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 R24 IC2 Pin 107 (CID IN +)
- B C12 R16 R32 IC2 Pin 112 (CID IN -)
ON/OFF hook circuit:
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