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Voice terminals work like special input/output (I/O)
devices. The control unit performs all the decision making
for the system while voice terminals act as the system’s
sensors. Voice terminals inform the control unit of button
depressions and feature status. They also inform the user
of specific conditions by flashing lights or generating
tones.
Voice terminals are connected to the control unit by a
4-pair wire. Each pair has a specific function:
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Voice 1 pair. The control unit uses this pair of wires
for the primary audio path to and from the voice
terminal. The control unit selects this pair to complete
the path for outgoing, incoming, and intercom calls.
Control pair. The control unit receives information
on voice terminal status and user input on this pair of
wires. It also uses this path to send ringing and lighting
instructions to the voice terminal.
Power pair. This pair provides power to the voice
terminal.
Voice 2 pair. The control unit uses this pair of wires
for the secondary audio path to and from the voice
terminals. This pair is used with the analog voice
terminal to provide the Voice Announcement to Busy
Voice Terminal and the Simultaneous Voice and Data
features.
Voice terminals used with the MERLIN II system are
listed here. Refer to Figure 1-6 for examples of analog
voice terminals, including the MERLIN II Display
Console. Figure 1-7 shows digital voice terminals.
1-26 System Hardware