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6.2.
THE LINE INTERFACE SECTION (SEE BLOCK DIAGRAM Fig. 17)
6.2.1.
INTRODUCTION
This section consists of the telephone line interface, bell detector, charge-pulse detector, CLIP detector hook switch, pulse
dialing circuits, audio circuits, DC mask & line impedance circuits, power supplies, and battery charger circuits.
dialing circuits, audio circuits, DC mask & line impedance circuits, power supplies, and battery charger circuits.
6.2.2.
TAX DETECT (SEE Fig. 19)
The tax detection will detect the 16kHz burst which is picked up on the CHARGE_PULSE line. The LC filter (L3 and C5) block
the signal so that it does not interfere with speech signals in the line circuit. D5 provides overvoltage protection for the
CHARGE_PULSE input port of the BBIC. The RC filter components provide high pass filtering which attenuates the speech
(below 4kHz) while allowing the charge pulse burst (16kHz) to pass.
the signal so that it does not interfere with speech signals in the line circuit. D5 provides overvoltage protection for the
CHARGE_PULSE input port of the BBIC. The RC filter components provide high pass filtering which attenuates the speech
(below 4kHz) while allowing the charge pulse burst (16kHz) to pass.
6.2.3.
TELEPHONE LINE INTERFACE (SEE Fig. 19)
The telephone line is connected to a bridge rectifier D8. Surge suppressor SA3 protects against excessive line voltages. Test
points are TP40 (A), TP26 (B). A 16 kHz notch filter L3 and L5 block the 16 kHz “charge pulse” signal from the rest of the line
input circuitry. Bridge rectifier D8 provides for lines of either polarity. The output of D8 is “Line +” (TP50) and “Line -” which is
ground.
points are TP40 (A), TP26 (B). A 16 kHz notch filter L3 and L5 block the 16 kHz “charge pulse” signal from the rest of the line
input circuitry. Bridge rectifier D8 provides for lines of either polarity. The output of D8 is “Line +” (TP50) and “Line -” which is
ground.
6.2.4.
EARTH RECALL SERVICE OPTION (SEE Fig. 19)
The circuit can be configured for connection to signalling earth by a service engineer as an optional feature.
In order to facilitate this the components listed below are to be fitted by a Service Engineer/Technician.
This modification connects the ’E’ and ’b’ contacts of the plug when the relay is switched on.
The relay is controlled by the ’EARTH’ signal from the BBIC, IC6 pin 68. It can be programmed to operate in Earth or Flash
mode. The factory preset is Flash mode.
mode. The factory preset is Flash mode.
* If you want to change the time of EARTH RECALL, please change the value of EEPROM (ADR, 0F0E, 0F0F, 0F10).
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KX-TCD725GM
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