Matsushita Electric KX-TC1461LAB, Руководство по обслуживанию

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12.5. Telephone Line Interface
Function:
- Bell signal detection
- ON/OFF hook and pulse dial circuit
- Side tone circuit
Bell signal detection and OFF HOOK circuit:
In the idle mode, Q3 is open to cut the DC loop current and decrease the ring load. When ring
voltage appears at the Tip (T)
and Ring (R) leads (When the telephone rings), the AC ring voltage is transferred as follows:
T L9 C7 R44 IC2-A, B CPU (Ring DET). [BELL]
When the CPU(IC3) detects a ring signal and press the TALK Key onto the handset. Q3 turns on,
thus providing an off-hook
condition (active DC current flow through the circuit) and the following signal flow is for the
loop current.
T L9 R52 T4 RLY1 L10 F1 R [OFF HOOK]
ON HOOK Circuit:
Q3 is open, Q3 connected as to cut the DC loop current via RLY1 and to cut the voice signal.
The unit is consequently in an on-hook
condition.
Pulse Dial Circuit:
DSP (Relay) turns Q3 ON/OFF to make the pulse dialing via RLY1.
Side Tone Circuit:
Basically this circuit prevents the TX signal from feeding back to RX signal.
As for this unit, TX signal feed back from IC2 is canceled by AC3 and so on.
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