Instruction manual

Hardware Overview
025-9416 25
End-to-End Trunk Configuration
The end-to-end trunk configuration is illustrated in Section 11 (Part No. 024-0077). Battery
voltage is provided by the telco equipment; typically TIP (+), RING (-). A bi-directional opto-
isolator monitors the TIP/RING pair to detect inbound ringing from the telco or PABX equip-
ment. After ring detection, the loop relay closure completes the TIP/RING circuit loop to answer
inbound ringing. After the telco equipment detects loop current, ringing is halted and audio is
connected for conversation mode.
To initiate an outbound call, the TIP/RING loop is closed by the loop relay. After the telco equip-
ment has detected loop current, dial tone is transmitted from telco, until dialed digits are received
from the subscriber equipment (Model 640 trunk card). After dialing is complete, the line is
placed into conversation mode while the destination telco equipment processes dialout, etc.
The call is terminated from the telco CO or PABX by opening the TIP/RING loop. The Model
640 opens the loop relay to break the TIP/RING current and disconnect the end-to-end line.
Ground Start Trunk Configuration
The PABX ground start trunk configuration is illustrated in Section 11 (Part No. 024-0079). This
circuit is an inbound-only configuration; that is, the Model 640 cannot originate ground start
calls to PABX equipment. This is not a problem since paging is one-way communication. For the
PABX ground start trunk, -48 V
DC
battery is provided from the Model 640 DAPT (as opposed to
being provided by the TELCO CO for subscriber ground start service).
When idle, the TIP is floating (not connected) and the RING is biased to -48 V
DC
through the
ground start detection opto-isolator (lower 4N26 shown in 024-0079). The PABX or telco equip-
ment must short the RING to ground briefly to initiate inbound dialing to the Model 640. Once
the ground pulse has been detected, the loop relay closes, isolating the ground start detector and
connecting battery to the TIP/RING loop. A brief period of time lapses wherein the PABX
continues to hold the RING to ground until loop current is detected by the PABX. During this
interval the -48 V
DC
ballast lamp glows brighter than normal (appears as a brighter flash). Once
the PABX has detected loop current, the ground start is removed and the TIP/RING loop is
closed. Digits are dialed into the Model 640 and conversation mode is initiated.
The call is terminated by either the PABX or the Model 640 opening the TIP/RING loop.
E&M Trunk Configurations
There are two E&M configurations available for the Model 640 chassis. The Dual Trunk Inter-
face card (Part No. 702-9361) can be configured for E&M trunks using the matrix plug or an
optional Dual Trunk 4-Wire Audio Interface (Part No. 702-9488) can be installed in the second
trunk card slot.
The configurations are compared in Table 4. The major difference between the two setups is the
number of signaling leads used for the audio portion of the channel. The TO TEL and FROM
TEL audio paths are completely isolated between the two directional signal pairs in the 4-wire
configuration.