ATT System 25 Reference Manual

FUNCTIONAL DESCRIPTION
Figure 3-10.Data Line (TN726) Unique Circuitry
3-20 

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...

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...

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...

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...

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...

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...

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
3-28 

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...