Panasonic KX-TG2220BXB, Service Manual, Page: 51 / 86

16.7. 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 (DCIN1) 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.59)
You can enable or disable the Auto Disconnect function.
16.8. 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 the set is on hook, the voltage is monitored at DSP (DCIN0). 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 the set is off hook, the voltage is monitored at DSP (DCIN1); the presence/absence of a parallel connection is determined
when the voltage changes by 0.2 V or more.
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KX-TG2220BXB / KX-TG2220B XF / KX-TG2220B XS / KX-TGA226BXB / KX-TGA226BXF / KX-TGA226BXS