Panasonic KX-TC1709LBB, Руководство по обслуживанию

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13.5. Telephone Line Interface
Telephone Line Interface Circuit:
Function
· Bell signal detection
· ON/OFF hook and pulse dial circuit
· Side tone circuit
· Auto-disconnect circuit/Parallel connection detection circuit
Bell signal detection and OFF HOOK circuit:
In the idle mode, Q121 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
→
L101
→
R103
→
C103
→
Q101
→
DSP pin 27. [BELL]
When the CPU (DSP) detects a ring signal, Q121 turns on, thus providing an off-hook condition (active DC current flow through
the circuit) and the following signal flow is for the voice signal.
T
→
D101
→
Q121
→
R140/R139
→
C139
→
R138
→
R136
→
D131
→
D101
→
L102
→
P101
→
R
ON HOOK Circuit:
Q121 is open, Q121 is connected as to cut the DC loop current and to cut the voice signal. The unit is consequently in an on-
hook condition.
Pulse Dial Circuit:
DSP (2) turns Q121 ON/OFF to make the pulse dialing.
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 Q131 is canceled by the chancellor circuit of DSP.
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KX-TC1709LBB