Panasonic KX-T2371MXW, Service Manual

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12. CIRCUIT OPERATIONS
Note: The circuit diagram may be modified at any time with the development of new technology.
12.1. Telephone Line Interface and Pulse Dial Circuit
When the hook switch SW1 is ON (off-hook), the circuit is closed, and current is supplied to the
base of Q2 via the diode bridge D1 and Q2 is On Q1 is ON (OFF-HOOK condition).
Q1 and Q2 are the dial pulse generating circuits, and are driven by the DIALER (IC1), when the
DIALER Pin 10 of IC1 is LOW Q2 is OFF and Q1 is OFF. (break) If port Pin 10 is HIGH Q2 is
ON Q1 is ON. (make)
12.2. Tone Dial Circuit
Function:
The tone dialing circuit consists of a DTMF (Dual Tone Multi Frequency) signal generator
(outputted from Pin 11 of the IC1) for tone dialing, and also a circuit for outputting the signal to
line.
The DTMF circuit identifies inputs from the 12 keys (1,2,3,4,5,6,7,8,9,0, and #) by means of a
total of seven frequencies, that is four low frequencies (Low group) and three high frequencies
(High group).
Circuit Description:
When a dial key is pressed, a DTMF signal is output from Pin 11 of IC1 as an analog synthetic
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