ATT System 25 Maintenance Manual

SYSTEM HARDWARE
MET Line (7N735)
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 3-16.
Port Circuits: The four 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...

SYSTEM HARDWARE
Figure 3-16. Unique MET Line (TN735) Circuitry
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SYSTEM HARDWARE
Analog Line (TN742)
The Analog Line circuit pack interfaces eight analog voice terminal lines and
the TDM bus. Figure 3-17 shows the following Analog Line unique circuitry:
l Ringing application circuit
l Port Input/Output (I/O) circuit
l Eight port circuits.
Ringing Application Circuit: This circuit receives ringing voltage from the
power supply. It monitors ringing voltage and current, generates signals to
the on-board microprocessor indicating zero ringing voltage and current, and...

SYSTEM HARDWARE
Note:The TN742 may be used instead of the ZTN78 Tip Ring circuit pack.
The TN742 supports up to five bridged single-line voice terminals;
however, only two may be off-hook at one time. The ZTN78 circuit
pack does not support bridged terminals. In addition, the TN742
supports out-of-building, extended, and off-premises stations; the
ZTN78 does not.
Figure 3-17. Unique Analog Line (TN742) Circuitry
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SYSTEM HARDWARE
DID Trunk (TN753)
The DID Trunk circuit pack interfaces eight central office trunks arranged for
Direct Inward Dialing (DID) and the TDM bus. Figure 3-18 shows the
following DID Trunk unique circuitry:
l Port Input/Output (I/O) circuit
l Eight port circuits.
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...

SYSTEM HARDWARE
Figure 3-18. Unique DID Trunk (TN753) Circuitry
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SYSTEM HARDWARE
Tie Trunk (TN760B)
The Tie Trunk circuit pack 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 is used for signaling. The T and R pair transmits analog signals from the
circuit pack. The T1 and R1 pair receives 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...

SYSTEM HARDWARE
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...

SYSTEM HARDWARE
Table 3-B. TN760B Option Switch Settings and Administration
System 25
Installation
Situation
Circumstance
Co-Located
Inter-Bldg.
Co-Located
Inter-Bldg.
Co-Located
Inter-Bldg.
Co-Located
Inter-Bldg.
Co-Located
To
S25/S75
S25/S75
S85
S85
DIMENSION
PBX
DIMENSION
PBX
Other
Other
Net
Int.
Preferred
Signaling Format
System 25
Simplex
Type 5
Simplex
Type 5
Simplex
Type 5
Simplex
Type 5
E&M
Type 1
Compatible
Prot.
Type 1
Compatible
E&M
Type 1
Compatible
Prot.
Type 1
Compatible
E&M
Type 1...

SYSTEM HARDWARE
Figure 3-20. Tie Trunk (TN760B) Circuit Pack Option Switches
Table 3-C summarizes the conditions present as the transmit and receive
control signals for each signaling type.
Table 3-C. Signaling Type Summary
SIGNALINGTRANSMITRECEIVE
TYPEOn-HookOff-HookOn-HookOff-Hook
I Std.grdbatopen/bat (*)grd
I Compat.
open/bat (*)grdgrd
open/bat (*)
Vopengrd
open
 grd
* An open circuit is preferred over voltage.
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