Telephone Line Interface - Panasonic KX-PRL260B Service Manual

KX-PRL260/KX-PRL262/KX-PRD260/KX-PRD262/KX-PRLA20
4.5.7.

Telephone Line Interface

Telephone Line Interface Circuit:
Function
• Bell signal detection
• ON/OFF hook and pulse dial circuit
• Side tone circuit
Bell (RINGING) signal detection and OFF HOOK circuit:
In the idle mode, Q141 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:
L1T  C105  R103  R110  R111 R112  BBIC pin18(RINGING)
When the CPU (BBIC) detects a ring signal, Q141 turns on, thus providing an off-hook condition (active DC current flow through
the circuit). Following signal flow is the DC current flow.
T  D101  Q141  Q161  R163  D101  P101  R
ON HOOK Circuit:
Q141 is open, Q141 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:
Pin 19 of BBIC turns Q141 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 Q161 is
canceled by the canceller circuit of BBIC.
R178
RX
Pin25 of IC501
TX
Pin27 of IC501
HOOK
Pin19 of IC501
PARADET
Pin17 of IC501
ADC1
Pin33 of IC501
ADC0
Pin32 of IC501
RINGING
Pin18 of IC501
CIDOUT
Pin24 of IC501
CIDINn
Pin23 of IC501
CIDINp
Pin21 of IC501
LSRn
Pin28 of IC501
R160
+
Q161
C
B
E
C173
R164 R151
C184
R111
C111 C113
R112
BELL signal detection
C109
R109
Q141
R141
Q142
C
B
E
R115
R116
R101 C103
R103
C105
R102 C104
C106
R104
16
C101
OFF Hook
D101
L1T
+
3
2
_
4
1
L1R
C102
P101