Panasonic KX-TG2650N, Руководство по обслуживанию

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12.9. Parallel Connection Detection 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 Q115 is ON, the
voltage is monitored pin 40 of IC501. There is no parallel connection if the voltage is 1.65 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 Q115 is OFF, the voltage is
monitored pin 40 of IC501; the presence/absence of a parallel connection is determined when the
voltage changes by 0.2 V or more.
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