port circuits are identical. Each port circuit consists of a codec, hybrid circuit, line transformer, relay driver, battery polarity sensor, and surge protection circuit.

The codec is a 4-wire circuit that converts the analog signal from the CPE to a PCM data signal. It converts an incoming PCM data signal from the NPE to an analog signal. The hybrid circuit converts the 4-wire analog signal from the codec to a 2-wire analog signal that is connected to the CPE by a line transformer.

The relay driver buffers and	inverts	the relay	drive	signals from the port I/O circuit so that
a logic high input operates	the appropriate relay.			The relays	control	circuitry that provide
the proper interfaces for CPE.
The surge protection circuit	provides	lightning	surge	protection	for the	circuit pack.

The circuit pack supports both touch-tone and dial pulse signaling. Longitudinal surges are isolated from the hybrid and codec by the line transformer.

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