ATT System 25 Reference Manual

							FUNCTIONAL DESCRIPTION
Figure 3-10.Data Line (TN726) Unique Circuitry
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							FUNCTIONAL DESCRIPTION
l Port Circuits
Each of the eight identical port circuits allows the connection of interface equipment
having an RS-232 compatible serial interface to the switch. The circuit provides
asynchronous full duplex data transport at standard speeds from 300 to 19,200 bps
and a low data rate (
						

							FUNCTIONAL DESCRIPTION
NPE 0
NPE 1
ON-BOARD
MICROPROCESSOR
Figure 3-11.DID Trunk (TN753) Unique Circuitry
Ground Start Trunk (ZTN76j
TOCENTRAL
OFFICE
The Ground Start Trunk CP (Figure 3-12) interfaces eight central office trunks and the TDM
bus. The Ground Start Trunk has the following unique circuitry:
l 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 sensor is used for each port circuit. Input for the ground
sensor comes from the port circuit as an analog current to the -48 volt dc supply.
The output of the ground sensor is a port control point to the port I/O circuit.
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							FUNCTIONAL DESCRIPTION
NPE 0
NPE 1
ON-BOARD
MICROPROCESSOR
TO
CENTRAL
OFFICE
Figure 3-12.
Ground Start Trunk (ZTN76) Unique Circuitry
l 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. It also accesses
the port circuit scan points and passes the information to the on-board
microprocessor.
l Port Circuits
The eight port circuits are identical.
Each port circuit consists of a coder/decoder
(codec), hybrid circuit, line transformer, relay driver, and surge protection circuit.
The codec is a 4-wire circuit that converts the NPEs digital output to an analog
signal. Likewise, it converts the analog signal from a central office trunk to a Pulse
Code Modulated (PCM) data signal to the NPE. The hybrid circuit converts the codec
4-wire analog signal to a 2-wire analog signal that is connected to the central office
trunk by the line transformer.
The relay driver buffers and inverts the relay drive signals from the port I/O circuit so
that a logic high input operates the appropriate relay. The relays control circuitry
provides the proper signaling for ground start trunks. The trunks support touch-tone
dialing. The surge protection circuit provides overvoltage lightning surge protection.
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							FUNCTIONAL DESCRIPTION
Loop Start Trunk (ZTN77)
The Loop Start Trunk Circuit Pack interfaces eight central office loop start trunks and the
TDM bus. Figure 3-13 shows the Loop Start Trunk unique circuitry.
NPE 0
NPE 1
ON-BOARD
MICROPROCESSOR
Figure 3-13.Loop Start Trunk (ZTN77) Unique Circuitry
l Port I/O Circuit
TOCENTRAL
OFFICE
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. It also accesses
the port circuit scan points and passes the information to the on-board
microprocessor.
l Port Circuits
The eight port circuits are identical. Each port circuit consists of a codec, hybrid
circuit, line transformer, relay driver, and surge protection circuit. The codec is a 4-
wire circuit that converts the NPEs output to an analog signal. Likewise, it converts
the analog signal from a central office trunk to a PCM data signal to the NPE. The
hybrid circuit converts the codec 4-wire analog signal to a 2-wire analog signal that is
connected to the central office trunk by the line transformer. The relay driver buffers
and inverts the relay drive signals from the port I/O circuit so that a logic high input
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							FUNCTIONAL DESCRIPTION
operates the appropriate relay.The relays control circuitry provides the proper
signaling for loop start trunks. The trunks support touch-tone dialing and dial pulse
signaling.The surge protectioncircuit provides overvoltage lightning surge
protection for the circuit pack.
MET Line (TN735)
The MET Line Circuit Pack interfaces four Multibutton Electronic Telephone (MET) lines and
the TDM bus. The MET Line unique circuitry consists of four port circuits as shown in Figure
3-14.
NPE
ON-BOARD
MICRO-
PROCESSORTO MET
TERMINALS
MET Line (TN735) Unique Circuitry
Figure 3-14.
Circuits
l Port
Thefour port circuits are identical.Each port circuit consists of an analog port, a
digital port, and an electronic power feed device.The analog port circuit consists of
a codec, a hybrid circuit, an electronic battery feed, and a power filter. The codec,
hybrid circuit, and power filter perform the same function as in the Analog Line
Circuit Pack (TN742). The electronic battery feed provides talking battery to the MET
set, produces a controlled dc battery feed current for short and long loops, and
detects when a MET set user lifts a receiver. The digital port circuit provides a full
duplex channel over two 2-wire pairs. All outgoing lamp
button depression (BT, BR) information is carried on these(LT, LR) and incoming
channels. Ringing and
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							FUNCTIONAL DESCRIPTION
switchhook information is also sent over these channels.
The electronic power feed device provides phantomed -48 volt dc power for the MET
terminals over the data channels.The electronic power feed device is a “smart”
circuit breaker. When it senses an overcurrent condition, it indicates the condition on
an output lead and goes into thermal shutdown if not turned off by the on-board
microprocessor.When the overcurrent condition disappears, the circuit breaker can
be turned on by the on-board microprocessor.
STARLAN Interface (ZTN84)
The STARLAN Interface (ZTN84) Circuit Pack functions as either a gateway or a bridge
between System 25 and the AT&T STARLAN NETWORK (Release 2 of STARLAN only). The
ZTN84 CP contains much of the circuitry common to the other CPS in the system, that is a
Sanity and Control Interface (SAKI), a Network Processing Element (NPE), and a 8031
microprocessor.The CP also contains the circuitry required to perform the protocol
conversion on the data as it travels from one system to the other. These devices include a
80186 microprocessor, 82586 coprocessor, four Octal Asynchronous Terminal Mode 2 to EIA
Asynchronous LSI (OATMEAL) devices, and a logic sequencer. The 80186, the 82586, and
the logic sequencer (PLS105N) work together to add and delete the protocol used by the
Local Area Network (LAN), while the 80186 and the OATMEALS work together to add and
delete the protocol used by the PBX.
The ZTN84 can support up to four circuit switch connections between the Private Branch
Exchange (PBX) and the Local Area Network (LAN); this capability is provided by the four
OATMEALS and the NPE, the latter being a four channel device. In providing a connection
between the PBX and the LAN, capabilities such as file sharing, printer services, connections
to hosts, and modem pooling may be accessible across systems.
The OATMEAL devices on the ZTN84 are used in such a way as to support asynchronous
data communication at any of the standard rates ranging from 300 bps to 19.2 Kbps. The
asynchronous protocol that is used is a subset of Digital Communications Protocol (DCP)
Mode 2, as only “I” channel information is transmitted, where the data is formatted in High-
Level Data Link Control (HDLC) frames.
The ZTN84 has been designed with a hardware interface that allows the CP to be connected
to a STARLAN NETWORK as an OUT connection.This can be connected to a STARLAN
NETWORK Extension Unit (NEU) IN connection, in a star configuration.
The design of the ZTN84 is not fully compatible with the daisy-chain arrangement of the
STARLAN NETWORK, since much of the daisy-chain circuitry was left off of the card. For
testing purposes, the card can be used in a limited daisy-chain arrangement, where the
ZTN84 is connected to a personal computer (PC) that possesses a Network Access Unit
(NAU). The ZTN84 and the PC should be the only two devices forming the LAN. The daisy-
chain circuitry was omitted in order to reduce cost and save board space. It is also the
architectural design of the system that the PBX be connected to the LAN by a NEU. The NEU
can either be local, in the telephone room with the switch, or in a remote office.
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							FUNCTIONAL DESCRIPTION
Tie Trunk (TN760B)
The Tie Trunk Circuit Pack (Figure 3-15) interfaces four 6-wire tie trunks and the TDM bus.
Two tip and ring pairs form a 4-wire analog transmission line. An E and M pair are used for
signaling. The T and R pair transmit analog signals from the circuit pack. The T1 and R1 pair
receive analog signals from the tie trunk. The E and M pair are dc signaling leads used for
call setup handshaking. The E lead receives signals from the tie trunk and the M lead
provides signals from the circuit pack. The TN760Bs four port circuits support Type I, Type I
Compatible, or Type V signaling. Incoming and outgoing trunks can be either automatic,
immediate start, wink start, or delay dial. The Tie Trunk has the following unique circuitry:
l Ground Detector Circuit
This circuit determines if a ground has been applied to the E lead. Ground detector
inputs come from the port circuits as an analog current to the -48 volt dc supply. Its
output is a port control point to the port I/O circuit.
l 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. It also accesses
the port circuit scan points and passes the information to the microprocessor.
l Port Circuits
The four port circuits are identical, except for port 3 where part of the E-lead
maintenance circuit is located. Each port circuit consists of a codec with associated
input and output line transformers, analog operational amplifiers, a power filter.
loop-around transistors, port control comparators, a relay driver, an electronic power
feed device, an E-lead test maintenance circuit, and surge protection circuits.
The codec converts the incoming 4-wire analog signal from the tie trunk to a PCM
data signal. The codec converts the incoming PCM data signal from the NPE to an
analog signal. outgoing and incoming line transformers provide dc isolation to the tip
and ring leads.Analog operational amplifiers provide amplification and buffering for
the codec and network and loop-around gain compensation. Filtered power is
provided to the codec and amplifiers.
The loop-around transistors are under control of the port control comparators and
provide a loop-around path for the signal for testing purposes. The relay driver
buffers and inverts the relay drive signals from the port I/O circuit so that a logic high
input operates the appropriate relay.The relays and electronic power feed device
control the M-lead circuitry to provide the proper signaling handshake for call
progress tones and dial pulse dialing.
The electronic feed device provides a -48 volt dc current to the M-lead circuits. It
also tests the M-lead circuits for opens or shorts and prevents uncontrolled operation
during power-up.The E-lead test circuit provides a ground to the ground detector
circuit for testing purposes.The surge protection circuitry provides lightnlng surge
and power cross protection for the circuit pack.For each port circuit, E&M/Simplex
and surge protection are selected by switch settings as shown on Figure 3-16.
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							FUNCTIONAL DESCRIPTION
The signaling type is administrable for each port. Table 3-B summarizes the
conditions present as the transmit and receive control signals for each signaling type.
Table 3-C lists the preferred TN760B tie trunk signaling format to be used in the
likely-to-be-encountered installation situations.
Figure 3-15.Tie Trunk (TN760B) Unique Circuitry
UNPROT.
PORT: 4 3 2 1
PROT.
Figure 3-16.Tie Trunk (TN760B) Circuit Pack Option Switches
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							FUNCTIONAL DESCRIPTION
Table 3-B.Signaling Type Summary
SignalingTransmit
Receive
Type
On-HookOff-HookOn-HookOff-Hook
I Std.
grd
bat
open/bat (*)
grd
I Compat.
open/bat (*)
grd
grd
open/bat (*)
Vopengrd
opengrd
* An open circuit is preferred over voltage.
Table 3-C. TN760B Tie Trunk Preferred Signaling Formats
Installation Situation
Preferred Signaling Format
System 25
Far End
Simplex
Protected
FromCircum-Simplex
Protected
StancesTo
orSignaloror
SignalorE&MType
Unprotected
(Note 1)E&MType(Note 2)
(Note 1)Unprotected
S25Co-S25/S75SimplexType V(Either)SimplexType VLocated(Either)DEFINITY
S25Inter-S25/S75SimplexType VBuildingDEFINITY(Either)SimplexType V(Either)
S85S25Co-DEFINITYSimplexType V(Either)SimplexType V(Either)
Located
S25Inter-S85
BuildingDEFINITYSimplexType V(Either)SimplexType V(Either)
Type IS25Co-Dim.E&MUnprotectedE&MType IUnprotectedLocatedCompatibleStandard
S25Inter-
Dim.E&MType I
ProtectedE&MType I
BuildingCompatible
StandardProtected
S25Co-OtherE&MType I
UnprotectedE&MType I
UnprotectedLocatedCompatible
Standard
S25Inter-OtherE&MType I
Type I
BuildingCompatibleProtectedE&MStandard(Note 3)
S25NetworkE&MType I
Unprotected(Don’t(Don’t(Don’t
Interface
Standard
Care)
Care)
Care)
Notes:  1. Set by switches on Tie Trunk CP (Figure 3-16).
2. Set by System Administration of Port Options (Action 37).
3. Requires a protection unit.
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