Instruction manual

FUNCTIONAL DESCRIPTION
● NPE (Network Processing Element)
Each port circuit pack contains one or two NPEs. The Analog Line, ATL Line, Tip
Ring, Data Line, Ground Start, Loop Start, and DID Trunk Circuit Packs contain two
NPEs. The MET Line, Auxiliary Trunk, and Tie Trunk Circuit Packs contain one NPE.
The NPEs do switching network functions for the port circuits. Under control of the
on-board microprocessor, an NPE can connect a port circuit to any one of the TDM
bus time slots. More specifically, it allows a port circuit to talk on one time slot and
listen to the same time slot (NPE sidetone) and on up to four other time slots at the
same time. In 2-wire circuits that provide their own sidetone, the NPE sidetone is not
used.
● Circuit Pack Address Leads
Seven leads (BA0-BA6) are tied to corresponding logic levels to uniquely identify
each CP slot in the system, including multiple cabinet system. The logic values on
leads BA4 and BA5 are used to identify the cabinet (Cabinet 1, 2, or 3) and are tied
via the cabinet address plugs to either +5 V dc or ground, as appropriate. Lead BA6
is tied to ground.
Analog Line (TN742)
The Analog Line CP (Figure 3-7) interfaces eight analog voice terminal lines and the TDM
bus. The TN742 can be used instead of the ZTN78 Tip Ring CP. The TN742 supports up to
five bridged single-line voice terminals, but only two can be off hook at one time. The ZTN78
CP does not support bridged terminals.
In addition, the TN742 supports out-of-building,
extended, and off-premises stations, the ZTN78 does not. The Analog Line has the following
unique circuitry:
● Ringing Application Circuit
This circuit receives ringing voltage from the power supply. It monitors ringing
voltage and current, generates signals to the on-board microprocessor indicating
zero ringing voltage and current, and detects a terminal user lifting the receiver
during ringing.
This prevents the application of ringing to the port circuit when a
terminal user lifts the receiver during the ringing phase.
Maintenance circuitry is also
included. The maintenance circuitry detects when a terminal is connected to the port
circuitry and checks for faults in the ringing application circuitry.
● Port I/O Circuit
This circuit consists of bus expanders connecting 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.
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