ATT System 25 Maintenance Manual

SYSTEM HARDWARE
Auxiliary Trunk (TN763)
The Auxiliary Trunk circuit pack interfaces four ports provided for customer-
provided equipment (CPE) and the TDM bus. It is connected to the CPE by
up to three pairs of wires. The transmission pair (T and R) carries voice
signals and touch-tone control signals. T and R also provides a loop start
seizure indication to the CPE. The seizure pair (SZ and SZ1) provides
seizure indication to the CPE. The signal pair (S and S1) provides answer
supervision and/or...

SYSTEM HARDWARE
The surge protection circuit provides lightning surge protection for the circuit
pack. Longitudinal surges are isolated from the hybrid and codec by the line
transformer.
Figure 3-21. Unique Auxiliary Trunk (TN763) Circuitry
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SYSTEM HARDWARE
System Resources
The System Resource circuit packs are as follows:
l Service Circuit (ZTN85)
l Tone Detector (TN748)
l Pooled Modem (TN758).
Service Circuit (ZTN85)
The Service Circuit circuit pack provides the systems clock signals. It also
generates and receives tones. The Service Circuit circuit pack (Figure 3-22)
consists of the following:
l Bus buffers
l Sanity And Control Interface (SAKI)
l On-board microprocessor with external RAM
l Clock circuit
l Tone Generator
l Time slot table...

SYSTEM HARDWARE
On-Board Microprocessor With External RAM: This circuit functions the
same as the microprocessor in the common circuitry for the intelligent port
circuits. In addition, it tells the dual-port RAM in the time slot table circuit the
appropriate time slots in which to place a tone. The external RAM also has
work space for complex tones (that is, those tones that vary with time).
Clock Circuit: The clock circuit consists of a 20.48-MHz oscillator, various
dividers, and shift registers. The...

SYSTEM HARDWARE
Port I/O and Sanity Check Circuit: This circuit interfaces the on-board
microprocessor to the port circuits and checks the sanity status of the port
circuits DSPs.
Figure 3-22. Service Circuit (ZTN85)
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SYSTEM HARDWARE
Tone Detector (TN748)
The Tone Detector circuit pack provides four touch-tone receivers and two
general purpose tone receivers that detect appropriate system and network
tones on the TDM bus.
The Tone Detector circuit pack consists of the same common circuitry as the
intelligent port circuits and the following unique circuits (see Figure 3-23):
l Port I/O circuit
l Port and DSP Sanity check circuit
l Four touch-tone port circuits
l Two general purpose tone detector port circuits
l Two NPE...

SYSTEM HARDWARE
Figure 3-23. Tone Detector (TN748) Circuit
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SYSTEM HARDWARE
Pooled Modem (TN758)
The Pooled Modem circuit pack supports 0-300 and 1200 bits per second
(bps) data speeds and provides the following:
l
l
lCircuitry to provide a signal compatible with the modulation formats of
the 212-series modems
Modem emulation (see below)
CapabilityData Module Mode
0-300 AsynchronousLow
300 Asynchronous300 Asynchronous
1200 Asynchronous1200 Asynchronous
Modem control functions corresponding to 212-series modem operations.
A maximum of two Pooled Modem circuit...

SYSTEM HARDWARE
Figure 3-24. Pooled Modem (TN758) Circuit
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SYSTEM HARDWARE
Common Circuitry: The Pooled Modem common circuitry, which includes all
circuitry shown on Figure 3-24 except the Conversion Resource circuitry,
provides the same general function as the intelligent port common circuitry.
Conversion Resources: The two conversion resources (port circuits) are
identical and each contains the following:
l Microprocessor
l Transmit and Receive l-channel Controller (TRIC)
l Universal Synchronous/Asynchronous Receiver and Transmitter (USART)
l Data USART Clock...