Filter
Top Products
DID Trunk (TN753)
The DID Trunk Circuit Pack interfaces eight central office trunks arranged for Direct
Inwrd Dialing ((DID) and the TDM bus.
Figure 3-15 shows the following DID Trunk unique
circuitry:
● Port Input/output (1/0) circuit
● Eight port circuits.
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 eight port circuits are identical.
Each port circuit consists of a codec,
balance network, trunk interface unit, and loop termination circuit.
The codec is a 4-wire circuit that converts the NPEs output to an analog signal. Likewise, it
converts the analog signal from the Central Office (CO) to a PCM signal to the NPE.
The trunk interface unit contains a hybrid, a 2-wire interface circuit, and control circuitry.
The hybrid circuit converts the 4-wire analog signal from the codec to a 2-wire analog signal
that is connected to the analog line by the 2-wire interface circuit. The control circuitry
controls loop current, internal signal gain, terminating resistance, battery feed shutdown,
and battery reversal. The circuit pack accepts both dial pulse and touch-tone signaling.
The loop termination circuit provides a fixed impedance to the DID trunk.
3-30