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7.2. The Line Interface Section (See BLOCK DIAGRAM Fig. 17)
7.2.1. Introduction
This section consists of the telephone line interface, earth recall, BBIC Interface, hook switch, audio circuits, line impedance
circuits , power supplies, and battery charger circuits.
circuits , power supplies, and battery charger circuits.
7.2.2. 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). Bridge rectifier D8 provides for lines of either polarity. The output of D8 is Line + (TP39) and
Line - which is ground.
points are TP40 (A), TP26 (B). Bridge rectifier D8 provides for lines of either polarity. The output of D8 is Line + (TP39) and
Line - which is ground.
7.2.3. BBIC Interface (See Fig. 19)
Potential divider circuit containing components C12, C14, R9, R37, R20, R38, R19 and R21. This circuit provides an interface
between the telephone Line and the BBIC. It detects the signals for the Bell, Clip, SMS and Meterpulse functions. The DSP in
the BBIC then deciphers the signals, and then in conjuction with the software in the Flash ROM the funtions are implemented.
between the telephone Line and the BBIC. It detects the signals for the Bell, Clip, SMS and Meterpulse functions. The DSP in
the BBIC then deciphers the signals, and then in conjuction with the software in the Flash ROM the funtions are implemented.
Fig. 19
7.2.4. Hookswitch (See Fig. 20)
T8 is the hookswitch, driven by T9. When the phone is off-hook, the HOOK control signal from the BBIC will be a high logic level
(+3V), and both transistors will be on, thus T8 will loop the line. The zenner diode D10 protects transistors T11 to T13 against
transient line voltages.
(+3V), and both transistors will be on, thus T8 will loop the line. The zenner diode D10 protects transistors T11 to T13 against
transient line voltages.
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KX-TCD775RUS
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