Telephone Line Interface - Panasonic KX-TCD530SLM Service Manual

20.3. Telephone Line Interface

<Function>
- Bell signal detection
- Clip signal detection
- ON/OFF hook circuit
- Audio circuits
Bell & Clip (: Calling Line Identification Presentation: Caller ID) signal detection:
In the standby mode, Q4 is open to cut the DC loop current and decrease the ring load.
When ring voltage appears at the TP21 (A) and TP19 (B) leads (when the telephone rings), the
signal is transferred as follows;
- A C13 R17
- B C12 R16
ON/OFF hook circuit:
R24 IC2 Pin 107 (CID IN +)
R32 IC2 Pin 112 (CID IN -)
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