Auto Disconnect Circuit; Parallel Connection Detect Circuit - Panasonic KX-TG2257BXS Service Manual

15.7. 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 DSP (DCIN) 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.
Note: DSP is IC201.
See CPU DATA (Base Unit) (P.65)
You can enable or disable the Auto Disconnect function.
See Check Record (P.32).

15.8. 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 off hook by detecting changes in the T/R voltage.
It is like an "Auto Disconnect Circuit".
Circuit Operation:
Parallel connection detection when on hook:
When on hook Q7 is ON, the voltage is monitored DSP (DCIN). There is no parallel connection if the voltage is 2.50 V or higher,
while a parallel connection is deemed to exist if the voltage is lower.
Parallel connection detection when off hook:
When off hook Q7 is OFF, the voltage is monitored DSP (DCIN); the presence/absence of a parallel connection is determined when
the voltage changes by 0.2 V or more.
57
KX-TG2257BXS