Parallel Connection Detect Circuit/Auto Disconnect Circuit - Panasonic PRL Series Service Manual

4.5.8.

Parallel Connection Detect Circuit/Auto Disconnect 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.
Circuit Operation:
Parallel connection detection when on hook:
When on hook, the voltage is monitored at pin 32 of IC501. There is no parallel connection if the voltage is
0.54 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, the voltage is monitored at pin 17 of IC501; the presence/absence of a parallel connection is determined by
detecting the voltage changes.
If the Auto disconnect function is ON and statuses are Hold, receiving ICM, OGM transmitting, BBIC disconnects the line after
detecting parallel connection is off hook.
R160
+
R178 C173
RX
Pin25 of IC501
TX
Pin27 of IC501
HOOK
Pin19 of IC501
PARADET
Pin17 of IC501
ADC1
Pin33 of IC501
ADC0
Pin32 of IC501
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Q161
C
B
E
R164 R151
C184
17
KX-PRL260/KX-PRL262/KX-PRD260/KX-PRD262/KX-PRLA20
Q141
R141
C101
Q142
C
B
D101
E
+
3 2
_
4
1
C102
R115
R116
L1T
L1R
P101