Instruction manual

FUNCTIONAL DESCRIPTION
NPE 0
NPE 1
ON-BOARD
MICROPROCESSOR
TO
CENTRAL
OFFICE
Figure 3-12.
Ground Start Trunk (ZTN76) Unique Circuitry
● 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 coder/decoder
(codec), hybrid circuit, line transformer, relay driver, and surge protection circuit.
The codec is a 4-wire circuit that converts the NPEs digital output to an analog
signal. Likewise, it converts the analog signal from a central office trunk to a Pulse
Code Modulated (PCM) data signal to the NPE. The hybrid circuit converts the codec
4-wire analog signal to a 2-wire analog signal that is connected to the central office
trunk by the 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
provides the proper signaling for ground start trunks. The trunks support touch-tone
dialing. The surge protection circuit provides overvoltage lightning surge protection.
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