ATT System 25 Maintenance Manual

							SYSTEM HARDWARE
Physical Characteristics: The TDM bus is an 8-bit bus. The bus snakes
continuously between cabinets in a multicabinet system as shown in Figure
3-8. The total length is about 9 feet for a 3-cabinet system. The bus is
driven from any of the circuit packs in the cabinets. Similarly, a signal on the
bus can be received by any circuit pack.
Within a cabinet, the bus is printed on one side of the circuit pack carrier
backplane, and the other side is solid ground. Ribbon cables are used to
cable the TDM bus between cabinets in a multicabinet system.
Electrical Characteristics: The TDM bus is an unbalanced, low-characteristic
impedance transmission line. Paths printed over a ground plane on the
carriers and the flat ribbon cables between carriers maintain this impedance
level over the full length of the bus.
One end of the bus is terminated to ground with a bus termination circuit card
and the other end is terminated by a network on the ZTN81 (V1) or ZTN127
(V2) Memory CP. Each circuit pack connects to the bus through a custom
bus driver device. The bus driver is a switchable constant current source so
that even in the high output state there is no bus loading to cause
reflections. The current output of the drivers is adjusted so that logic high
is 1.5 volts compared to a low of 0 volts.
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							SYSTEM HARDWARE
TDMBUS
TERMINATOR
CARD
CABINET 3
ON/OFF
SWITCH
AC POWER
# 6 AWG
BUILDING
GROUND
WIRE TDM BUS
EXTENDERCABLE
CABINET 2
AC POWER
#6 AWG
GROUND
WIRE
CABINET
1
COUPLED
BONDING
CONDUCTOR
(CBC)
AC POWER
TO SINGLE
POINT GROUND
Figure 3-8. TDM Bus Diagram—3-Cabinet System
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							SYSTEM HARDWARE
Port Circuits
The following port circuit packs provide the link between trunks and external
equipment and the TDM bus:
l Ground Start Trunk (ZTN76)
l Loop Start Trunk (ZTN77)
l Tip Ring Line (ZTN78).
l ATL Line (ZTN79)
l Data Line (TN726)
l MET Line (TN735)
l Analog Line (TN742)
l DID Trunk (TN753)
l Tie Trunk (TN760B)
l Auxiliary Trunk (TN763)
l STARLAN Interface (ZTN84) (V2)
Figure 3-9 shows the equipment types that can be connected to the digital
switch by the Call Processor and port circuit packs. Figure 3-9 shows only
overall concepts. Some arrangements require auxiliary power and/or
adapters. See the Installation and Test Manual (555-520-100) or Reference
Manual (555-520-200) for complete details.
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							SYSTEM HARDWARE
Figure 3-9.
Equipment Connected to System 25 By Call Processor and
Port Circuit Packs (Sheet 1 of 3)
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							SYSTEM HARDWARE
Figure 3-9.
Equipment Connected to System 25 By the Call Processor
and Port Circuit Packs (Sheet 2 of 3)
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							SYSTEM HARDWARE
LEGEND:ADU –
CAS -
CO -
CP -
DID -
DTU –
FX -
MET –
OPS -
SAT –
SMDR -
WATS -
ASYNCHRONOUS DATA UNIT
CALL ACCOUNTING SYSTEM
CENTRAL OFFICE
CIRCUIT PACK
DIRECT INWARD DIALINGDIGITAL TAPE UNIT
FOREIGN EXCHANGE
MULTIBUTTON ELECTRONIC TELEPHONE
OFF-PREMISES STATION
SYSTEM ADMINISTRATION TERMINAL
STATION MESSAGE DETAIL RECORDING
WIDE AREA TELECOMMUNICATIONS SERVICE
Figure 3-9.Equipment Connected to System 25 By the Call Processor
and Port Circuit Packs (Sheet 3 of 3)
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							SYSTEM HARDWARE
Eight port circuits are provided on most port circuit packs. The MET Line,
Tie Trunk, and Auxiliary Trunk CPs each contain four port circuits. The port
circuits provide an interface between terminals/trunks and the TDM bus. The
STARLAN Interface CP (V2) is unique. It provides one interface (port) to a
Network Extension Unit (NEU) and four connections to the TDM bus.
The number of port circuit packs required varies per customer requirements
and equipment configuration.
Each of the System 25 port circuit packs contain a number of common
elements (see Figure 3-10), such as:
l Bus buffers
l Sanity And Control Interface (SAKI)
l On-board microprocessor with external Random Access Memory (RAM)
l One or more Network Processing Elements (NPEs)
l Circuit Pack Address Leads.
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							SYSTEM HARDWARE
Figure 3-10. Port Circuit Pack Common Circuitry
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							SYSTEM HARDWARE 
						

							SYSTEM HARDWARE
NPEs (Network Processing Element): Each port circuit pack contains one or
two NPEs. The Analog Line, ATL Line, Tip Ring Line, 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 perform 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 systems. The logic values on leads BA4 and BA5
are used to identify the cabinet (Cabinet 1, 2, or 3) and are tied by the cabinet
address plugs to either +5 V dc or ground, as appropriate. Lead BA6 is tied
to ground.
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