Panasonic KX-FT21RS Serivce Manual page 128

KX-FT21RS
6.6.2. MODEM CIRCUIT OPERATION
The ASIC (IC1) has all the hardware satisfying the ITU-T standards mentioned previously.
The modem is included in IC1. The signal communicates with the TEL line through the analog front end IC (IC5) of digital/analog,
analog/digital convertor. The modem in IC1 is operated using the 20.736 MHz (x2) clock.
1. Facsimile Transmission/DTMF Line Send
The digital image data on the data bus is modulated in the modem (IC1), and sent to analog front end (IC5) as the digital data,
then it is converted to the analog signal there. Passing through IC9 and IC6, the signal is sent to NCU section.
[IC1 IC5 IC5(3)
(7) CN10 (1)]
[ ]: Digital section
2. Facsimile Reception
The analog image data which is received from the telephone line passes through the NCU section and enters pin 15 of the
analog front end (IC5). The signals that enter pin 15 of the analog front end (IC5) convert the analog signals to the digital
signals, then the data is sent to the modem (IC1).
TEL LINE D1
(11) IC103 (10)
[ ]: Digital section
3. DTMF Transmission
The DTMF signal generated in the ASIC (IC1) is sent to the analog front end (IC5) to perform the digital/analog conversion, then
output from pin 3 of IC5, and is then sent to the circuit on the same route as used for facsimile transmission.
(DTMF Monitor Tone)
[IC1 IC5 IC5(3)
(62) IC1 (63) C62
[ ]: Digital section
4. Call Tone Transmission
This is the call signal which is generated in the ASIC (IC1) and sent to the speaker.
[IC1 (59) R28
C67 CN10 (9)]
[ ]: Digital section
5. Busy/Dial Tone Detection
The path is the same as FAX receiving.
C48 R37 R38 IC9 (2)
CN202 (1) C106 R103
Q4 (E) Q4 (C) C8 T101
CN102 (10) [CN9 (10)
C48 R37 R38
IC8 (5) IC8 (7) C67
C45 R35 IC8 (2) IC8 (1)
CN202 (9) R122 IC102 (4)
IC9 (1) C53 IC6 (2)
R102 T101 C8
R104 C107 R112
IC6 (10) IC6 (11) R33
IC9 (2) IC9 (1) C54
CN10 (9)] CN202 (9)
C27 R13 IC1 (62)
IC102 (5) SPEAKER
128
IC6 (1) C58 R49
Q4 (C) Q4 (E) D1 TEL LINE
IC101 (6) IC101 (7)
C43 IC5 (15) IC5
R44 IC8 (2) IC8 (1)
R122 IC102 (4) IC102 (5)
IC1 (63) C62
IC9 (6) IC9
C127 IC103
IC1]
C27 R13 IC1
SPEAKER
IC8 (5) IC8 (7)