ATT System 25 Maintenance Manual

SYSTEM HARDWARE
Ground Start Trunk (ZTN76)
The Ground Start Trunk circuit pack interfaces eight central office trunks and
the TDM bus. Figure 3-11 shows the following Ground Start Trunk unique
circuitry:
l Ground detector circuit
l Port Input/Output (I/O) circuit
l Eight port circuits.
Ground Detector Circuit: The ground detector circuit determines if ground
has been applied to the tip lead for incoming seizure. It also senses tip
ground on outgoing seizure indicating dial tone is present. One ground...

SYSTEM HARDWARE
Figure 3-11. Unique Ground Start Trunk (ZTN76) Circuitry
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SYSTEM HARDWARE
Loop Start Trunk (ZTN77)
The Loop Start Trunk circuit pack interfaces eight central office loop start
trunks and the TDM bus. Figure 3-12 shows the following Loop Start Trunk
unique circuitry:
l Port Input/Output (I/O) circuit
l 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....

SYSTEM HARDWARE
Figure 3-12. Unique Loop Start Trunk (ZTN77) Circuitry
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SYSTEM HARDWARE
Tip Ring Line (ZTN78)
The Tip Ring Line circuit pack interfaces eight analog tip and ring voice
terminal lines (single-line voice terminals) and the TDM bus. Figure 3-13
shows the following Tip and Ring Line unique circuitry:
l Ringing application circuit
l Port Input/Output (I/O) circuit
l –48 V to -24 V Power Conditioner
l Eight port circuits.
Ringing Application Circuit: This circuit receives ringing voltage from the
power supply. It monitors ringing voltage and current and generates...

SYSTEM HARDWARE
Figure 3-13. Unique Tip Ring Line (ZTN78) Circuitry
3-34 

SYSTEM HARDWARE
ATL Line (ZTN79)
The ATL Line circuit pack interfaces eight hybrid voice terminal (7300H
series) lines and the TDM bus. It terminates three pairs of wires from each
terminal: analog voice pair, digital control pair, and power pair. Figure 3-14
shows the following ATL Line unique circuitry:
l Protocol handler
l Eight port circuits.
Protocol Handler: The 8-bit on-board microprocessor translates the control
information in CCMS message format to the control information message
format used by...

SYSTEM HARDWARE
Figure 3-14. Unique ATL Line (ZTN79) Circuitry
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SYSTEM HARDWARE
Data Line (TN726)
The Data Line circuit pack interfaces eight Asynchronous Data Units (ADUs)
data devices and the TDM bus. The ADUs are typically, in turn, connected to
RS-232C-type devices. Figure 3-15 shows the Data Line unique circuitry that
includes:
l A bit clock
l Bus isolation
l Eight port circuits.
Bit Clock: The bit clock circuitry is used to provide the OATMEALs (Octal
Asynchronous Terminal Mode Two EIA Asynchronous LSIs) with a clock
frequency that is a multiple of each baud...

SYSTEM HARDWARE
Figure 3-15. Unique Data Line (TN726) Circuitry
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