ATT System 25 Reference Manual

FUNCTIONAL DESCRIPTION
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 3-17 shows the Tip and Ring Line
unique circuitry.The TN742 can be used instead of the ZTN78 Tip Ring CP. The TN742
supports up to five bridged single-line voice terminals; however, only two can be off-hook at
one time.The ZTN78 does not support bridged terminals.In addition, the TN742 supports
out-of-building, extended,...

FUNCTIONAL DESCRIPTION
l Port I/O Circuit
This circuit includes 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.
l -48 V To -24 V Power Conditioner
This circuit converts -48 V power from the power supply into a conditioned source of
-24 V power for the electronic battery...

FUNCTIONAL DESCRIPTION
l
lBus Buffers
There are four bus buffers on the circuit pack. The clock driver and receive buffers
interface three system clock signals (2.048 MHz, 8 kHz, and 160 kHz) to the TDM
bus. Two buffers interface the system tones (see Table 3-A) between the TDM bus
and the Service Circuit CP. Music is not provided by the Service Circuit but can be
provided via a port interface on a Tip Ring Line CP (ZTN78).
SAKI
This circuit functions the same as in the SAKI in the common circuitry for...

FUNCTIONAL DESCRIPTION
l 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 (i.e., those tones that vary with time).
l Clock Circuit
The clock circuit consists of a 20.48-MHz oscillator, various dividers, and shift
registers....

FUNCTIONAL DESCRIPTION
lPort I/O and Sanity Check Circuit
This circuit interfaces the on-board microprocessor to the port circuits and checks
the sanity status of the DSPS of the port circuit.
Tone Detector (TN748B)
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 CP consists of the same common circuitry as the intelligent port circuits plus the
unique circuits shown...

FUNCTIONAL DESCRIPTION
l Port Circuits
There are eight port circuits.
Six port circuits are connected to Network Processing
Elements (NPEs). Port circuits 0, 1, 4, and 5 are DTMF tone detector ports. Each of
the six port circuits has an associated Digital Signal Processor (DSP), NPE to DSP
interface circuitry, a DSP restart circuit and an interrupt filter. Port circuits 2 and 6
are general purpose tone detector ports.Port circuits 3 and 7 provide digital loop-
back testing of each NPE on the circuit...

FUNCTIONAL DESCRIPTION
TDM
BUS
LEADS
CIRCUIT
PACKADDRESS
LEADS
Figure 3-20.Pooled Modem (TN758)
l Common Circuitry
The Pooled Modem contains the same common circuitry as port CPs.
l Conversion Resources
The two conversion resources (port circuits) are identical and each contain the
following:
— Microprocessor
— Transmit and Receive I-channel Controller (TRIC)
— Universal Synchronous/Asynchronous Receiver and Transmitter (USART)
— Data USART Clock (DUCK)
— Digital Signal Processor (DSP).
The...

FUNCTIONAL DESCRIPTION
information.It also allows the port circuit microprocessor to inform the on-board
microprocessor of various port circuit status information.
The DUCK and TRIC interface I-channel information between the port circuit and the
remote data module. The microprocessor controls the operation of the DUCK and
the TRIC by programming their internal registers. The DUCK and TRIC together
recreate the clock and serial data stream from the remote data module, and process
an on-board clock and...

FUNCTIONAL DESCRIPTION
Software
The System software consists of switched services,administrative, and maintenance
software. This software runs on top of the real-time operating system software.
Switched Services Software
The switched services software provides voice and data call processing. This software
resides in the Common Control circuitry and in the 8-bit on-board microprocessors located in
the port and service circuits.
The switched services software uses the operating system to provide a process...

FUNCTIONAL DESCRIPTION
Memory Allocation
The system software, like the hardware, is identified by release and version number. Each
version identifies a particular memory configuration for the release number. Main memory is
located in the Common Control circuitry, that is, the CPU/MEM Circuit Pack.
Real-Time Constraints
Real-time constraints are a function of the speed of the common control circuitry and the
traffic load. The switch is designed so that many time-consuming and repetitious functions
are...