Panasonic KX-TC1743B, Service Manual

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13.7. Auto Disconnect Circuit
Function:
This circuit is used to detect the fact that another telephone connected to the same line is OFF-
HOOK while the unit is in a receiving status or OGM transmitting status.
Circuit Operation:
The voltage DCIN of DSP is monitored. If a parallel-connected telephone is put into an OFF HOOK
status, the presence/absence of a parallel connection is determined when the voltage changes
by 0.2V or more.
When the set detects the parallel-connected telephone is OFF HOOK status, the line is
disconnected.
13.8. Parallel Connection Detect Circuit
Function:
In order to disable call waiting and stutter tone functions when using telephones connected in
parallel, it is necessary to have a circuit that judges whether a telephone connected in parallel is
in use or not. This circuit determines whether the telephone connected in parallel is on hook or
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