Panasonic KX-TG6700BXB Service Manual page 19

4.5.6. 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 mes-
sage receiving, OGM transmitting and Hold status.
Circuit Operation:
Operational amplifier with high value resisters is used in order to isolate both lines.
This circuit gain is controlled by the signal (inverse RLY). When the base unit is in off-hook condition, the control signal logic is
zero.
This circuit transforms the voltage of the line and DSP monitors the result of the transformation.
When the DSP detects the voltage drop 0.2 V or more by parallel-connected telephone off-hook, the unit will disconnect the line.
Pin 113 is for Line 1.
Pin 128 is for Line 2.
Line 1
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KX-TG6700BXB/KX-TGA670BXB