Panasonic KX-TA1232 Service Manual page 37

(c) Pulse Dial Transmission Circuit
(d) 2 W~4 W Lines Conversion Circuit
(e) A/D, D/A Conversion Circuit
Call Interface Circuit consists eight lines corresponding to each call line.
(Transfer circuit at power failure are four lines.)
Circuit Operation:
(a) Bell Signal Detection Circuit
When CO line is idle, EXRLY pin of IC 111 is low, photocoupler PC101, PC102 are OFF. BELL pin
of IC111 is high. When there is an incoming signal at the CO line, the call signal is rectified by
zener diode D102 and D103 and photocoupler PC101, current flows to the photocoupler PC101
and PC101 turns ON. This causes BELL pins of IC111 to change form a high to low. This change
is detected as incoming call thus processing are executed.
Call Signal Path:
Tip-L102-L104-PC101(1-2)-R101-C102-L103-L101-SA103(4-2)-Ring
(b) DC Loop Formation Circuit
In the off-hook mode, EXRLY of IC111 is low.
DC Loop Path:
Tip-L102-L104-R118-D101(-+)-PC102(4-3)-Q101
D101(-)-F100-L103-L101-SA103(4-2)-Ring
(c) Pulse Dial Transmission Circuit
When off-hook, pulse dial transmission is executed by alternating on-hook and off-hook.
On-hook and off-hook is controlled by PC102. During the make position, dial pin of IC111 is low
level and PC102 is ON. During the break position, dial pin of IC111 is high level and PC102 is OFF.
At this time, BELL pin of IC111 become a low. Afterwards, BELL pin of IC111 monitors for a
change (low to high) for mote than 400ms. If more than 400 ms has been detected it assumes that
an on-hook state has occurred and the CO line circuit is restored to the idle state. The voice
signal is transmitted into the system via transformer T101.
(d) 2W-4W Lines Conversion Circuit
This circuit converts 2-line analog signals from CO line to 4-line signals. The voice analog signal
form the line is outputted from T101 to the 2-4 Line Conversion Circuit, and the circuit flow is
T101(4-6)-R116-5pin of IC102
IC102 is a CODEC. The voice analog signal is converted to PCM signal by this CODEC. PCM
signal from TSW is converted to voice analog signal by the CODEC. And the circuit flow is as
following.
2pin of IC102-IC108/R112-2 pin of IC101-R107-T101
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