Instruction manual

FUNCTIONAL DESCRIPTION
Figure 3-7. Analog Line (TN742) Unique Circuitry
● Port Circuits
The eight port circuits are identical. Each port circuit consists of a coder/decoder (codec),
hybrid circuit, electronic battery feed circuit, ring relay, and overvoltage surge protection
circuit.
The codec is a 4-wire circuit that converts the analog signal from a voice terminal to a PCM
data signal. It converts an incoming PCM data signal from the NPEs 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 analog line. Filtered power is provided for the codec and
hybrid circuits.
November 1995 3-15