Instruction manual

FUNCTIONAL DESCRIPTION
Auxiliary Trunk (TN763)
The Auxiliary Trunk Circuit Pack (Figure 3-9) interfaces four ports provided for customer-
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. The Auxiliary
Trunk has the following unique circuitry:
● 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 dc 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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